Dr. Jeff Masters' WunderBlog

Grading the forecasts for Irene; Katia organizing; threat of a Gulf of Mexico storm

By: JeffMasters, 04:38 PM GMT die 31o August, anno 2011

Recovery from the destruction left behind by Hurricane Irene continues in the mid-Atlantic and New England states today. Irene's storm surge, winds, and record rains likely did $3 - $6 billion in insured damage to the U.S., according to AIR-Worldwide. Since actual damages are typically double insured losses, Irene's total price tag will likely be $6 - $12 billion, making it one of the top 20 most expensive hurricanes to hit the U.S. Irene will be one of the most expensive Category 1 hurricanes ever; the record is held by 1972's Hurricane Agnes, which did $11.8 billion in damage (2010 dollars.) As AIR Worldwide notes in their press release, part of this damage is due to the costs of evacuation for the 2 million people that were evacuated. It costs approximately $1 million to evacuate each mile of U.S. coast warned (Aberson et al., 2006). This number will be higher for more densely populated areas of the coast, such as Miami, and may be a factor of six lower for the North Carolina coast (Whitehead, 2003). So were we over-warned during Irene? Could the costs of the storm been lower due to better forecasts and fewer evacuations?


Figure 1. The National Hurricane Center forecast for Hurricane Irene issued five days before it hit Long Island, NY, compared with the actual track of Irene. The landfall locations along the coasts of North Carolina, New Jersey, and New York were pretty much spot-on, though the time of arrival was off by a few hours. The NOAA Environmental Visualization Laboratory has a nice satellite animation of the storm's track superimposed on the NHC's cone of uncertainty forecast.

Well, the official NHC track forecast for Irene was remarkably good; the 5-day forecast was pretty much spot-on for landfall locations, though the timing of when the storm would arrive at the coast was off by a few hours (Figure 1.) This remarkably accurate forecast undoubtedly reduced the costs of unnecessary preparations, and probably saved many lives. NHC track forecasts have improved by over 50% since 1990. The average error in a 24-hour forecast was about 105 miles in 1990, and has averaged near 50 miles the past few years. NHC director Bill Read stated in a interview this week that had Hurricane Irene come along before the recent improvements in track forecasting, hurricane warnings would have been issued for the entire Florida, Georgia, and South Carolina coasts. At an average cost of $1 million per mile of coast over-warned, this would have cost over $700 million. We can credit the investments made in hurricane research, improved satellites, and better computer models for the majority of this improvement. When we consider that government funding for hurricane research has averaged $20 million per year during much of the past two decades, the roughly $200 million spent on hurricane research over the past 20 years was paid back by over a factor of three during just one storm. According to a 2007 presentation at the 61st Interdepartmental Hurricane Conference, the improved hurricane forecasts between 2000 - 2006 resulted in savings of $3 billion compared to what the forecasts of the 1990s would have cost.

What about intensity forecasting?
Progress in making better intensity forecasts of hurricanes, though, has lagged. Over the past twenty years, there has been virtually no improvement in forecasting how strong or weak a hurricane will grow. NHC predicted Irene would hit North Carolina as a Category 3 storm, but it hit at Category 1 strength. Had the intensity forecast been better, many evacuations that were done for Irene could have been avoided. The failure of the intensity forecast led to many accusations that the storm was over-hyped, and an unnecessary amount of expensive preparations and evacuations were done. While I did see some over-hype by the media, I did not think it was more excessive than what has been the case for previous hurricanes. Nate Silver of the New York Times makes some interesting comparisons of the media attention given to Irene versus previous storms, and finds that Irene had about the same amount of media attention as hurricanes Ike and Gustav of 2008. Given in inexperience of the mid-Atlantic and New England coasts with hurricanes, our lack of skill in making intensity forecasts, and the potential for high storm surge damage due to the size of Irene and its landfall during the highest tides of the month, I thought that the overly-cautious approach to evacuations along the coast was warranted.

Better intensity forecasts threatened by budget cuts
Better intensity forecasts of hurricane are possible, but it will take a large investment in hurricane research over an extended time to do that. Such an effort is underway; we are currently in year three of a ten-year program called the Hurricane Forecast Improvement Project (HFIP), funded at just over $1 million per year. The goals of the HFIP are to reduce the average errors of hurricane track and intensity forecasts by 20% within five years and 50% in ten years with a forecast period out to 7 days. In an interview I did last fall with the leader of the project, Dr. Frank Marks of NOAA's Hurricane Research Division, he expressed to me optimism that the program could meet its objectives, provided it remains fully funded. Some of the experimental computer models developed by HFIP have done very well so far during the 2011 hurricane season, so I see reason for optimism, too. However, this project is in serious danger of failure, due to the current budget-cutting emphasis in Washington D.C. A key tool we need to make better intensity forecasts is to have detailed measurements inside the core of the hurricane from instrumented aircraft. Without detailed observations, there is no hope of making a good intensity forecast, no matter how good your model is. During Hurricane Irene, the two P-3 hurricane hunter aircraft and G-IV jet operated by NOAA's Aircraft Operations Center flew continuously into the storm, taking detailed measurements via dropsonde and Doppler radar that were fed in real time to the experimental HFIP computer models. In theory, these measurements by the Hurricane Hunters should be able to significantly improve our intensity forecasts over the coming years. However, the current proposed budget from the House of Representatives mandates a $400 million cut for NOAA, and the NOAA Hurricane Hunters are slated to have their budget cut by 40%, from $29 million to $17 million per year. If these cuts materialize, the ability of the NOAA Hurricane Hunters to continue to aid improvements in hurricane forecasting will be seriously impacted. Many of the critical technologies used operationally now by the Air Force Hurricane Hunters and NOAA jet to improve hurricane forecasts--dropsondes, real-time high-density observations, and the SFMR surface wind measuring instrument--were developed on the NOAA P-3s as research projects, then were migrated to operational use once they proved their worth. The cost of hurricane damages in the U.S. has been doubling every ten years since the 1960s, and is expected to continue to double every ten years, even without the likely coming increase in storm surge damages due to accelerating sea level rise. A Category 1 hurricane doing $10 billion in damage should be a wake-up call that we need to continue our investments in hurricane research to reduce the costs of the inevitable coming storms. Slashing funding by 40% for a research group that was instrumental in saving $700 million in costs from just one storm makes no sense, and I hope Congress will reconsider the proposed cuts for NOAA's Aircraft Operations Center.

References
Whitehead, J.C., 2003: "One million dollars per mile? The opportunity costs of Hurricane evacuation", Ocean and Coastal Management 46, 1069.

Tropical Storm Katia
Tropical Storm Katia continues its long trek across the Atlantic Ocean today, and is expected to arrive at a position several hundred miles north of the Northern Lesser Antilles Islands by Monday. At this time, it appears unlikely that the islands will receive tropical storm-force winds from Katia. Satellite images show that Katia is a well-organized storm with plenty of heavy thunderstorms. The storm has good upper-level outflow channels to the north and south, is under light wind shear, and is traversing warm waters, so it should be able to overcome any dry air problems by Thursday and intensify into a hurricane. It is looking less likely that Katia will affect land. Dr. Bob Hart's Historical Tropical Cyclone Probability web page suggests shows that tropical storms in Katia's current position have an 11% chance of hitting North Carolina, a 12% chance of hitting Canada, a 5% chance of hitting Florida, and a 62% chance of never hitting land. It will be two more days before our computer models will be able to assess the threat to land, though, as Katia is currently still very far out at sea.


Figure 2. The morning run of the GFS Ensemble prediction. The ensemble prediction was done by taking a lower-resolution version of the GFS model and changing the initial distributions of temperature, pressure, and humidity randomly by a few percent to generate an ensemble of 20 different computer projections of where Katia might go. The operational (highest-resolution) version of the GFS model (white line) is usually more accurate, but the ensemble runs give one an idea of the uncertainty in the forecast. Very few of the ensemble members are currently showing a threat to the U.S. Canada is more at risk than the U.S., according to this model.

Gulf of Mexico disturbance a threat to develop
Surface winds over the Gulf of Mexico are rising today in advance of the approach of a tropical wave currently over the Western Caribbean, western tip of Cuba, and Mexico's Yucatan Peninsula. This wave is headed west-northwest at 10 - 15 mph, and is under a high 20 - 30 knots of wind shear. The wave is slowly beginning to build an increased amount of heavy thunderstorms, and this process will accelerate on Thursday when the wave enters the Gulf of Mexico. By Friday, when the wave will be near the Louisiana or Texas coast, wind shear is expected to drop to low to moderate levels, and the wave may be able to organize into a tropical depression. This process will likely take several days, and formation of a tropical depression is more likely Saturday or Sunday. NHC is giving the wave just a 10% chance of developing into a tropical depression by Friday morning. Regardless, this system will spread heavy rains to portions of the Gulf Coast by Friday, with the Upper Texas coast and the coast of Louisiana the most likely recipients of heavy rain. Strong onshore winds raising tides to 1 - 2 feet above normal are likely over Louisiana beginning on Friday, and coastal flood statements have been issued for the region. Three of our four top models for predicting tropical cyclone development forecast that a tropical depression will form this weekend or early next week, and I think it is at least 50% likely we will have Tropical Depression 13 on our hands by Monday. However, steering currents will be weak in the Gulf, and it is difficult to predict where the storm might go.The GFS model has a possible tropical depression forming by Sunday off the coast of Mississippi, then moving east-northeast over the Florida Panhandle on Monday. The ECMWF model forms the storm on Monday off the coast of Texas, and leaves the storm stalled out there through Wednesday. The UKMET model forms the storm Saturday off the coast of Louisiana, and leaves it stalled out there through Monday. If the storm did remain in the Gulf of Mexico for three days as some of the recent model runs have been predicting, it would be a threat to intensify into a hurricane.

Related posts:
Big money for hurricane research? My October 27, 2006 post.

Jason Samenow at the Washington Post has an excellent post, Hurricane Irene hype: over the top media coverage or justified?

Andrew Freedman at the Washington Post talked earlier this month how lack of funding to replace an aging weather satellite may degrade weather forecasts beginning in 2016. Michael Conathan at climateprogress.org had a more detailed analysis of the issue in a February blog post.

Andy Revkin at the New York Times discussed in his Dot Earth blog yesterday how cuts in the USGS stream gauge network will hamper flood forecasting.

Jeff Masters

Hurricane

Updated: 12:15 PM GMT die 01o September, anno 2011

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Irene's rains heaviest on record in Vermont; Tropical Storm Katia forms

By: JeffMasters, 03:40 PM GMT die 30o August, anno 2011

Record flooding continues in the Northeast from Irene's torrential rains. Hardest hit was Vermont, where heavy rains in the weeks prior to Irene's arrival had left soils in the top 20% for moisture, historically. Irene dumped 5 - 8 inches of rain over large sections of Vermont, with a peak of 11.23" at Mendo. The reading from Mendo was the greatest single-day rainfall in Vermont's history, according to wunderground's weather historian Christopher C. Burt, beating the 9.92" that fell at Mt. Mansfield on 9/17/1999 during the passage of Tropical Storm Floyd. The 13.30" that fell on East Durham, NY during Irene was just shy of New York State's all-time 1-day rainfall record: 13.70" at Brewster on 9/16/1999, from Tropical Storm Floyd.


Figure 1. Wunderphotographer 43BJAGER recorded this image of a house in Sharon, Vermont, that started out the week on the other side of this underpass.

According to the final Hurricane Irene summary from the NWS, the storm dropped 20" of rain in two locations, one in North Carolina and one in Virginia. Here are the highest rain amounts from the hurricane for each state:

Virginia Beach, VA: 20.40"
Jacksonville, NC: 20.00"
East Durham, NY: 13.30"
Freehold Twp, NJ: 11.27"
Mendon, VT: 11.23"
Ellendale, DE: 10.43"
New Hartford, CT 10.15"
Baxter St. Park, ME: 9.91"
Savoy, MA: 9.10"
Lafayette, PA: 8.82"
Pinkham North, NH: 7.33"
Warren, RI: 5.37"

Tropical Storm Katia forms
Tropical Storm Katia formed this morning in the far Eastern Atlantic off the coast of Africa. Katia will be in a moist, low wind shear environment with ocean temperature 1 - 2°C above the threshold needed to support a hurricane, and should be able to intensify to major hurricane strength when it passes to the north of the Lesser Antilles Islands 5 - 6 days from now. It is possible that some of the outer spiral bands of the storm might bring heavy rain squalls to the northern Lesser Antilles, but it would be a surprise if the core of the storm passed through the islands. The long term fate of Katia is unknown. Dr. Bob Hart's Historical Tropical Cyclone Probability web page suggests shows that tropical storms in Katia's current position have a 19% chance of hitting North Carolina, a 16% chance of hitting Canada, an 11% chance of hitting Florida, and a 47% chance of never hitting land.


Figure 2. The morning run of the GFS Ensemble prediction. The ensemble prediction was done by taking a lower-resolution version of the GFS model and changing the initial distributions of temperature, pressure, and humidity randomly by a few percent to generate an ensemble of 20 different computer projections of where Katia might go. The operational (highest-resolution) version of the GFS model (white line) is usually more accurate, but the ensemble runs give one an idea of the uncertainty in the forecast.

Katia is the 11th named storm this year, and comes a full twelve days before the half-way point of the Atlantic hurricane season. Climatologically, September 10 marks the half-way point. A typical hurricane season has just 10 - 11 named storms, so we've already had a whole season's worth of storms before reaching the half-way point. At this rate, 2011 will see 25 named storms, making it the 2nd busiest season on record, behind 2005. Katia's formation date of August 30 puts 2011 in 5th place for earliest date of arrival of the season's 11th storm. Only 2005, 1995, 1936, and 1933 had an earlier 11th storm.

Gulf of Mexico development possible late this week
Several of our best computer models for predicting formation of tropical cyclones, the GFS and ECMWF, are predicting that an upper level pressure interacting with a tropical wave now over the the Western Caribbean could combine to spawn a tropical depression in the Gulf of Mexico late this week or early next week. The formation location is likely to be off the coast of Louisiana or Texas, but the track of the system is hard to predict at this point.


Figure 3. Portlight volunteer Thomas Hudson clears a driveway yesterday in Hollywood, Maryland.

Portlight disaster relief effort in Maryland
Hurricane Irene heavily damaged the town of Hollywood, Maryland, when a tornado cut off electric power, water, and phone service. Portlight and Team Rubicon volunteers arrived before emergency personnel, after following up on a local tip. What they found was an isolated area whose plight was unknown to the larger community. Most residents were trapped at their homes by heavy debris. Portlight and Team Rubicon worked for two days to clear paths to each address, extract vehicles from debris, and cut down trees that constituted safety hazards. Portlight also instructed local residents how to operate and maintain chainsaws and safely clear debris. No other volunteer organizations or emergency personnel arrived at any time, and Portlight succeeded in meeting the specific needs of the underserved, unserved, and forgotten. Visit the Portlight blog to learn more; donations are always welcome.

I'll have a new post on Wednesday discussing if the evacuations and media hype surrounding Irene were excessive.

Jeff Masters

Hurricane

Updated: 01:25 PM GMT die 31o August, anno 2011

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Irene's 1-in-100 year rains trigger deadly flooding

By: JeffMasters, 04:00 PM GMT die 29o August, anno 2011

Hurricane Irene is gone, but the huge hurricane's torrential rains have unleashed one of the Northeast's greatest flood disasters. Videos of rampaging rivers in Vermont, New York State, New Jersey, and surrounding states attest to the extreme nature of the great deluge Hurricane Irene brought. Numerous rivers and creeks throughout the Northeast crested above their highest flood stages on record over the past 24 hours. The previous records were mostly set during some of the great hurricanes of 50 - 60 years ago--Hazel of 1954, Connie and Diane of 1955, and Donna of 1960. Vermont, where 3 - 7 inches of rain fell in just twelve hours, was particularly hard-hit. Otter Creek in Rutland, Vermont crested at 17.21 feet, 3.81' above its previous record, and more than 9 feet above flood stage. In northern New Jersey and Southeast New York, where soils were already saturated from the region's wettest August on record even before Irene arrived, record flooding was the norm. According to imagery from metstat.com, Irene's rains were a 1-in-100 year event for portions of eight states.


Figure 1. Water levels on Vermont's Otter Creek in Rutland, Vermont crested at 17.21 feet, 3.81' above its previous record, and more than 9 feet above flood stage. Image credit: USGS.

Here are a few of the rivers in the Northeast that set all-time flood height records over the past 24 hours, which I found using our wundermap with the USGS rivers layers turned on:

Mettawee River, Middle Granville, NY
Hoosic River, North Bennington, VT
Saxton River, Saxtons RIver, VT
Schoharie Creek, Gilboa, NY
Esopus Creek, Coldbrook, NY
Passaic River, Millington, NJ
Rockaway River, Boonton, NJ
Pompton River, Pompton Plains, NJ
Millstone RIver, Blackwells Mills, NJ
Assunpink Creek, Trenton, NJ

And here are the unofficial maximum 24-hour rainfall amounts each state received from Irene, as compiled by our weather historian, Christopher C. Burt:

North Carolina: 14.00" Bunyan
Virginia: 12.52" Ft. Eustis
Maryland: 12.96" Plum Point
Delaware: 8.50" Federalsburg
Pennsylvania: 8.00" Goldsboro
New Jersey: 10.20" Wayne
New York: 11.48" Tuxedo Park
Connecticut: 8.70" Burlington
Massachusetts: 9.10" Savoy
Vermont: 7.60" Walden
New Hampshire: 6.09" 5SE Sandwich
Rhode Island: 5.37" Warren
Maine: 6.11" Phillips

Newark, NJ broke its all-time 24-hour precip record with a total of 8.92" (8/27-28)--old record 7.84" on 8/27-28/1971. Also, New York City, Philadelphia, and Newark now have August 2011 as their rainiest month in recorded history. Overall damages from Irene could range from $5 billion to $10 billion, according to Kinetic Analysis, a risk assessment firm that specializes in natural disaster impact. This would put Irene between 13th and 24th place on the list of the most damaging hurricanes ever to hit the U.S. Irene is very likely to have its name retired. The multi-billion dollar price tag from Irene puts the year 2011 in first place for the greatest number of billion-dollar disasters in one year, ten. The previous record was nine such disasters, set in 2008.

Irene cuts though barrier island, isolates North Carolina's Outer Banks
Irene's large surge surge and pounding waves breached North Carolina's Pea Island in two places Sunday, cutting U.S. Highway 12 and isolating the Outer Banks from the rest of the world. According to Dr. Rob Young of Western Carolina University, Irene did little damage to the ocean-front homes along North Carolina's Outer Banks, but there was significant soundside flooding impacting many areas of Duck, Kitty Hawk, Collington Village, and Roanoke Island. The $30-plus million dollar beach nourishment project at Nags Head survived the storm, although there has been some loss of sand along the beach.


Figure 2. Hurricane Irene's storm surge and winds carved two new channels through Pea Island on North Carolina's Outer Banks. This cut, near the town of Rodanthe, is the smaller of the two cuts. Highway 12 connecting the Outer Banks to the mainland will need to be re-built across these two cuts. Image credit: Western Carolina University.

Tropical Depression 12
Tropical Depression Twelve formed this morning from a strong tropical wave that had moved off the coast of Africa. TD 12 is undergoing some moderate wind shear of 10 - 20 knots due to strong easterly winds, which is keeping most of the storm's heavy thunderstorm activity limited to the west aide. This shear should relax as TD 12 pulls away from Africa, and allow the storm to become Tropical Storm Katia. Ironically, today is the 6-year anniversary Hurricane Katrina's landfall on the Gulf Coast, and Katia is the name that was selected to replace Katrina after that name was retired. Forecast tracks from the long-range GFS and ECMWF models suggest that Bermuda and Canada might be the only land area threatened by TD 12, but it is too early to be confident of this.


Figure 3. Tropical Depression Twelve at 8:10 am EDT August 29, 2011, as seen by the MODIS instrument on NASA's Terra satellite. Image credit: NASA.

A break in Texas' drought coming
One other area we need to watch later this week is the Gulf of Mexico. A significant shift in the atmospheric circulation is predicted for the region, with the ridge of high pressure that has brought Texas its record heat and drought predicted to shift eastwards and allow a flow of moist, tropical air into the state. A low pressure region is forecast to develop in the Gulf near the coast of Texas on Wednesday or Thursday, and this low will need to be watched for tropical development. The shift in the large scale weather pattern does not signal a permanent end to the Texas drought, but it should bring welcome rains and cooler temperatures to the Lone Star state beginning on Thursday. This will be a relief to the residents of Austin, where the temperature topped out at 112°F yesterday--the hottest day in Austin's recorded history, tied with September 5, 2000. By Labor Day, hot and dry weather will settle back in over the state, but the new ridge of high pressure will be weaker, and temperatures will not be as hot as this week's.

Jeff Masters

Updated: 02:23 PM GMT die 30o August, anno 2011

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Irene hits New Jersey and New York; Jose threating Bermuda; 92L forms

By: JeffMasters, 04:45 PM GMT die 28o August, anno 2011

Hurricane Irene hit New Jersey ten miles north of Atlantic City at 5:30 am EDT, as a minimum-strength Category 1 hurricane with 75 mph winds. Irene is only the second hurricane since 1851 to hit New Jersey. At 9 am EDT, Irene made a third U.S. landfall over Long Island, NY, and New York City, as a tropical storm with 65 mph winds. Top wind gusts measured in New York City were 60 mph at Central Park at 3:58 am; 67 mph at La Guardia at 4:10 am; and 59 mph at JFK Airport at 1:33 am. A 91 mph gust was recorded in Sayville, NY on the Central Long Island coast, at 7:02 am. Emergency managers reported that the nearby town of Lindenhurst (population 28,000), on the south side of Long Island, was mostly under water due to a storm surge. The storm surge at The Battery on the southern shore of Manhattan reached 4.0 feet, overtopping the sea wall in several locations. Fresh water run-off from Irene's torrential rains, riding on top of a 3 to 4-foot storm surge, allowed the swollen East and Hudson Rivers to overflow at the edges of Manhattan. Irene's rains have now ended in New York City, after accumulating to 7.60" at Central Park. This brings total rainfall for the month of August in New York City to 19.68", making it the wettest month in the city since record keeping began in 1869. The previous record was 16.85", set in September 1882. Philadelphia, PA and Newark, NJ have also set all-time wettest month records, thanks to Irene's rains. The 19.40" of rain that has fallen in Philadelphia this August is probably the most rain any major city in the Northeast, U.S. has received since 22.43" fell in Newark, NJ in August 1843, according to wunderground's weather historian, Christopher C. Burt.


Figure 1. Storm surge at The Battery on the south end of New York City's Manhattan Island as of noon EDT Sunday, August 28, 2011. The green line is the storm surge, which is the difference between the observed water level (red line) and what the water level should have been without the hurricane (blue line). At 4:45 am, the storm surge peaked at 4.0 feet. The surge declined to about 3 feet during the high tide cycle, then rose again to near 3.9 feet as the tide started going out. Image credit: NOAA Tides and Currents.


Figure 2. Total rainfall over the past 30 days along the mid-Atlantic coast and New England has topped 15 inches (purple colors) in many areas, making August the wettest month in recorded history for the cities of Philadelphia, Newark, and New York City. Image credit: NOAA/AHPS.

Irene's rains bringing significant river flooding
Irene brought more than eight inches of rain to a long stretch of the Atlantic coast from North Carolina to New York. NOAA's Significant River Flood Outlook is showing that significant river flooding is already occurring along coastal regions of North Carolina, Virginia, Maryland, Delaware, and New Jersey, and is expected to spread to Eastern Pennsylvania, eastern New York, Western Massachusetts, and most of Vermont and New Hampshire.

The 1903 Vagabond Hurricane
The only other hurricane to hit New Jersey since 1851 was the 1903 Category 1 Vagabond Hurricane. According to Wikipedia, the Vagabond Hurricane caused heavy damage along the New Jersey coast ($180 million in 2006 dollars.) The hurricane killed 57 people, and endangered the life of President Theodore Roosevelt, who was sailing on a yacht near Long Island, NY, when the hurricane hit. New Jersey only rarely gets hit by hurricanes because it lies in an portion of the coast that doesn't stick out much and is too far north.


Figure 3. The path of the 1903 Vagabond Hurricane, the only other hurricane to hit New Jersey since 1851.

Tropical Storm Jose forms
Tropical Storm Jose formed this morning in surprise fashion, managing to maintain enough heavy thunderstorms in the face of very high wind shear of 40 - 55 knots to become the season's tenth named storm. Jose does not have long to live, due to the strong upper-level winds from Hurricane Irene that are creating the shear. Jose will likely bring strong winds near tropical storm force later today when it passes just west of Bermuda. Satellite loops show that there is very little heavy thunderstorm activity associated with Jose, and Bermuda will see much less rain than is usual for a tropical storm passing so close.

Elsewhere in the tropics: Invest 92L forms
A strong tropical wave located off the coast of Africa, about 200 miles south of the Cape Verde Islands, is moving west at 10 mph, and has been designated Invest 92L by NHC this morning. This system has a large amount of heavy thunderstorm activity and moderate amount of spin, and appears likely to develop into a tropical storm later this week, as all of the computer models are developing it. NHC is giving 92L a 40% chance of developing into a tropical depression by Tuesday. This storm will be moving more slowly across the Atlantic than Irene did, and will take at least 6 days to reach the Lesser Antilles Islands. Forecast tracks from the long-range GFS and ECMWF models suggest that Bermuda might be the only land area threatened by 92L, but it is too early to be confident of this.

Hottest day in Houston's history
The mercury hit 109°F (42.8°C) yesterday at Houston's George Bush Intercontinental Airport, tying September 4, 2000 as the hottest day in the city's history. Yesterday was the also the hottest August day on record in Houston, besting the 108°F reading of August 18, 1909. This year, Houston has set its record for all-time hottest temperature, most 100° days in a year (36, old record was 32, and 4 is normal), and most consecutive 100° days (24, old record was 14.) Weather records in Houston go back to 1889. Houston needs 20.18" of rain to get to normal levels of rainfall for the year. Today's high is predicted to be 107°F in Houston, so yesterday's record may be in danger of being broken today. By the end of the week, Houston is expected to cool down below 100°, and a weather pattern conducive for bringing summer rains will move in.

I'll have a new post Monday morning.

Jeff Masters

Hurricane

Updated: 02:30 PM GMT die 31o October, anno 2012

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Irene sends 4.5 foot storm surge up Chesapeake Bay

By: JeffMasters, 12:45 AM GMT die 28o August, anno 2011

The eye of Hurricane Irene is back over water, after the hurricane completed a 11-hour crossing of eastern North Carolina. Irene came ashore over Cape Lookout, North Carolina at 7:30 am EDT this morning as a Category 1 hurricane with 85 mph winds. The Cedar Island Ferry Terminal measured sustained winds of 90 mph, gusting to 115 mph at 7:19am, as measured by a Department of Transportation official. I suspect this measurement came when a thunderstorm near Irene's center collapsed, sending a powerful downburst to the surface. A trained spotter on Atlantic Beach, NC measured sustained winds of 85 mph, gusting to 101 mph at 10:35 am. The Hurricane Hunters measured 80 mph winds over water at the time of landfall. However, no regular weather station or buoy has measured sustained hurricane force winds in Irene, with the highest winds being 67 mph at the Cape Lookout, North Carolina buoy as Irene made landfall. Winds have peaked along the coast of Virginia, where sustained winds of 61 mph were observed at 6 pm EDT at Chesapeake Bay Light. Irene's passage over land weakened the storm slightly, and satellite loops show more dry air has wrapped into the storm. The radar presentation of Irene visible on the Norfolk, VA radar is still very impressive--Irene is dropping torrential rains over a huge area--but there is much less rain over the storm's southeastern quadrant, over water. Radar-estimated rainfall shows a 50 mile-wide band of 8+ inches of rain has fallen from where Irene made landfall at Cape Lookout, North Carolina, northwards to Dover, Delaware. Some isolated amounts of 15+ inches may have fallen, according to the radar estimates. Bunyan, NC has received 14.00" so far, and the towns of Washington, New Bern, Grifton, Newport-Croatan, Wonona, NC, all received more than ten inches. Norfolk, Virginia had received 7.73" as of 7pm EDT, and Suffolk, Virginia, 8.00".


Figure 1. True-color MODIS image of Hurricane Irene over North Carolina taken at 11:35 am EDT August 27, 2011. At the time, Irene was a Category 1 hurricane with 85 mph. Image credit: NASA.

Storm surge damage from Irene
The storm surge and wave action from Irene is likely to cause the storm's greatest damage. High tide is near 7 - 8 pm EDT tonight, meaning that the storm surges occurring now will be some of Irene's most damaging. The highest surges measured at any of NOAA's regular tide gauges at 8 pm were 4.5 feet at Sewells Point in Norfolk Virginia and Oregon Inlet, NC. Higher surges are occurring father inland where narrow inlets funnel the storm surge to higher elevations. It remains unclear if the ocean will overtop Manhattan's sea wall at The Battery Sunday morning during the 8 am high tide. Latest storm surge forecasts from SUNY Stony Brook predict a peak water level of 2.4 meters above Mean Lower Low Water (MLLW) at 7:15 am Sunday, which would put the ocean right at the top of the sea wall. Presumably, waves from the hurricane's winds would then push some water over the top of the wall, but it is uncertain whether or not this would cause significant flooding. The storm surge was already 1 foot at 8 pm tonight. Storm surge flooding continues to be a major concern all along the coast of Long Island Sound; I recommend the SUNY Stony Brook storm surge page for those interested in looking at observed and predicted storm surge levels along coast New Jersey, New York, and Connecticut.


Figure 2. Storm surge at Sewell's Point in Norfolk, Virginia as of 8 pm EDT Saturday August 27, 2011. The green line is the storm surge, which is the difference between the observed water level (red line) and what the water level should have been without the hurricane (blue line). At 8 pm, the storm surge was 4.5 feet. Image credit: NOAA Tides and Currents.


Figure 3. Distribution of Irene's wind field at 6:30 pm EDT Saturday August 27, 2011, as observed by the Hurricane Hunters, land stations, and buoys. The right front quadrant of the hurricane had all of the storm's shrinking hurricane-force winds (yellow and orange colors.) Tropical storm-force winds (heavy black like bounding the light blue area) extended out 290 miles from the center of Irene over water, but very few areas of land were receiving tropical storm force winds. Image credit: NOAA/AOML/HRD.

Wind damage
The emergence of Irene's eye over water will slow the storm's rate of weakening, but the storm is under too much wind shear to allow it to intensify. The latest wind distribution map from NOAA's Hurricane Research Division (Figure 3) shows that all of Irene's hurricane-force winds are on the storm's east side, and also the large majority of the tropical storm-force winds. When Irene makes its 2nd landfall on Long Island, NY on Sunday, coastal locations to the right of the eye will likely experience top sustained winds of 50 - 60 mph. Coastal areas of Maryland, Delaware, New Jersey, and the New York CIty area will mostly see top winds in the 40 - 55 mph range, since they will be on the weaker left side of the storm. Winds on the upper floors of skyscrapers will be up to 30% higher, but I expect there will be only isolated problems with New York City skyscrapers suffering blown out windows. The winds from Irene in New York City will be no worse than those experienced during some of the city's major Nor'easter winter storms of the past twenty years.

Tornadoes
Four tornadoes have been spawned by Irene, two in coastal North Carolina last night, and two in coastal Virginia today. At least two homes have been destroyed, and ten others damaged by the tornadoes. NOAA's Storm Prediction Center has issued a tornado watch for all of coastal Delaware, New Jersey, New York, and Connecticut.

Links
Our Weather Historian, Christopher C. Burt, has an excellent post on Historic Hurricanes from New Jersey to New England.

For those of you wanting to know your odds of receiving hurricane force or tropical storm force winds, I recommend the NHC wind probability product.

Wunderground has detailed storm surge maps for the U.S. coast.

The National Hurricane Center's Interactive Storm Surge RIsk Map, which allows one to pick a particular Category hurricane and zoom in, is a good source of storm surge risk information.

Jeff Masters

Hurricane

Updated: 12:48 AM GMT die 28o August, anno 2011

Permalink

Irene hits North Carolina

By: JeffMasters, 04:37 PM GMT die 27o August, anno 2011

Hurricane Irene roared ashore over Cape Lookout, North Carolina at 7:30 am this morning. The Cedar Island Ferry Terminal measured sustained winds of 90 mph, gusting to 110 mph at 7:19am, and a trained spotter on Atlantic Beach measured sustained winds of 85 mph, gusting to 101 mph at 10:35 am. The Hurricane Hunters measured 80 mph winds over water at the time of landfall. Winds at the Cape Lookout, North Carolina buoy, which the eye passed directly over, peaked at 67 mph as Irene made landfall. At 10am EDT, top winds observed at Cape Hatteras on the Outer Banks of North Carolina were 53 mph, gusting to 73 mph. Winds are rising now along the coast of Virginia, with sustained winds of 56 mph, gusting to 62 mph observed at 10 am EDT at Chesapeake Bay Light. Satellite loops show a large but deteriorating storm with dry air intruding to the southwest. The radar presentation of Irene visible on the Norfolk, VA radar is very impressive--Irene is dropping torrential rains over a huge area.


Figure 1. Radar-estimated precipitation from Irene as of 12:18 pm EDT August 27, 2011. An expanding region of rains in excess of ten inches (pick colors) was observed north of where the center made landfall.

Storm surge damage from Irene
The storm surge and wave action from Irene is likely to cause the greatest damage, and this will be a historic coastal flooding event for many regions of the mid-Atlantic and Northeast. A storm surge of 8.5 feet was reported this morning in North Harlow, NC, and three feet in New Bern, NC. Significant wave heights (the average height of the largest 1/3 of the waves) reached 27 feet at Onslow Bay, NC this morning, and wave heights along the New Jersey shore Sunday morning during the time of high tide are expected to be 15 - 20 feet, according to the NOAA Wavewatch III model (Figure 2.) A storm surge of 3 - 6 feet is expected near Atlantic City, NJ Sunday morning, during the time of high tide. With 15 - 20 foot waves expected on top of this storm surge, there will be tremendous damage to the coast and low-lying structures. Storm surge is also a major concern for New York City. The latest NWS forecast is calling for a 5 - 8 foot storm surge in New York Harbor, which would easily top the flood walls protecting the south end of Manhattan if the storm surge occurs at high tide. High tide is near 8 am Sunday morning. A research storm surge model run by SUNY Stonybrook predicts that water levels at The Battery at the south end of Manhattan will peak at 2.2 meters above Mean Lower Low Water (MLLW) at high tide Sunday morning, which would be about six inches below the top of the flood wall (which is 5 feet above mean sea level.) Waves on top of the surge would likely spill over the top of the floodwall in this scenario, and cause some flooding in southern Manhattan. Andy Revkin's Dot Earth blog has links to a storm surge animation for New York City done by the SUNY Stonybrook group. Climate Central has a nice satellite image showing which parts of New York Harbor are below five feet in elevation. Storm surge heights of up to eight feet are predicted in Western Long Island Sound, and 3 - 6 feet along much of the New England coast from New York to Massachusetts. This is going to be a damaging coastal flooding event for this stretch of coast, though perhaps not as damaging as the one New Jersey will experience.


Figure 2. Predicted wave heights along the U.S. coast from NOAA's Wavewatch III model for 8am EDT Sunday, August 28, 2011. This is the time of high tide, and this model is suggesting that the coast of New Jersey will be subject to battering waves 15 - 20 feet high at the time of high tide.

Inland flooding damage from Irene
Inland flash flooding and river flooding from torrential rains are a major concern. Latest radar-estimated rainfall amounts in North Carolina already exceed ten inches in some locations. Cedar Island, NC has reported 7.21" as of 11am EDT, and a 100 mile-wide swath of 8+ inches of rain will likely fall from Eastern North Carolina northwards along the coast, through New York City, and into Vermont and New Hampshire during the next two days. Destructive river flooding will be a significant danger from New Jersey northwards to Southeast New York, where soils are saturated and run-off will be the greatest.


Figure 3. Distribution of Irene's wind field at 9:30 am EDT Saturday August 27, 2011, as observed by the Hurricane Hunters, land stations, and buoys. The right front quadrant of the hurricane had all of the storm's hurricane-force winds (yellow and warmer colors, bounded by the heavy black line between the "50" and "60" knot thin black lines.) Tropical storm-force winds (heavy black like bounding the light blue area) extended out 260 miles from the center of Irene. Irene's storm surge damage potential has dropped to 4.3 on a scale of 0 to 6, down from a high of 5.1 yesterday. Image credit: NOAA/AOML/HRD.

Wind damage
Irene is slowly deteriorating, but the storm is too large to weaken quickly. The latest wind distribution map from NOAA's Hurricane Research Division (Figure 3) shows that all of Irene's hurricane-force winds are on the storm's east side, so only North Carolina's Outer Banks will get winds of 75 - 80 mph. The coast from Virginia northwards through New Jersey will see tropical storm-force winds of 50 - 70 mph from Irene. These strong winds, when combined with the torrential rains that are falling, will cause widespread tree damage and power failures that will affect millions of people. When Irene makes its 2nd landfall on Long Island, NY on Sunday, coastal locations to the right of the eye will likely experience top sustained winds of 60 -70 mph.

Lady Liberty not in danger from Irene
The Statue of Liberty is not vulnerable to a storm surge, since the good lady stands atop a 65-foot high foundation and 89-foot high granite pedestal. However, the 305' height of the lady's torch above the foundation means the statue will experience winds a full Saffir-Simpson category higher than winds at the surface. The statue is rated to survive a wind load of 58 psf, which is roughly equivalent to 120 mph winds (Category 3 hurricane). However, a mid-strength Category 2 hurricane with 105 mph winds will be able to generate 120 mph winds at a height of 300 feet, and would theoretically be capable of toppling the Statue of Liberty. Winds from Irene should stay below 80 mph at 300 feet, and not pose a threat to the Statue of Liberty.

Tornadoes
Two tornadoes were reported in coastal North Carolina last night. One tornado destroyed 2 homes and damaged 6 others in Columbia, with several minor injuries, and the other hit Belhaven, damaging multiple trailers. NOAA's Storm Prediction Center is calling for a slight risk of severe weather along coast Virginia, Maryland, and Delaware today. We might see five or ten tornadoes from Irene over the next two days, but the atmosphere is not unstable enough for Irene to generate as many tornadoes as we're used to seeing from a landfalling hurricane. A tornado watch is posted for coastal areas from Eastern North Carolina northwards to Southern New Jersey.

Insurance company AIR-Worldwide is estimating that insured damages from Irene in the U.S. will be $1.5 - $6 billion. They estimate losses in the Caribbean at $0.5 - $1.1 billion from Irene, 60% in the Bahamas.

Typhoon Nanmadol
Over in the Western Pacific, Typhoon Nanmadol has weakened to a Category 3 storm after battering the Philippines as a Category 4 super typhoon with 155 mph winds. At least two people have been killed in the heavy flooding there. Nanmadol is a threat to Taiwan, and Wunderground meteorologist Elaine Yang (who hails from Taiwan), has the details in her blog.

Links
Our Weather Historian, Christopher C. Burt, has an excellent post on Historic Hurricanes from New Jersey to New England.

Joe Romm at climateprogress.org has a thoughtful piece called, How Does Global Warming Make Hurricanes Like Irene More Destructive?

For those of you wanting to know your odds of receiving hurricane force or tropical storm force winds, I recommend the NHC wind probability product.

Wunderground has detailed storm surge maps for the U.S. coast.

The National Hurricane Center's Interactive Storm Surge RIsk Map, which allows one to pick a particular Category hurricane and zoom in, is a good source of storm surge risk information.

Jeff Masters

Hurricane

Updated: 07:22 PM GMT die 27o August, anno 2011

Permalink

Hurricane Irene Weakens on its Approach to North Carolina

By: JeffMasters, 07:58 AM GMT die 27o August, anno 2011

As of 300AM EDT, Hurricane Irene was located at 33.7N, 76.5W, 60 miles south of Cape Lookout. It was moving north-northeast at 14 mph with maximum sustained winds of 90 mph, making it a Category 1 storm on the Saffir-Simpson scale. Irene has a minimum central pressure of 952 mb.

Hurricane warnings are in effect for the US Atlantic coast from the Little River inlet in North Carolina to Sagamore Beach, Massachusetts. Tornado watches are also in effect for the North Carolina/Virginia/Maryland coast. Figure 1 shows the hurricane, tropical storm, and tornado watches and warnings for Irene. Remember, a hurricane warning means hurricane conditions are expected, and tropical storm force winds (greater than 34 mph) will occur within 36 hours. Tropical storm warning means that tropical storm force winds are expected in the next 36 hours, but hurricane conditions are not. A tropical storm watch means tropical storm force winds are possible within 48 hours.

To find out if you need to evacuate, please contact your local emergency management office. They will have the latest information. People living in New York City can find their evacuation zone here or use this map. FEMA has information on preparing for hurricanes. FEMA also has a blog describing their response to Irene.


Figure 1 Map of watches and warnings taken at 225AM EDT, August 27, 2011

Satellite Views
Figure 2 shows that Irene is a large storm, with outflow reaching from South Carolina to Long Island, NY. Irene's eye is not visible.


Figure 2 IR satellite view of Irene taken at 226AM EDT, August 27, 2011

Track Forecast

Irene is forecast to make landfall on the North Carolina coast Saturday morning as a category 1 storm with sustained winds around 90 mph. I believe that Irene's center of circulation will make landfall somewhere between Cape Lookout and Okracoke on the Outer Banks around 9-10 am. Irene should then move roughly north, along the mid-Atlantic coastline before making landfall in western Long Island. However, it is important to not focus solely on the track forecast. Irene is a large storm with a large windfield and equally large areas of storms and showers. It's impact will be felt over a wide swath of the northeastern US.


Figure 3 Official track forecast of Irene at 11PM EDT, Aug. 26.

Irene and Flooding
Six to ten inches of rain are possible along Irene's track from North Carolina north into New England, with 15 inches possible in isolated areas. Radar estimates indicate at least 5 inches have already fallen near Morehead City, NC. As a result, flooding is very likely. The Hydrometeorological Prediction Center (HPC) has issued their Significant River Flood Outlook for the next five days shown in figure 4. HPC thinks that river flooding from the Delmarva peninsula to northwestern Maine is likely, while river flooding in much of the rest of the northeastern US is possible.


Figure 4 Significant River Flood Outlook issued by HPC.

Impacts

Tropical storm forces winds are occuring at Cape Lookout now, with hurricane force winds expected on the North Carolina coast later today. Use this Wundermap to keep track of how the winds are behaving around the North Carolina coastline. Within the hurricane warning area in North Carolina, storm surge is expected to be 6-11 feet above ground. This is our storm surge forecast map. To see how high the tides are running, NOAA has an excellent page collecting all of the relevant tide gauges.

People living on the the east coast of the US from the Carolinas to Cape Cod should continue monitoring Irene and be in the process of finishing their hurricane preparations. If you have not started preparing for this storm, start immediately. If an evacuation order is given, please follow it, unless it is unsafe to do so. Irene will be a large storm, impacting areas far from the storm center track.

Links

If you're curious about power outages, here are some maps: Dominion Power Outage Map (NC/VA), Progress Energy Outage Map (NC/SC), and NOVEC Outage Map (Northern Virginia).

Dr. Masters will have a new blog entry this morning, and there will be another blog this afternoon. I'll be back with another blog entry late tonight.

Stay safe,

Dr. Rob Carver

Hurricane

Permalink

Irene continues to weaken

By: JeffMasters, 08:46 PM GMT die 26o August, anno 2011

Satellite data and measurements from the Hurricane Hunters show that Irene continues to weaken. A 1:32 pm EDT center fix by an Air Force Reserve aircraft found that Irene's eyewall is still gone, and the central pressure had risen to 951 mb from a low of 942 mb this morning. The winds measured in Irene near the surface support classifying it as a strong Category 1 hurricane or weak Category 2. Satellite imagery shows a distinctly lopsided appearance to Irene's cloud pattern, with not much heavy thunderstorm activity on the southwest side. This is due to moderate southwesterly wind shear of 10 - 20 knots. This shear is disrupting Irene's circulation and has cut off upper-level outflow along the south side of the hurricane. No eye is visible in satellite loops, but the storm's size is certainly impressive. Long range radar out of Wilmington, North Carolina, shows that the outermost spiral bands from Irene have moved ashore over North Carolina. Winds at buoy 41004 100 miles offshore from Charleston, SC increased to 47 mph, gusting to 60 mph at 3 pm EDT, with significant wave heights of 25 feet.


Figure 1. MODIS satellite image of Hurricane Irene taken at 11:50 am EDT Friday August 26, when Irene was a Category 2 hurricane with 105 mph winds. The eyewall collapsed several hours before this image was taken, and no eye is apparent. Image credit: a href=http://rapidfire.sci.gsfc.nasa.gov/gallery/ NASA.


Figure 2. Distribution of Irene's wind field at 3:30 pm EDT Friday August 26, 2011, as observed by the Hurricane Hunters and buoys. The right front quadrant of the hurricane had about 90% of the storm's hurricane-force winds (yellow and warmer colors, bounded by the heavy black line between the "50" and "60" knot thin black lines.) Tropical storm-force winds (heavy black like bounding the light blue area) extended out 290 miles from the center of Irene. Image credit: NOAA/AOML/HRD.

Forecast for Irene
With its eyewall collapsed and just 18 more hours over water before landfall, Irene does not have time to build a new eyewall and intensify. The storm is too large to weaken quickly, and the best forecast is that Irene will be a strong Category 1 hurricane at landfall in North Carolina on Saturday. Based on the latest wind analysis from NOAA's Hurricane Research Division (Figure 2) and Irene's continued weakening trend, I predict that the 80-mile section of North Carolina coast to the right of where Irene makes landfall will receive sustained hurricane-force winds of 75 - 85 mph on Saturday at landfall; the 80-mile section of coast to the left will receive 55 - 75 mph winds. High wind shear of 30 knots will begin ripping into Irene Sunday morning when it is near Southern New Jersey, and more rapid weakening will occur. By the time Irene arrives on Long Island Sunday afternoon, it will probably have top sustained winds in the 65 - 75 mph range. However, since Irene is such a huge storm--tropical storm force winds extend out up to 290 miles from the center--it has set a massive amount of the ocean's surface in motion, which will cause a much larger storm surge than the winds would suggest. At 3:30 pm EDT this afternoon, a wind analysis from NOAA/HRD (Figure 2) indicated that the potential storm surge damage from Irene still rated a 5.0 on a scale of 0 to 6. This is equivalent to the storm surge a typical Category 4 hurricane would have. While this damage potential should steadily decline as Irene moves northwards and weakens, we can still expect a storm surge one full Saffir-Simpson Category higher than Irene's winds when it impacts the coast. Since tides are at their highest levels of the month this weekend due to the new moon, storm surge flooding will be at a maximum during the high tidal cycles that will occur at 8 pm Saturday night and 8 am Sunday morning. Wherever Irene happens to be at those times, the storm surge damage potential will be maximized. I continue to give a 20% chance that a 3 - 4 foot storm surge high enough to over-top the Manhattan flood walls and swamp the New York City subway system will occur on Sunday. The latest 11 am probabilistic storm surge map from NHC shows a 20 - 30% chance of a storm surge in excess of 3 feet in New York Harbor (Figure 4.) Keep in mind that these maps are calculated for normal tide level, and this weekend's high tides will be nearly 1 foot above normal.

Insurance company AIR-Worldwide is estimating that insured damages from Irene in the U.S. will be $1.5 - $6 billion. They estimate losses in the Caribbean at $0.5 - $1.1 billion from Irene.


Figure 3. Storm surge heights, in feet above normal tide level, which have a 20 percent chance of being exceeded during the next 3 days.  The graphic is based upon an ensemble of Sea, Lake, and Overland Surge from Hurricanes (SLOSH) model runs using the current National Hurricane Center (NHC) official hurricane advisory. The exceedance heights depend on the historical accuracy of NHCs forecasts of hurricane track, and wind speed, and an estimate of storm size. Image credit: NOAA.


Figure 4. Overall chance that storm surges will be greater than 3 feet above normal tide levels during the next 3 days.  The graphic is based upon an ensemble of Sea, Lake, and Overland Surge from Hurricanes (SLOSH) model runs using the current National Hurricane Center (NHC) official hurricane advisory.  Storm surge probabilities depend on the historical accuracy of NHCs forecasts of hurricane track, and wind speed, and an estimate of storm size. Image credit: NOAA.

Links
For those of you wanting to know your odds of receiving hurricane force or tropical storm force winds, I recommend the NHC wind probability product.

Wunderground has detailed storm surge maps for the U.S. coast.

The National Hurricane Center's Interactive Storm Surge RIsk Map, which allows one to pick a particular Category hurricane and zoom in, is a good source of storm surge risk information.

Wunderblogger Mike Theiss is in Nassau, documenting the storm's impact on the Bahamas.

Internet radio show on Irene at 4:30pm EDT
Wunderground meteorologists will be discussing Hurricane Irene on a special edition of our Internet radio show, the Daily Downpour, today (Friday) at 4:30pm EDT. Shaun Tanner , Tim Roche, Angela Fritz, and Rob Carver will take your questions. The email address to ask questions is broadcast@wunderground.com.

Jeff Masters

Hurricane

Permalink

Irene's eyewall collapses; further intensification unlikely

By: JeffMasters, 03:14 PM GMT die 26o August, anno 2011

Satellite data and measurements from the Hurricane Hunters show that Irene is weakening. A 9:21 am EDT center fix by an Air Force Reserve aircraft found that Irene's eyewall had collapsed, and the central pressure had risen to 946 mb from a low of 942 mb this morning. The highest winds measured at their flight level of 10,000 feet were 125 mph, which would normally support classifying Irene as a Category 3 hurricane with 115 mph winds. However, these winds were not mixing down to the surface in the way we typically see with hurricanes, and the strongest surface winds seen by the aircraft with their SFMR instrument were just 90 mph in the storm's northeast eyewall. Assuming the aircraft missed sampling the strongest winds of the hurricane, it's a good guess that Irene is a mid-strength Category 2 hurricane with 100 mph winds. Satellite imagery shows a distinctly lopsided appearance to Irene's cloud pattern, with not much heavy thunderstorm activity on the southwest side. This is due to moderate wind shear of 10 - 20 knots due to upper-level winds out of the southwest. This shear is disrupting Irene's circulation and has cut off upper-level outflow along the south side of the hurricane. No eye is visible in satellite loops, but the storm's size is certainly impressive. Long range radar out of Wlimington, North Carolina, shows that the outermost spiral bands from Irene are now beginning to come ashore along the South Carolina/North Carolina border. Winds at buoy 41004 100 miles offshore from Charleston, SC increased to 36 mph as of 10 am, with significant wave heights of 18 feet.


Figure 1. Distribution of Irene's wind field at 9:30 am EDT Friday August 26, 2011, as observed by the Hurricane Hunters and buoys. The right front quadrant of the hurricane had about 90% of the storm's hurricane-force winds (yellow and warmer colors, bounded by the heavy black line between the "50" and "60" knot thin black lines.) Tropical storm-force winds (heavy black like bounding the light blue area) extended out 290 miles from the center of Irene. Image credit: NOAA/AOML/HRD.

Forecast and storm surge potential for Irene
With its eyewall collapsed and just 24 more hours over water before landfall, it is unlikely Irene will have time to build a new eyewall and intensify. The storm is too large to weaken quickly, and the best forecast is that Irene will be a Category 2 hurricane at landfall in North Carolina on Saturday, and a rapidly weakening Category 1 hurricane at its second landfall in New England on Sunday. However, since Irene is such a huge storm--tropical storm force winds extend out up to 290 miles from the center--it has set a massive amount of the ocean's surface in motion, which will cause a much larger storm surge than the winds would suggest. At 9:30am EDT this morning, a wind analysis from NOAA/HRD (Figure 1) indicated that the potential storm surge damage from Irene rated a 5.1 on a scale of 0 to 6. This is equivalent to the storm surge a typical Category 4 hurricane would have. While this damage potential should gradually decline as Irene moves northwards and weakens, we can still expect a storm surge one full Saffir-Simpson Category higher than Irene's winds. Since tides are at their highest levels of the month this weekend due to the new moon, storm surge flooding will be at a maximum during the high tidal cycles that will occur at 8 pm Saturday night and 8 am Sunday morning. Wherever Irene happens to be at those times the storm surge damage potential will be maximized. A surge rivaling that experienced during Hurricane Isabel in 2003 is likely in northern NC, southern Maryland, and up Chesapeake Bay on Saturday night. Coastal New England from New York City to Massachusetts may also see storm surges characteristic of a Category 1 hurricane during Sunday morning's high tide, even if Irene has weakened to a tropical storm. I continue to give a 20% chance that a storm surge high enough to over-top the Manhattan flood walls and swamp the New York City subway system will occur on Sunday.

Wind damage
I don't think Irene is going to do a lot of wind damage to the mid-Atlantic states, since the eye of the storm will be just offshore, and the I-95 corridor from Virginia to New Jersey will be on the weak (left) side of the hurricane. The current wind distribution of Irene (Figure 1) shows almost all of the hurricane's winds are on the right side of the storm, and by the time the storm reaches Virginia, there will be likely be no hurricane-force winds on the left side of Irene. Sustained winds should stay below 74 mph (hurricane force), and wind damage will be similar to that wrought be some of the strongest Nor'easters of the past 20 years, from Virginia northwards to New York City. Since Irene will be steadily weakening as it approaches its second landfall on Long Island, I give a 50% chance that no mainland U.S. surface station in New England will record sustained hurricane-force winds. I do think it likely that one or more of the offshore islands--Block Island, Nantucket, and Marthas Vinyard--will get Category 1 hurricane winds. Though the wind damage to buildings will be similar to what the Northeast has seen during some of the more severe nor'easters of the past 20 years, tree damage will be much worse. The trees are in full leaf during hurricane season, and catch the wind much more readily than during the winter. Tree damage will very heavy, and we can expect trees in regions with saturated soils will fall over in high winds onto power lines. Irene is likely to cause one of the top-five most widespread power outages in American history from a storm. The record power outage from a Northeast storm was probably the ten million people that lost power during the great Blizzard of 1993. I don't think Irene's power outages will be quite that extensive, but several million people will likely lose power.

Irene likely to bring destructive fresh water flooding
In addition to storm surge, flash flooding and river flooding from Irene's torrential rains are the main threats. The hurricane is expected to bring rains in excess of 8" to a 100-mile-wide swath from Eastern North Carolina northwards along the coast, through New York City. The danger of fresh water flooding is greatest in northern New Jersey, Southeast Pennsylvania, and Southeast New York, where the soils are saturated from heavy August rains that were among the heaviest on record. New Jersey has had its 6th wettest August on record, with most of that rain falling in the past two weeks. Expect major river flooding throughout New Jersey the Delmarva Peninsula, and regions near New York City, as Irene's rains run off the saturated soils directly into the rivers. In general, the heaviest rains will fall along the west side of the hurricane's track, and the greatest wind damage will occur on the east side. I don't think flooding from heavy rains will be a huge concern in North Carolina, which is under moderate to severe drought. Irene's rains are likely to do some good in Southeast Virginia, where a fire triggered by lightning from a thunderstorm on August 4 sparked a fire in the Dismal Swamp that is burning out of control. Right now, it does not appear that tornadoes will be a major concern, but there will probably be a few weak tornadoes. Hurricane Bob of 1991, the last hurricane to affect New England, spawned six tornadoes, most of them weak F-0 and F-1 twisters.


Figure 2. Predicted rainfall for the 5-day period ending at 8 am EDT Wednesday August 31, as issued by NOAA/HPC.

Links
For those of you wanting to know your odds of receiving hurricane force or tropical storm force winds, I recommend the NHC wind probability product.

Wunderground has detailed storm surge maps for the U.S. coast.

The National Hurricane Center's Interactive Storm Surge RIsk Map, which allows one to pick a particular Category hurricane and zoom in, is a good source of storm surge risk information.

Wunderblogger Mike Theiss is in Nassau, documenting the storm's impact on the Bahamas.

Internet radio show on Irene at 4:30pm EDT
Wunderground meteorologists will be discussing Hurricane Irene on a special edition of our Internet radio show, the Daily Downpour, today (Friday) at 4:30pm EDT. Shaun Tanner , Tim Roche, Angela Fritz, and Rob Carver will there, and I will be available if my schedule permits. Listeners can email in or call in questions. The email address to ask questions is broadcast@wunderground.com.

Portlight mobilizes for Irene
The Bahamas have been hit hard by Irene, and unfortunately, it appears that the Northeast U.S. may have its share of hurricane victims before Irene finally dissipates. My favorite disaster relief charity, Portlight.org, is mobilizing to help, and has sent out their relief trailer and crew to North Carolina. Check out this blog to see what they're up to; donations are always needed.

Jeff Masters

Hurricane

Updated: 04:39 PM GMT die 26o August, anno 2011

Permalink

Category 3 Irene Approaches The Carolina Coastline

By: JeffMasters, 06:19 AM GMT die 26o August, anno 2011

As of 200AM EDT, Hurricane Irene was located at 28.7N, 77.3W, 460 miles south-southwest of Cape Hatteras. It was moving north at 14 mph with maximum sustained winds of 115 mph, making it a Category 3 storm on the Saffir-Simpson scale. Irene has a minimum central pressure of 942 mb. Outside of the US, hurricane warnings are still in effect for Grand Bahama and the Abaco islands. In the US, hurricane warnings are in effect for the coast of North Carolina from the Little River inlet north to the Virginia border. Hurricane watches are in effect from the NC/Virginia border north to Sandy Hook, New Jersey. Figure 1 shows the hurricane and tropical storm watches and warnings for Irene. Remember, a hurricane warning means hurricane conditions are expected, and tropical storm force winds will occur within 36 hours. A hurricane watch means that hurricane conditions are possible and tropical storm force winds are expected within 48 hours.

To find out if you need to evacuate, please contact your local emergency management office. They will have the latest information. FEMA has information on preparing for hurricanes. FEMA also has a blog describing their response to Irene.


Figure 1 Map of watches and warnings taken at 1215AM EDT, August 26, 2011

Satellite Views
Figure 2 shows that Irene is a large storm, with outflow reaching from Florida to North Carolina. Irene's eye is visible in the infrared imagery.


Figure 2 IR satellite view of Irene taken at 100AM EDT, August 26, 2011

Track Forecast

Irene is forecast to make landfall on the North Carolina coast Saturday afternoon. It will likely be a Category 3 storm, with windspeeds around 115 mph. As Irene moves northwards through the mid-Atlantic region it will weaken considerably. On Sunday, Irene's center will pass through the Tri-State region of New Jersey, New York, and Connecticut, with impacts spread over a wider region due to Irene's size.


Figure 3 Official track forecast of Irene at 11PM EDT, Aug. 25.

Irene and Flooding
Six to ten inches of rain are possible along Irene's track from the Carolinas northward, with 15 inches possible in isolated areas. As a result, flooding is very likely. The Hydrometeorological Prediction Center (HPC) has issued their Significant River Flood Outlook for the next five days shown in figure 4. HPC thinks that river flooding in eastern Pennsylvania and New Jersey is likely, while flooding along the rest of the northeastern US is possible.


Figure 4 Significant River Flood Outlook issued by HPC.

Impacts

Tropical storm forces winds will reach the southern North Carolina coast by late Friday, with hurricane force winds arriving Saturday. Within the hurricane warning area in North Carolina, storm surge is expected to be 5-10 feet above ground. This is our storm surge forecast map.

People living on the the east coast of the US from the Carolinas to Cape Cod should closely monitor Irene and be in the process of finishing their hurricane preparations. If you have not started preparing for this storm, start immediately. If an evacuation order is given, please follow it. Irene will be a large storm, impacting areas far from the storm center track.

Dr. Masters will have a new blog entry this morning, and there will be another blog this afternoon. There will be a special online broadcast at 430PM with Shaun Tanner, Tim Roche, Dr. Masters, Angela Fritz and me. Please email any questions you have to broadcast@wunderground.com. We will be taking phone calls at 415-983-2634. I'll be back with another blog entry late tonight.

Thanks for reading,

Dr. Rob Carver

Hurricane

Updated: 06:44 AM GMT die 26o August, anno 2011

Permalink

Irene slightly weaker, but still very dangerous

By: JeffMasters, 08:59 PM GMT die 25o August, anno 2011

An Air Force Reserve hurricane hunter aircraft investigating Irene has found a slightly weaker storm. As of 4pm EDT, the strongest surface winds seen by the aircraft with their SFMR instrument were 91 mph in the storm's northeast eyewall. Highest winds measured at their flight level of 10,000 feet were 114 mph. Assuming the aircraft missed sampling the strongest winds of the hurricane, it's a good guess that Irene has fallen to Category 2 strength with 100 - 105 mph winds, even though the official advisory is higher. The aircraft noted that the eyewall was missing a large chunk on it southwest side, but the central pressure was about the same as early this morning, 950 mb. Satellite imagery from late this morning and early this afternoon showed a distinctly lopsided appearance to Irene's cloud pattern, with not much heavy thunderstorm activity on the southwest side. This was due to moderate wind shear of 10 - 20 knots due to upper-level winds out of the southwest. This shear was able to disrupt Irene's circulation while it was attempting to complete an eyewall replacement cycle, resulting in dry air getting wrapped into the core, which can be seen as a streak of darker clouds in this morning's MODIS satellite image (Figure 1.) satellite loops show that Irene is beginning to recover from this adversity, with a respectable amount of heavy thunderstorms beginning to wrap around to the southwest side from the north. An upper-level wind analysis from the University of Wisconsin CIMSS site shows that Irene's upper-level outflow is much more restricted than was the case 24 hours ago. An upper-level outflow channel that was open to the south is gone, and has been replaced by shearing winds from the west and southwest that are ripping into the hurricane. I think it is 30% likely that Irene will have trouble recovering from this setback, and will not reach the peak intensity of 120 mph winds it had earlier. However, it is more likely that the hurricane will be able to re-establish its upper-level outflow and overcome the shear, based on the latest satellite loops, plus forecasts from the various hurricane models such as the GFDL, HWRF, and ECMWF, which all show Irene at Category 3 strength as it approaches North Carolina on Saturday afternoon.


Figure 1. MODIS satellite image of Hurricane Irene taken at 11:50 am EDT Thursday August 25, when Irene was a Category 3 hurricane with 115 mph winds. The eye of the storm was just off the coast of Abaco Island in the Bahamas. Note the rather squashed appearance of the hurricane, with less heavy thunderstorms on its southwest side. Upper level winds of 10 - 20 knots out of the southwest were eating away at the clouds on this side, and you can see that this shear helped drive some dry air into the hurricane, which can be seen as a darker strip of cloud spiraling into the center from the south, around the east side, then into the center along the northwest side of the storm. Image credit: a href=http://rapidfire.sci.gsfc.nasa.gov/gallery/ NASA.

Irene likely to bring destructive fresh water flooding
In this morning's post, I highlighted the threat from storm surge flooding, but flash flooding and river flooding from Irene's torrential rains are also a huge threat. The hurricane is expected to bring rains in excess of 12" to 100-mile swath from Eastern North Carolina northwards along the coast, through New York City. The danger of fresh water flooding is greatest in northern New Jersey, Southeast Pennsylvania, and Southeast New York, where the soils are saturated from heavy August rains that were among the heaviest on record. At Philadelphia, rainfall so far this August has been 13 inches, not far from the record for rainiest month of all-time, the 15.82" that fell in August 1867. This record will almost certainly be broken when Irene's rains arrive. In general, the heaviest rains will fall along the west side of the hurricane's track, and the greatest wind damage will occur on the east side. Right now, it does not appear that tornadoes will be a major concern, but there will probably be a few weak tornadoes. Hurricane Bob of 1991, the last hurricane to affect New England, spawned six tornadoes, most of them weak F-0 and F-1 twisters.


Figure 2. Predicted rainfall for the 5-day period ending at 8 am EDT Tuesday August 30, as issued by NOAA/HPC.

Latest forecast for Irene
The latest set of model runs don't show any major changes to Irene's track or intensity. Irene will bring damaging winds, torrential rains, and an extremely dangerous storm surge to the coast, affecting a huge area of the mid-Atlantic and New England. Take this storm seriously! Expect widespread disruptions to electric power, transportation, and water systems. Be prepared for many days without power, as utility crews will be overwhelmed with the damage. Irene is capable of inundating portions of the coast under 10 - 15 feet of water, to the highest storm surge depths ever recorded. I strongly recommend that all residents of the mid-Atlantic and New England coast familiarize themselves with their storm surge risk. The best source of that information is the National Hurricane Center's Interactive Storm Surge Risk Map, which allows one to pick a particular Category hurricane and zoom in to see the height above ground level a worst-case storm surge may go. If you prefer static images, use wunderground's Storm Surge Inundation Maps. If these tools indicate you may be at risk, consult your local or state emergency management office to determine if you are in a hurricane evacuation zone. Mass evacuations of low-lying areas along the entire coast of New Jersey, Delaware, Maryland, and Virginia are at least 50% likely to be ordered by Saturday. The threat to the coasts of New York, Connecticut, Rhode Island, Massachusetts, New Hampshire, and Maine is less certain, but evacuations may be ordered in those states, as well. Irene is a very dangerous storm for an area that has no experience with hurricanes, and I strongly urge you to evacuate from the coast if an evacuation is ordered by local officials. My area of greatest concern is the coast from Ocean City, Maryland, to Atlantic City, New Jersey. It is possible that this stretch of coast will receive a direct hit from a slow-moving Category 2 hurricane hitting during the highest tide of the month, bringing a 10 - 15 foot storm surge.

Links
For those of you wanting to know your odds of receiving hurricane force or tropical storm force winds, I recommend the NHC wind probability product.

Wunderground has detailed storm surge maps for the U.S. coast.

The National Hurricane Center's Interactive Storm Surge RIsk Map, which allows one to pick a particular Category hurricane and zoom in, is a good source of storm surge risk information.

Wunderblogger Mike Theiss is in Nassau, documenting the storm's impact on the Bahamas.

Jeff Masters

Hurricane

Updated: 09:02 PM GMT die 25o August, anno 2011

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Irene an extremely dangerous storm surge threat to the mid-Atlantic and New England

By: JeffMasters, 02:55 PM GMT die 25o August, anno 2011

Back in 1938, long before satellites, radar, the hurricane hunters, and the modern weather forecasting system, the great New England hurricane of 1938 roared northwards into Long Island, New York at 60 mph, pushing a storm surge more than 15 feet high to the coast. Hundreds of Americans died in this greatest Northeast U.S. hurricane on record, the only Category 3 storm to hit the Northeast since the 1800s. Since 1938, there have been a number of significant hurricanes in the Northeast--the Great Atlantic hurricane of 1944, Hazel of 1954, Diane of 1955, Donna of 1960, Gloria of 1985, Bob of 1991, and Floyd of 1999--but none of these were as formidable as the great 1938 storm. Today, we have a hurricane over the Bahamas--Hurricane Irene--that threatens to be the Northeast's most dangerous storm since the 1938 hurricane. We've all been watching the computer models, which have been steadily moving their forecast tracks for Irene more to the east--first into Florida, then Georgia, then South Carolina, then North Carolina, then offshore of North Carolina--and it seemed that this storm would do what so many many storms have done in the past, brush the Outer Banks of North Carolina, then head out to sea. Irene will not do that. Irene will likely hit Eastern North Carolina, but the storm is going northwards after that, and may deliver an extremely destructive blow to the mid-Atlantic and New England states. I am most concerned about the storm surge danger to North Carolina, Virginia, Maryland, Delaware, New Jersey, New York, and the rest of the New England coast. Irene is capable of inundating portions of the coast under 10 - 15 feet of water, to the highest storm surge depths ever recorded. I strongly recommend that all residents of the mid-Atlantic and New England coast familiarize themselves with their storm surge risk. The best source of that information is the National Hurricane Center's Interactive Storm Surge Risk Map, which allows one to pick a particular Category hurricane and zoom in to see the height above ground level a worst-case storm surge may go. If you prefer static images, use wunderground's Storm Surge Inundation Maps. If these tools indicate you may be at risk, consult your local or state emergency management office to determine if you are in a hurricane evacuation zone. Mass evacuations of low-lying areas along the entire coast of New Jersey, Delaware, Maryland, and Virginia are at least 50% likely to be ordered by Saturday. The threat to the coasts of New York, Connecticut, Rhode Island, Massachusetts, New Hampshire, and Maine is less certain, but evacuations may be ordered in those states, as well. Irene is an extremely dangerous storm for an area that has no experience with hurricanes, and I strongly urge you to evacuate from the coast if an evacuation is ordered by local officials. My area of greatest concern is the coast from Ocean City, Maryland, to Atlantic City, New Jersey. It is possible that this stretch of coast will receive a direct hit from a slow-moving Category 2 hurricane hitting during the highest tide of the month, bringing a 10 - 15 foot storm surge.


Figure 1. The scene in Nassau in the Bahamas at daybreak today. Image credit: Wunderblogger Mike Theiss.

Irene a Category 3 over the Bahamas, headed northwest
Hurricane Irene tore through the Bahama Islands overnight, bringing hurricane-force winds, torrential rains, and storm surge flooding to Crooked Island, Long Island, Rum Cay, and Cat Island, which all took a terrific pounding. Eleuthera and Abaco Island will receive the full force of Irene's eyewall today, but the eyewall will miss capital of Nassau. Winds there were sustained at 41 mph, gusting to 66 mph so far this morning, and I expect these winds will rise to 50 - 55 mph later today. Wunderblogger MIke Theiss is in Nassau, and will be sending live updates through the day today. Winds on Grand Bahama Island in Freeport will rise above tropical storm force late Thursday morning, and increase to a peak of 45 - 55 mph late Thursday afternoon. Grand Bahama will also miss the brunt of the storm. Irene is visible on Miami long-range radar, and the outer bands of the hurricane are bringing rain to Southeast Florida this morning.

Irene is currently undergoing an eyewall replacement cycle, where the inner eyewall collapses, and a new outer eyewall forms from a spiral band. During this process, the hurricane may weaken slightly, and it may take the rest of today for a new eyewall to fully form. Satellite imagery shows a lopsided pattern to Irene, with less cloud cover on the storm's southwest side. This is due to upper level winds from the southwest creating about 10 - 20 knots of wind shear along the storm's southwest side. We can hope that the shear will be strong enough to inject some dry air into the core of Irene and significantly weaken it today, but I put the odds of that happening at only 10%. The most likely scenario is that Irene will complete its eyewall replacement cycle later today or on Friday, then begin intensifying again. Wind shear is expected to stay moderate, 10 - 20 knots, for the next three days, ocean temperatures are a very warm 29°C, and Irene has an upper-level high pressure system on top of it, to aid upper-level outflow. None of our intensity forecast models show Irene growing to Category 4 strength, though the last 4 runs of the ECMWF global model--our best model for forecasting track--have intensified Irene to a Category 4 hurricane with a 912 - 920 mb pressure as it crosses over Eastern North Carolina.

Track forecast for Irene
The models have edged their tracks westwards in the last cycle of runs, and there are no longer any models suggesting that Irene will miss hitting the U.S. The threat to eastern North Carolina has increased, with several of our top models now suggesting a landfall slightly west of the Outer Banks is likely, near Morehead City. After making landfall on the North Carolina coast Saturday afternoon or evening, Irene is likely to continue almost due north, bringing hurricane conditions to the entire mid-Atlantic coast, from North Carolina to Long Island, New York. This makes for a difficult forecast, since a slight change in Irene's track will make a huge difference in where hurricane conditions will be felt. If Irene stays inland over eastern North Carolina, like the ECMWF and GFDL models are predicting, this will knock down the storm's strength enough so that it may no longer be a hurricane once it reaches New Jersey. On the other hand, if Irene grazes the Outer Banks and continues northwards into New Jersey, like the GFS model is predicting, this could easily be a Category 2 hurricane for New Jersey and Category 1 hurricane for New York City. A more easterly track into Long Island would likely mean a Category 2 landfall there.

Category 2 landfalls may not sound that significant, since Hurricane Bob of 1991 made landfall over Rhode Island as a Category 2, and did only $1.5 billion in damage (1991 dollars), killing 17. But Irene is a far larger and more dangerous storm than Bob. The latest wind analysis from NOAA/HRD puts Irene's storm surge danger at 4.8 on a scale of 0 to 6, equivalent to a borderline Category 3 or 4 hurricane's storm surge. Bob had a much lower surge potential, due to its smaller size, and the fact it was moving at 32 mph when it hit land. Irene will be moving much slower, near 18 mph, which will give it more time to pile up a big storm surge. The slower motion also means Irene's surge will last longer, and be more likely to be around during high tide. Sunday is a new moon, and tides will be at their highest levels of the month during Sunday night's high tide cycle. Tides at The Battery in New York City (Figure 3) will be a full foot higher than they were during the middle of August. Irene will expand in size as it heads north, and we should expect its storm surge to be one full Saffir-Simpson Category higher than the winds would suggest.


Figure 2. Predicted tides for the south shore of New York City's Manhattan Island at The Battery for Sunday, August 28 and Monday, August 29. High tide is near 8pm EDT Sunday night. Tidal range between low and high tide is 6 feet on Sunday, the highest range so far this month. A storm surge of 10 feet would thus be 10 feet above Mean Lower Low Water (MLLW, the lowest tide of the year), but 16 feet over this mark if it came at high tide. Image credit: NOAA Tides and Currents.

Irene's storm surge potentially extremely dangerous for the mid-Atlantic coast
Irene's large size, slow motion, arrival at high tide, and Category 3 strength at landfall in North Carolina will likely drive a storm surge of 8 - 10 feet into the heads of bays in Pamlico Sound, and 3 - 6 feet in Albemarle Sound. As the storm progresses northwards, potential storm surge heights grow due to the shape of the coast and depth of the ocean, though the storm will be weakening. If Irene is a Category 1 storm as it crosses into Virginia, it can send a storm surge of 4 - 8 feet into Chesapeake Bay and Norfolk. I give a 50% chance that the surge from Irene in those locations will exceed the record surges observed in 2003 during Hurricane Isabel. The region I am most concerned about, though, is the stretch of coast running from southern Maryland to Central New Jersey, including Delaware and the cities of Ocean City and Atlantic City. A Category 1 hurricane can bring a storm surge of 5 - 9 feet here. Irene's large size, slow movement, and arrival at the highest tide of the month could easily bring a surge one Category higher than the storm's winds might suggest, resulting in a Category 2 type inundation along the coast, near 10 - 15 feet. This portion of the coast has no hurricane experience, and loss of life could be heavy if evacuation orders are not heeded. I give a 30% chance that the storm surge from Irene will bring water depths in excess of 10 feet to the coasts of Maryland, Delaware, and New Jersey.


Figure 3. The height above ground that a mid-strength Category 2 hurricane with 100 mph winds would push a storm surge along the Maryland, Delaware, and New Jersey coasts in a worst-case scenario. The image was generated using the primary computer model used by the National Hurricane Center (NHC) to forecast storm surge--the Sea, Lake, and Overland Surge from Hurricanes (SLOSH) model. The accuracy of the SLOSH model is advertised as plus or minus 20%. This "Maximum Water Depth" image shows the water depth at each grid cell of the SLOSH domain. Thus, if you are inland at an elevation of ten feet above mean sea level, and the combined storm surge and tide (the "storm tide") is fifteen feet at your location, the water depth image will show five feet of inundation. This Maximum of the "Maximum Envelope of Waters" (MOM) image was generated for high tide and is a composite of the maximum storm surge found for dozens of individual runs of different Category 2 storms with different tracks. Thus, no single storm will be able to cause the level of flooding depicted in this SLOSH storm surge image. Consult our Storm Surge Inundation Maps page for more storm surge images of the mid-Atlantic coast.


Figure 4. The height above ground that a mid-strength Category 2 hurricane with 100 mph winds would push a storm surge along the New Jersey coast in a worst-case scenario. Water depths could reach 6 - 8 feet above ground level in Ocean City and Atlantic City, and up to 16 feet along less populated sections of the coast.

Irene's storm surge may flood New York City's subway system
The floodwalls protecting Manhattan are only five feet above mean sea level. During the December 12, 1992 Nor'easter, powerful winds from the 990 mb storm drove an 8-foot storm surge into the Battery Park on the south end of Manhattan. The ocean poured over the city's seawall for several hours, flooding the NYC subway and the Port Authority Trans-Hudson Corporation (PATH) train systems in Hoboken New Jersey. FDR Drive in lower Manhattan was flooded with 4 feet of water, which stranded more than 50 cars and required scuba divers to rescue some of the drivers. Mass transit between New Jersey and New York was down for ten days, and the storm did hundreds of millions in damage to the city. Tropical Storm Floyd of 1999 generated a storm surge just over 3 feet at the Battery, but the surge came at low tide, and did not flood Manhattan. The highest water level recorded at the Battery in the past century came in September 1960 during Hurricane Donna, which brought a storm surge of 8.36 feet to the Battery and flooded lower Manhattan to West and Cortland Streets. However, the highest storm surge on record in New York City occurred during the September 3, 1821 hurricane, the only hurricane ever to make a direct hit on the city. The water rose 13 feet in just one hour at the Battery, and flooded lower Manhattan as far north as Canal Street, an area that now has the nation's financial center. The total surge is unknown from this greatest New York City hurricane, which was probably a Category 2 storm with 110 mph winds. NOAA's SLOSH model predicts that a mid-strength Category 2 hurricane with 100-mph winds could drive a 15 - 20 foot storm surge to Manhattan, Queens, Kings, and up the Hudson River. JFK airport could be swamped, southern Manhattan would flood north to Canal Street, and a surge traveling westwards down Long Island Sound might breach the sea walls that protect La Guardia Airport. Many of the power plants that supply the city with electricity might be knocked out, or their docks to supply them with fuel destroyed. The more likely case of a Category 1 hurricane hitting at high tide would still be plenty dangerous, with waters reaching 8 - 12 feet above ground level in Lower Manhattan. Given the spread in the models, I predict a 20% chance that New York City will experience a storm surge in excess of 8 feet that will over-top the flood walls in Manhattan and flood the subway system. This would most likely occur near 8 pm Sunday night, when high tide will occur and Irene should be near its point of closest approach. Such a storm surge could occur even if Irene weakens to a tropical storm on its closest approach to New York City.


Figure 5. The height above ground that a mid-strength Category 2 hurricane with 100 mph winds would push a storm surge in a worst-case scenario in New York City.


Figure 6. Flooded runways at New York's La Guardia Airport after the November 25, 1950 Nor'easter breached the dikes guarding the airport. Sustained easterly winds of up to 62 mph hit the airport, pushing a large storm surge up Long Island Sound. The storm's central pressure bottomed out at 978 mb. Image credit: Queens Borough Public Library, Long Island Division.

The rest of New England
The entire New England coast is at high danger of receiving its highest storm surge in the past 50 years from Irene, though the exact locations of most danger remain unclear. If North Carolina takes a bullet for us and reduces Irene below hurricane strength before the storm reaches New England, the surge will probably not cause major destruction. But if Irene misses North Carolina and arrives along the New England coast as a hurricane, the storm surge is likely to cause significant damage. I urge everyone along the coast to familiarize themselves with their storm surge risk and be prepared to evacuate should an evacuation order be issued.

Links
For those of you wanting to know your odds of receiving hurricane force or tropical storm force winds, I recommend the NHC wind probability product.

Wunderground has detailed storm surge maps for the U.S. coast.

The National Hurricane Center's Interactive Storm Surge RIsk Map, which allows one to pick a particular Category hurricane and zoom in, is a good source of storm surge risk information.

Wunderblogger Mike Theiss is in Nassau, and will be sending live updates through the day today.

Landstrike is an entertaining fictional account of a Category 4 hurricane hitting New York City.

Elsewhere in the tropics
Tropical Depression Ten in the far Eastern Atlantic will not be a threat to any land areas over the next seven days, and will probably move too far north to ever be a threat to land.

Portlight mobilizes for Irene
The Bahamas have been hit hard by Irene, and unfortunately, it appears that the Northeast U.S. may have its share of hurricane victims before Irene finally dissipates. My favorite disaster relief charity, Portlight.org, is mobilizing to help, and is sending out their relief trailer and crew to the likely U.S. landfall point. Check out this blog to see what they're up to; donations are always needed.

Jeff Masters

Hurricane

Updated: 08:39 PM GMT die 25o August, anno 2011

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Hurricane Irene Prepares to Leave the Bahamas and Head for the US

By: JeffMasters, 07:51 AM GMT die 25o August, anno 2011

As of 2AM EDT, Hurricane Irene was located at 24.2N, 76.0W, 105 miles east-southeast of Nassau or 760 miles south of Cape Hatteras. It was moving northwest at 12 mph with maximum sustained winds of 115 mph, making it a Category 3 storm on the Saffir-Simpson scale. Irene has a minimum central pressure of 950 mb. Hurricane force winds can be found up to 70 miles from Irene's center, and tropical storm force winds can be found out to 255 miles from the storm's center.

Hurricane warnings are in effect for all of the Bahamas. Hurricane and tropical storm watches will likely be posted for the Carolina coastlines later this morning. At this time, Dare County Emergency Management has issued a mandatory evacuation order for all visitors in their county. Dare County Schools will also be closed Thursday and Friday.

Satellite Views
Figure 1 is the infrared satellite image of Irene at 135EDT. The convection is a bit unbalanced around the storm center, which is going to cause Irene to wobble like an unbalanced clothes washer (Analogy courtesy of Angela Fritz) over the next few hours. At the time this image was taken, the convection around Irene's center appears to be getting more vigorous, as cold cloudtops are starting to increase around the storm center. This is important to note because microwave satellite imagery from Wednesday evening suggested Irene was starting an eyewall replacement cycle. Figure 2 shows passive microwave imagery from a Air Force DMSP polar-orbiting satellite. The two concentric green/yellow bands in the image suggest that two eyewall features are present in Irene, and Hurricane Hunter observations confirm this. This has important consequences for Irene's intensity, because in an eyewall replacement cycle, as the inner eyewall weakens, the storm's intensity drops. However, once the inner eyewall is gone, and the outer eyewall contracts to replace it, the storm intensity will increase again.


Figure 1 IR satellite view of Irene taken at 113AM EDT, August 23, 2011


Figure 2 DMSP F18 microwave overpass of Irene at 824PM EDT, August 24, 2011. Image courtesy of the Naval Research Laboratory

Track Forecast

Irene is forecast to move to the northwest, passing over the northwest Bahamas by Thursday evening, then curving to the northeast. Irene then makes landfall in the US near or at the Outer Banks Saturday afternoon, then traveling along the mid-Atlantic coastline of the US. Sunday, Irene may make secondary landfall anywhere from New Jersey to Long Island and the southern New England coastline. In my opinion, New York City may be significantly impacted by Irene. It is also important to note that the windfield of Irene is expected to be large, affecting areas distant from the immediate track of Irene's center. Tropical storm forces winds are expected to be found out to at least 150 miles away from Irene's center on Friday afternoon.

NHC is forecasting for Irene to become a Category 4 storm (winds faster than 130 mph) by Thursday morning. As Irene moves northward into cooler water, the intensity is expected to drop slowly to a Category 2 storm before making landfall in the Outer Banks.


Figure 3 Official track forecast of Irene at 2AM EDT.

Forecast models and today's planned flights
The different forecast models are still in fairly good agreement about Irene's track through the Bahamas and along the east coast of the US. The 00Z GFS run is in close agreement with the 12Z ECMWF run, but the 00Z ECMWF run (shown in figure 4) is continuing the ECMWF's trend of shifting the track westward with each run. NHC forecasters have been placing emphasis on the ECMWF's forecast track when making their forecasts for IRene, so it is possible that the NHC track will shift westwards at the 5AM update.

Looking at the plan of the day valid for today, it will be a busy day for airborne reconnaissance. Three flights for the Air Force hurricane hunters, two flights for the Gulfstream IV (Gonzo), and two flights for NOAA 42, a WP-3D (Kermit). They may have to give NOAA a littering permit for all of the dropsondes used to monitor Irene and her environment, but the forecast improvements they generate are worth the effort.


Figure 4 Plot of the maximum sustained winds in mph over the next week from the 00Z ECMWF forecast.

Impacts

Hurricane force winds will arrive in the northwestern Bahamas today. Storm surge near the center of Irene will be 7-11 feet above tide level. The Bahamas can expect 6-12 inches of rain over the next day or so, and it looks like the Turks and Caicos islands will receive a total of 6-12 inches from Irene. Large, swells from Irene will start landing on the southeastern US coastline later today. Please don't go in the water, as these swells can cause dangerous rip currents. Dr. Masters has catalogued the worst-case storm surge surge scenarios as a function of storm intensity here.

In my opinion, people living from the Carolinas to Cape Cod should pay close attention to Irene and prepare for a wide range of impacts. I think that there is a 75% chance of Irene's secondary landfall will be somewhere between JFK airport and Cape Cod. That said, Irene's size will cause significant impacts for people living far from it's center.

Dr. Masters will have a new blog entry this morning, and Angela Fritz will be covering the afternoon. I'll be back on third shift tonight.

Thanks for reading,

Dr. Rob Carver

Hurricane

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Category 3 Hurricane Irene tracks northwest through the Bahamas

By: JeffMasters, 08:55 PM GMT die 24o August, anno 2011

Hurricane Irene remains a powerful category 3 this afternoon, with maximum sustained winds of 120 mph. Irene is moving northwest through the Bahamas at 12 mph, and its center has cleared the northern edge of Crooked Island. The next islands in the path of Irene are Rum Cay (population 80) and Cat Island (population 1700), which it will encounter later tonight. Irene will track northeast of Long Island (in the Bahamas) over the next 24 hours. George Town has been reporting wind gusts up to around 40 mph this afternoon, and wind speed will likely increase during the next 12 hours as Irene's center passes about 30-40 miles to their northeast. Long Island in the Bahamas will likely see category 1 winds, which begin at 74 mph. Shelters on New Providence and Grand Bahama are open and ready for business, and Grand Bahama International Airport will remain closed until Irene passes.

Irene continues to look well-organized on satellite, especially compared to yesterday afternoon. Since then, intense upward motion, and therefore strong thunderstorm activity, has encompassed the center on all sides, which has led to a well-defined eye. Throughout the morning, Irene's eye wall has shrunk, and a new eye wall could be developing, although it remains unclear at this point. If this is the case, it could lead to some temporary weakening of the hurricane, which would be good for the Bahamas. This afternoon, Irene's hurricane-force winds extend 50 miles from the center, and tropical storm-force winds extend up to 205 miles from the center. Earlier this morning, an Air Force Hurricane Hunter mission investigated Irene and a NOAA Gulfstream (Gonzo) is currently collecting data around the hurricane.


Figure 1. Microwave satellite imagery of Irene captured at 8am this morning. Image source: Naval Research Laboratory.

Track forecast for Irene
NOAA has continued dropsonde missions today, scouring the atmosphere for data as far north as the waters off of South Carolina. Every bit of upper-air data that the models can ingest will lead to better forecasts and decreased uncertainty. These missions are an investment that pay off. Irene will track through the central Bahamas today, the northwestern Bahamas on Thursday, and approach the Outer Banks of North Carolina on Friday. Beyond this there is a bit of divergence in the models. Both the GFDL and the HWRF are forecasting a landfall on Long Island, New York, and the ECMWF continues to suggest a landfall even further west than that. NOGAPS is still the eastern outlier, which misses the U.S. all together and makes landfall in Canada. Today the official track forecast from the National Hurricane Center agrees with the GFS forecast through Saturday morning, and then diverges ever so slightly to the west of that through Monday. It has become clear over the past 3 days that everyone on the East Coast from North Carolina to Maine should be prepared to feel impacts from Hurricane Irene.


Figure 2. Official track forecast provided by the National Hurricane Center.

Intensity forecast for Irene
Irene continues to be embedded in a large envelope of moisture, and wind shear is expected to remain low to moderate, 5 - 20 knots, for the next three days. With water temperatures very warm, 28 - 30°C, these conditions should allow for intensification to a category 4 hurricane (winds of 131 to 155 mph). The only reliable model that's not forecasting this intensification is the GFS, and this is likely due to its relatively course spatial resolution. The National Hurricane Center expects Irene to intensify to a category 4 tomorrow, with a decrease in intensity back to a category 3 on Friday.

Links
For those of you wanting to know your odds of receiving hurricane force or tropical storm force winds, check out the NHC wind probability product.

Wunderground has detailed storm surge maps for the U.S. coast.

Our Wundermap is also a great resource for tracking hurricanes, with the ability to turn on multiple layers of data, including satellite, official track forecast, and current weather observations from not only the U.S. but the Caribbean and Bahamas, as well. Here's a link to get you started.

Angela

Hurricane

Updated: 10:12 PM GMT die 24o August, anno 2011

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Powerful Category 3 Irene enters the Bahamas

By: JeffMasters, 03:49 PM GMT die 24o August, anno 2011

Powerful Category 3 Hurricane Irene stormed through the Turks and Caicos Islands overnight, bringing hurricane-force winds, torrential rains, and storm surge flooding. On Providenciales in the Turks and Caicos Islands, where half of the population of these islands live, winds reached a sustained 65 mph at a personal weather station at Pine Cay, and the pressure bottomed out at 989 mb. The eyewall of Irene missed the island, with the center of the storm passing about 60 miles to the southwest. The center of Irene passed about 60 miles to the northwest of Grand Inagua Island, and Category 1 hurricane conditions were probably experienced on that island. Damage in the Turks and Caicos is likely to be much less than the $50 - $200 million wrought by Category 4 Hurricane Ike of 2008, since Irene's eyewall missed populated islands.


Figure 1. Morning satellite image of Irene.

Monday, Irene hit Puerto Rico as a tropical storm with 70 mph winds, but reached hurricane strength as it emerged into the Atlantic northwest of the capital of San Juan. One drowning death is being reported from the island, and the storm dumped up to 20 inches of rain in some areas. About 11% of the island was still without power this morning, and numerous roads were closed due to flooding and landslides. Irene did an estimated $17 million in damage to agriculture and $2 million to ports in Puerto Rico. Satellite estimates suggest that Irene has brought only 1 - 2 inches of rain to Haiti. With Irene now pulling away from Hispaniola, Haiti can expect only another 1 - 2 inches from the hurricane, and appears to have dodged a major bullet. Heavy rains of 3 - 6 inches were common across the Dominican Republic, where moderate flooding but no deaths occurred.


Track forecast for Irene
Continuing dropsonde missions by the NOAA jet have helped to significantly narrow the uncertainty in the 1 - 3 day forecasts from the computer models. Irene will track through the central Bahamas today, the northwestern Bahamas on Thursday, and approach the Outer Banks of North Carolina on Friday. However, the models still diverge considerably on their 4 - 5 days forecasts, and we don't know if Irene will plow up the mid-Atlantic coast into New Jersey, as the GFDL model is predicting, hit New England between Long Island, NY and Massachusetts, as the ECMWF, GFS, and HWRF models are predicting, or miss the U.S. and hit Canada, as the NOGAPS model is predicting.

Intensity forecast for Irene
Latest data from the Hurricane Hunters shows that Irene has paused in its intensification cycle. A gap has opened in the eyewall, and the central pressure has remained constant at 956 - 957 mb over the past few hours. However, the hurricane is embedded in a large envelope of moisture, and wind shear is expected to remain low to moderate, 5 - 20 knots, for the next three days. With water temperatures very warm, 28 - 30°C, these conditions should allow for intensification to a Category 4 storm sometime in the next two days. Satellite loops show that Irene is well-organized, with excellent upper-level outflow, and impressive spiral banding.

Irene's impact on the Bahama Islands
Irene is making a direct hit on Crooked Island (population 350) in the Bahamas, and will continue west-northwest and hit Rum Cay (population 80) and Cat Island (population 1700) late tonight. These unfortunate islands will bear the full brunt of Irene's 115+ mph winds and 8 - 13 foot storm surge, and suffer major damage that will take months to recover from. Major damage is also likely on Long Island (population 3000) and San Salvador Island (population 1000.) Shortly after midnight tonight, winds at the capital of Nassau, home to 70% of the population of the Bahamas, will rise above tropical storm force, and increase through the night. By late morning on Thursday, sustained winds will peak on Nassau at just below hurricane force, 60 - 70 mph. Nassau will miss the brunt of the storm, and I expect the airport should be able to re-open on Friday. Winds on Grand Bahama Island in Freeport will rise above tropical storm force late Thursday morning, and increase to a peak of 45 - 60 mph late Thursday afternoon. Grand Bahama will also miss the brunt of the storm, but Abaco Island to its east will likely experience Category 2 hurricane conditions Thursday afternoon. However, Abaco will probably miss the right front eyewall of Irene with the strongest winds and highest storm surge.


Figure 2. Wind distibution around Irene as of 1330 UTC (9:30am EDT) August 24, 2011. Irene was a Category 3 hurricane with 115 mph winds at the time. Hurricane force winds (yellow colors) extended over Crooked Island to the storm's northwest, and over Mayaguana Island to the east. Image credit: NOAA/AOML. Irene is a large storm, and its potential storm surge damage rated 3.9 on a scale of 0 to 6, with its wind damage potential rated at 2.5 on a scale of 0 to 6.

Irene's impact on the Southeast U.S.
Long-period ocean swells from Irene will reach the coast from Florida to North Carolina tonight, and continue to build as the storm approaches. The outermost rainbands of the hurricane will reach South Florida by Thursday morning, and spread over much of the eastern coastal portion of Florida during the day Thursday. If Irene follows the official NHC forecast through the Bahama Islands, the storm's expected radius of tropical storm-force winds of 130 - 170 miles will keep tropical storm conditions just off the east coast of Florida. Sustained winds of 20 - 30 mph can be expected along the coast of Florida during Irene's point of closest approach, and rainfall amounts of 1 - 2" will be common along the coast. Georgia, which could use the rain, will get very little. It is unlikely any airport in Florida or Georgia will need to close for Irene.

Late Friday night or early Saturday morning, Irene's outer spiral bands will move over the southern coast of North Carolina and the northeastern portion of South Carolina, and tropical storm-force winds of 39+ mph will arrive. Winds will steadily increase to hurricane force on the Outer Banks by Saturday night. The main damage from Irene in North Carolina will come from the storm's flooding rains of 4 - 12" that will fall in coastal areas. Fortunately, this region is under moderate to severe drought, so the damage will not be as severe as that experienced during Hurricane Floyd of 1999. Significant wind damage can be expected in the Outer Banks of North Carolina, and considerable storm surge damage may occur along the shores of Pamlico and Albemarle Sounds. If Irene's eye misses making landfall in North Carolina, total damage from the storm should be less than $200 million, and could be considerably less than that.


Figure 3. Sea surface temperatures for August 24, 2011. Temperatures of 26°C (79°F) are typically needed for a hurricane to maintain its strength (black line). This boundary lies just off the southern coast of New Jersey this year, which is much farther north than usual.


Figure 4. Predicted 5-day rainfall for the period ending Monday morning, August 29, at 8am EDT. Image credit: NOAA/HPC.

Irene's impact on the mid-Atlantic and New England
The impact of Irene on the mid-Atlantic and New England is highly uncertain at this point, because we don't know if the core of the storm will miss the coast or not. In general, the heaviest rains will fall along a 100-mile swath just to the west of where the center tracks, and the worst wind and storm surge damage will occur to the east. If the core of Irene stays offshore, the mid-Atlantic and New England may escape with a few hundred million dollars in damage from flooding due to heavy rains and storm surge. If Irene hits Long Island or Southeast Massachusetts, the storm has the potential to be a $10 billion disaster. Irene is one of those rare storms that has the potential to make landfall in New England as a Category 2 or stronger hurricane. It is difficult for a major Category 3 or stronger hurricane crossing north of North Carolina to maintain that intensity, because wind shear rapidly increases and ocean temperatures plunge below the 26°C (79°F) level that can support a hurricane. We do expect wind shear to rapidly increase to a high 30 - 50 knots once Irene pushes north of Delaware, which should knock the storm down by at least 15 - 30 mph before it reaches New England. However, this year sea surface temperatures 1 - 3°F warmer than average extend along the East Coast from North Carolina to New York. Waters of at least 26°C extend all the way to Southern New Jersey, which will make it easier for Irene to maintain its strength much farther to the north than a hurricane usually can. During the month of July, ocean temperature off the mid-Atlantic coast (35°N - 40°N, 75°W - 70°W) averaged 2.6°F (1.45°C) above average, the second highest July ocean temperatures since record keeping began over a century ago (the record was 3.8°F above average, set in 2010.) These warm ocean temperatures will also make Irene a much wetter hurricane than is typical, since much more water vapor can evaporate into the air from record-warm ocean surfaces. The latest precipitation forecast from NOAA's Hydrological prediction center shows that Irene could dump over 8 inches of rain over coastal New England.


Figure 5. Soil moisture profiles from yesterday show that a region of very moist soils ranking in the top 1% in recorded history (dark green colors) lie over northern New Jersey, Southeast New York, and Northeast Pennsylvania. Image credit: NOAA/CPC.

Tropical storm-force winds and heavy rains will move into Eastern Virginia Saturday afternoon, and push northwards to Delaware and coastal Maryland by late Saturday night. Tropical moisture through a deep layer of the atmosphere will also stream well ahead of Irene into New England on Saturday afternoon and evening, bringing what is called a "Predecessor Rain Event" (PRE). The Washington D.C., Baltimore, and Philadelphia airports will be right at the edge of the heavy rain and high wind area, and it currently appears they will not have to close for an extended period. The Philadelphia and New York City airports may not be as lucky, and it is possible they will suffer extended closures Sunday morning and afternoon. By late Sunday night, Irene's rains will move north of New York City, allowing the airports to re-open. The highest potential for damaging fresh-water flooding is in northern New Jersey, Southeast New York, and Northeast Pennsylvania, where soil moisture is near record high levels, and there is nowhere for the rain to go (Figure 5.) Heavy rains of 4 - 12" are likely across all of coastal New England if Irene passes within 100 miles of shore.

Links
For those of you wanting to know your odds of receiving hurricane force or tropical storm force winds, I recommend the NHC wind probability product.

Wunderground has detailed storm surge maps for the U.S. coast.

Elsewhere in the tropics
A tropical wave far out in the eastern Atlantic about 200 miles southwest of the Cape Verde Islands, Invest 90L, is showing signs of organization. NHC is giving this disturbance a 50% chance of developing into a tropical depression by Friday. Several of our models do develop 90L into a tropical storm by early next week, but long-range models are showing that this system will not be a threat to any land areas over the next seven days, and will probably move too far north to ever be a threat to land.

Internet radio show on Irene at 4:30pm EDT today
I'll be discussing Hurricane Irene on a special edition of our Internet radio show, the Daily Downpour, today (Wednesday) at 4:30pm EDT. Fellow wunderground meteorologists Shaun Tanner, Tim Roche, and Angela Fritz will also be there. Listeners can email in or call in questions. The email address to ask questions is broadcast@wunderground.com.

Jeff Masters

Hurricane

Updated: 08:23 PM GMT die 26o April, anno 2012

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Hurricane Irene Approaches the Bahamas

By: JeffMasters, 07:42 AM GMT die 24o August, anno 2011

As of 2AM EDT, Hurricane Irene was located at 21.3N, 72.6W, 400 miles southeast of Nassau. It was moving west-northwest at 9 mph with maximum sustained winds of 100 mph, making it a Category 2 storm on the Saffir-Simpson scale. Irene has a minimum central pressure of 966 mb. Hurricane warnings have been issued for all of the Bahamas and the Turks and Caicos Islands. Tropical storm warnings are in effect for Haiti from Le Mole St. Nicholas to the Dominican Republic border.

Satellite Views
Figure 1 shows that Irene has a large eye visible in infrared imagery, (26 miles across accoring to a report from the Hurricane Hunters at 130AM) with well-defined outflow cirrus bands. Tuesday evening, TRMM, NASA's tropical research satellite, flew directly overhead Irene, getting a radar scan of the storm using it's downward pointing radar, shown in Figure 2. It is immediately apparent that Irene has well-developed bands of rain showers, with strong storms present in the eyewall.


Figure 1 IR satellite view of Irene taken at 113AM EDT, August 23, 2011


Figure 2 TRMM radar overpass of Irene at 713PM EDT, August 22, 2011. Image courtesy of the Naval Research Laboratory

Track Forecast

Irene is forecast to move to the northwest, passing over all of the Bahamas by Thursday evening, then curving to the north. Irene then makes landfall in the US near or at the Outer Banks Saturday afternoon, then traveling along the mid-Atlantic coastline of the US. After Saturday, Irene may pose a threat to Long Island and the New England coastline. However, NHC is quick to remind us that the average forecast error for day 4 is 200 miles, so don't stop your hurricane preparations if you aren't in the immediate area of landfall. It is also important to note that the windfield of Irene is expected to be large, affecting areas distant from the immediate track of Irene's center. Tropical storm forces winds are expected to be found out to at least 150 miles away from Irene's center on Friday afternoon.

NHC is forecasting for Irene to become a major hurricane (winds faster than 110 mph), within 24 hours.


Figure 3 Official track forecast of Irene at 2AM EDT.

Forecast models and adaptive observations
The different forecast models are in fairly good agreement about Irene's track through the Bahamas and along the east coast of the US. The GFDL, a dynamical hurricane forecasting model, which had been a western outlier from the other models is now agreeing with them. When a set of weather models using slighly different initial views of the atmosphere and slightly different ways of simulating how the atmosphere works all agree on a forecast, then meteorlogists tend to believe that the forecast is more likely to occur. The 00Z GFS and ECMWF (wind swath shown in Figure 4) forecasts are nearly identical, which furthur boosts forecaster confidence.

In the 11PM forecast discussion, the NHC forecaster praises the NOAA Gulfstream IV (aka Gonzo) for providing infomation about the atmosphere around Irene that will influence it's track. Looking at the plan of the day valid for today, it will be a busy day for airborne reconnaissance. Three flights for the Air Force hurricane hunters, two flights for the Gulfstream IV, and two flights for NOAA 42, a WP-3D (aka Kermit).


Figure 4 Plot of the maximum sustained winds in mph over the next week from the 00Z ECMWF forecast.

Impacts

In the immediate future, Irene will have a significant impact on the Bahamas and surrounding islands. Hurricane force winds are ongoing over the Turks and Caicos islands and southeastern Bahamas. These locations can expect storm surges that are 5-8 feet above tide levels. The northwestern Bahamas can expect hurricane force winds Thursday, and storm surges that are 7-11 feet above tide levels. The Turks and Caicos islands and all of the Bahamas can expect 6-12 inches of rain over the next two days.

I still think people living along the east coast of the US should closely monitor Irene and review their hurricane preparations. Irene will be a large storm, impacting areas far from the storm center track.

Dr. Masters will have a new blog entry this morning, and Angela Fritz will be covering the afternoon. I'll be back on third shift tonight.

Thanks for reading,

Dr. Rob Carver

Hurricane

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Hurricane Irene slides toward Bahamas; Strong earthquake rattles eastern U.S.

By: JeffMasters, 09:57 PM GMT die 23o August, anno 2011

Hurricane Irene is a category 1 on the Saffir Simpson scale as of 5pm EDT, with maximum sustained winds of 90 mph and a minimum central pressure of 976 mb. Irene is moving to the west-northwest at 9 mph, and continues to impact Hispaniola. Satellite imagery shows a strong rain band continuing to linger over the eastern Dominican Republic on the southeast side of Irene, but wind speeds appear to have decreased substantially in the country since this morning. Winds are gusting to around 50 mph in the Turks and Caicos Islands this afternoon. Wind shear is currently around 10-20 knots in the vicinity, which could delay intensification over the next 48 hours. The strongest winds and thunderstorm activity remain on the northwest side, and the eye that was visible on satellite earlier today has become obscured by new thunderstorm activity near the center of the hurricane. The most recent Hurricane Hunter mission found a minimum central pressure of 978 mb and a large wind field. In their 2pm EDT fix, the National Hurricane Center estimated that tropical storm-force winds extended 180 nautical miles from the center in the northeast quadrant of the hurricane. A NOAA Gulfstream plane (Gonzo) is currently flying Irene and providing dropsonde data, something that was critical in gaining model consensus yesterday. A NOAA P-3 (Kermit) is also on its way to the hurricane to provide dropsonde data, as well.


Figure 1. Satellite imagery of Hurricane Irene at 4:45pm EDT. Image credit: NOAA.

Track forecast for Hurricane Irene
Models are in better agreement on the track forecast for Irene today, although the GFDL and HWRF continue to be the western outliers. Both of these models are forecasting Irene to make landfall near the Outer Banks of North Carolina on an almost due north track. The rest of the global models continue to slide every so slightly east in their forecast track, with some not making landfall until the hurricane is as far north as Long Island. This afternoon, the ECMWF, which has been performing well this season, forecasts Irene to brush the Outer Banks before sliding up the east coast toward New York. The official track forecast from the National Hurricane Center is similar this afternoon. They're expecting Irene to take a more central track through the Bahamas over the next 48 hours and make contact with the Outer Banks on Saturday afternoon, with a second landfall in New Jersey on Sunday afternoon. Again, it's critical to note that the errors in the track forecast 4 and 5 days out are quite large, and also that the consensus in the models over the past couple of days has been to nudge the track eastward, which can be seen in this track graphic archive.

Intensity forecast for Hurricane Irene
Despite the slight weakening that happened today, Irene is still expected to reach major hurricane status (category 3+) in the next 36 hours as it moves away from the Greater Antilles and into warm "open" water. The models tend to agree on a maximum intensity of category 3, however, the GFDL is the upper outlier, and is suggesting a category 4 on Friday. The intensity forecast from the National Hurricane Center is a wind speed increase to 125 mph (category 3) by Thursday. Irene will surely be a very intense hurricane by the time it nears the Mid-Atlantic.

Magnitude 5.8 earthquake rattles eastern U.S.

A relatively large and shallow earthquake struck the Mid-Atlantic just before 2pm EDT this afternoon, and shaking was felt up and down the east coast and as far west as Ohio. According to the United States Geological Survey (USGS), the epicenter was located 5 miles southwest of Mineral, Virginia, and was 3.7 miles deep—a very shallow earthquake. Buildings were evacuated all over the Mid-Atlantic, including the Pentagon, the White House, and NCEP, but have since been reopened. The National Cathedral in Washington D.C. was apparently significantly damaged in the earthquake. National Mall monuments and memorials have closed for the afternoon. Light aftershocks have been reported by people in the region, and the USGS has reported at least one aftershock (a 2.8 in magnitude).


Figure 2. "Did you feel it?" map from the USGS. Shaking reports from today's earthquake can be submitted to the USGS here.

This earthquake appears to be the strongest to occur in Virginia since May 31, 1897, when a magnitude 6 (approximately) struck Giles County. Reportedly, shaking was felt from Georgia to Pennsylvania and west to Indiana and Kentucky, which is an area that covers approximately 725,000 square miles. It's likely that this quake will have a similar extent when all the reports come in.

Angela

Earthquake Hurricane

Updated: 09:59 PM GMT die 23o August, anno 2011

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Irene pounds the Dominican Republic, heads for the Bahamas

By: JeffMasters, 03:32 PM GMT die 23o August, anno 2011

Hurricane Irene is pounding the north coast of the Dominican Republic this morning with tropical storm-force winds and torrential rains, as the storm continues to head west-northwest towards the Bahama Islands. Puerto Plata on the north coast of the Dominican Republic reported sustained winds of 58 mph at 5am local time this morning, with heavy rain. In the Turks and Caicos Islands ahead of Irene, winds have gusted to 42 - 49 mph this morning on Providenciales at personal weather stations at the Regent Grand and at Pine Cay. The latest hurricane hunter eye report at 10:38am EDT found a central pressure of 980 mb, and top surface winds of 85 mph using their SFMR instrument. The plane had not finished sampling the storm yet.

Yesterday, Irene hit Puerto Rico as a tropical storm with 70 mph winds, reaching hurricane strength as it emerged into the Atlantic northwest of the capital of San Juan. No deaths or major injuries have been reported thus far from the islands, though the storm knocked out power to 1 million residents of Puerto Rico, including the entire island Vieques; 28% of Puerto Rico had no running water Monday afternoon. Billionaire Richard Branson's 8-bedroom mansion on private Necker Island in the British Virgin Islands was hit by lightning during the storm and burned down, and Branson relates on his blog how actress Kate Winslett had to carry out his 90-year-old mother from the main house to safety. Haiti has thus far escaped heavy rains from Irene, though the main danger comes today as the storm makes its closest approach to Haiti.


Figure 1. Morning satellite image of Irene, showing a hint of an eye starting to pop out.

Track forecast for Irene
Yesterday's dropsonde mission by the NOAA jet helped significantly narrow the uncertainty in the 1 - 3 day forecasts from the computer models. Irene will track through the Turks and Caicos islands today, the central Bahamas on Wednesday, and northwestern Bahamas on Thursday. However, the models still diverge considerably on their 4 - 5 days forecasts. One reliable model, the UKMET, takes Irene into South Carolina, while several others have the hurricane missing the Southeast U.S. completely, passing just offshore of the Outer Banks of North Carolina on Saturday. The official NHC forecast of a landfall along the North Carolina coast is a reasonable compromise, though with the models trending more eastwards of late, I would favor a landfall farther east than NHC is predicting. Irene will continue north or curve northeast after its encounter with North Carolina, and the hurricane could be a dangerous and destructive storm for the entire mid-Atlantic and New England coast.

A research project funded by NOAA known as the Joint Hurricane Testbed has produced a remarkable number of tools now in operational use at the National Hurricane Center to improve hurricane forecasts and warnings. One of these projects, called "Prediction of Consensus TC Track Forecast Error and Correctors to Improve Consensus TC Track Forecasts", was an effort by Dr. Jim Goerss at the Navy Research Lab to improve the accuracy of the NHC "cone of uncertainty" (AKA the "Cone of Death") showing where a storm is expected to track 2/3 of the time. The radius of the circles that make up the cone are based on error statistics of the official NHC forecast over the past five years. We can expect in certain situations, such as when the models are in substantial disagreement, a consensus forecast made using these models will have much greater than average errors. Since the NHC typically bases their forecast on a consensus forecast made using a combination of reliable hurricane forecasting models, it is instructive to view the "GPCE" (Goerss Prediction Consensus Error) circles to see if the uncertainty cone should be smaller or larger than usual. The consensus forecast I'll look at is called "TVCN", and is constructed by averaging the track forecasts made by most of (or all) of these models: GFS, ECMWF, NOGAPS, GFDL, HWRF, GFDN, and UKMET. In the case of this morning's 12 UTC (8am EDT) runs of these models, here is what the radius of the "cone of uncertainty" should be, in nautical miles:

12 hours: 27 nm
24 hours: 44 nm
36 hours: 64 nm
48 hours: 81 nm
72 hours: 137 nm
96 hours: 201 nm
120 hours: 308 nm

And here is the radius of NHC's "cone of uncertainty" for their official forecast, based on the average errors for the past five years:

12 hours: 36 nm
24 hours: 59 nm
36 hours: 79 nm
48 hours: 98 nm
72 hours: 144 nm
96 hours: 190 nm
120 hours: 239 nm

So, the GPCE error estimates are showing that the latest forecasts for Irene are better than average over the 1 - 3 day time period, and worse than average for 4 - 5 days. Note the error estimate of 308 nm (355 miles) for today's 5-day forecast. That's more than the distance from New York City to Boston, suggesting that we really don't know what portions of New England might be at most risk from Irene. It is still quite possible the core of the hurricane could miss New England.

Intensity forecast for Irene
Latest microwave data suggests that Irene does not have full eyewall; a gap exists in the southwest side. With wind shear now a moderate 10 - 20 knots, Irene may have trouble intensifying today. The hurricane is embedded in a large envelope of moisture, and wind shear is expected to remain moderate, 10 - 20 knots, for the next four days. With water temperatures very warm, 29 - 30°C, these conditions should allow for intensification to a Category 3 storm sometime in the next two days. Satellite loops show that Irene is steadily growing in size, which will protect the storm against major disruption by wind shear. The storm is lacking much development on its southwest side, where the presence of Hispaniola is interfering with development. Once Irene pulls away from Hispaniola tonight, intensification is more likely.

Irene's impact on the Turks and Caicos Islands
Heavy rains from Irene have already reached the Turks and Caicos Islands, which form the southeastern portion of the Bahama Islands chain. The last hurricane to affect the Turks and Caicos islands was Hurricane Ike of 2008. Ike's northern eyewall devastated Grand Turk, Salt Cay, South Caicos, and a few other smaller cays when the storm was at Category 4 strength. Ike then weakened slightly to a Category 3 storm with 125 mph winds before making a direct hit on Great Inagua Island. Approximately 70-80% of the houses on Great Inagua Island sustained roof damage, and 25% had major damage or were destroyed. The Morton Salt factory on the island was forced to halt operations as Ike damaged its offices and loading docks. A few West Indian flamingos were killed by Ike but most of the 50,000 flamingos in Inagua National Park--the world's largest colony--survived by taking shelter within the park's mangroves or flying to other islands. Risk Management Solutions estimates that total damage costs are between $50 and $200 million (USD) for the Turks and Caicos and the Bahamas. Irene will be weaker than Ike, so will not do as much damage. The main threat from Irene will be wind damage.


Figure 2. The path of Hurricane Ike of 2008 took it through the Turks and Caicos Islands as a Category 4 hurricane with 135 mph winds (pink colors).

Irene's impact on the Bahama Islands
Irene will pass through the length of the Bahama Island chain and cause widespread destruction on those islands unfortunate enough to encounter the storm's right front eyewall. Currently, it appears that Crooked, Cat, Exuma, Eleuthera, and Abaco Islands are all in danger of experiencing the eyewall of Irene, which will be capable of bringing storm surges of 9 - 13 feet. The current forecast puts the Bahamas' two most developed islands--New Providence and Grand Bahama--on the weaker west side of Irene, where Category 1 hurricane winds are likely. These winds will likely cause considerable but not devastating damage. Irene will come very close to the capital city of Nassau on New Providence Island on Thursday morning, home to 70% of the population of the Bahamas. Nassau has received direct hits from three major hurricanes since 1851--the Category 4 Nassau Hurricane of 1926, which killed 287 people, a Category 4 hurricane in 1866 that killed 387 people, and a Category 3 hurricane in August 1949. The island is vulnerable to high storm surges--a ten-foot storm surge is theoretically possible on the south shore of Nassau in a Category 3 hurricane. However, the south shore of the island is relatively undeveloped, and the city of Nassau and Paradise Island are mostly higher than ten feet in elevation. A much higher storm surge of 20 feet is possible along the southwest shore of Exuma Island, but again, this shore is not heavily developed.


Figure 3. The height above ground that a mid-strength Category 3 hurricane with 120 - 125 mph winds would push a storm surge in a worst-case scenario. The image was generated using the primary computer model used by the National Hurricane Center (NHC) to forecast storm surge--the Sea, Lake, and Overland Surge from Hurricanes (SLOSH) model. The accuracy of the SLOSH model is advertised as plus or minus 20%. This "Maximum Water Depth" image shows the water depth at each grid cell of the SLOSH domain. Thus, if you are inland at an elevation of ten feet above mean sea level, and the combined storm surge and tide (the "storm tide") is fifteen feet at your location, the water depth image will show five feet of inundation. This Maximum of the "Maximum Envelope of Waters" (MOM) image was generated for high tide and is a composite of the maximum storm surge found for dozens of individual runs of different Category 3 storms with different tracks. Thus, no single storm will be able to cause the level of flooding depicted in this SLOSH storm surge image.

Irene a potential multi-billion dollar disaster for New England and the mid-Atlantic
Though it is still possible the core of Irene will miss the U.S., the current NHC official forecast would mean that Irene would bring destructive flash flooding, significant beach damage, and widespread power outages due to tree damage along the entire U.S. coast from North Carolina to Maine, costing several billion dollars. If Irene ends up skirting the Outer Banks of North Carolina and not significantly weakening, then plowing through the mid-Atlantic and New England states as a Category 1 or 2 hurricane, it could become one of the ten most damaging hurricanes in history. The latest 06Z (2am EDT) run of the GFS model puts Irene ashore in Southeast Massachusetts on Sunday afternoon as a large storm with a central pressure of 974 mb. The latest run of the ECMWF model has Irene with a central pressure of 964 mb over Chesapeake Bay, and 972 mb over New Jersey. These central pressures correspond to strong tropical storm or Category 1 hurricane strengths, and are similar to what Hurricane Floyd or 1999 had when it moved up the mid-Atlantic coast after hitting North Carolina as a Category 2 hurricane. Floyd was the 14th most damaging hurricane in history, with total damages estimated at $9.2 billion (2010 dollars.) Most of the damage was in North Carolina, which experienced its worst flooding on record. If the GFS and ECMWF models are correct, Irene could easily be a $10 billion hurricane, causing widespread damage along a long section of heavily populated coast. The most damaging Northeast U.S. hurricane of all time was Hurricane Agnes of 1972, with damages estimated at $11.8 billion (2010 dollars.) Currently, it appears that Irene will hit North Carolina on Saturday, and New England on Sunday. I strongly urge all residents of the coast from North Carolina to Massachusetts to assess their hurricane preparedness immediately, and anticipate the possibility of hurricane conditions this weekend.

Links
For those of you wanting to know your odds of receiving hurricane force or tropical storm force winds, I recommend the NHC wind probability product.

Wunderground has detailed storm surge maps for the U.S. coast.

Elsewhere in the tropics
There are two tropical waves far out in the eastern Atlantic, Invest 90L and Invest 98L, that NHC is giving 20% chances of developing into tropical depressions by Thursday. At present, the long-range models are showing that both of these disturbances will not be a threat to any land areas over the next seven days, and will probably move too far north to ever be a threat to land.

Texas/Oklahoma heat wave sets all-time 100° records
The unprecedented heat wave gripping Texas and Oklahoma set several new all-time heat records yesterday. The high temperature hit 101° at the Houston Intercontinental Airport yesterday, the 22nd consecutive day of 100°+ heat and 33rd day of 100°+ heat in the city. Both are all-time records for the city. Oklahoma City recorded its 51st day of 100°+ temperatures yesterday, breaking the record for most such days in year, set previously in 1980. Temperature records for Oklahoma City date back to 1891.

Jeff Masters

Updated: 04:49 PM GMT die 23o August, anno 2011

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Category 2 Irene Approaches The Bahamas

By: JeffMasters, 07:51 AM GMT die 23o August, anno 2011

As of 2am EDT, Hurricane Irene was located at 20.1N, 69.7W, 135 miles southeast of Grand Turk Island. It was moving west-northwest at 12 mph with maximum sustained winds of 100 mph, making it a Category 2 storm on the Saffir-Simpson scale. Irene has a minimum central pressure of 978 mb. Hurricane warnings have been issued for the northern coast of the Dominican Republic from the Haiti board to Cabo Engano, the southeastern and central Bahamas, and the Turks and Caicos islands. Hurricane watches have been posted for the north coast of Haiti from Le Mole, St. Nicholas to the Dominican border and the northwestern Bahamas. Tropical storm warnings are in effect for all of Haiti and the southern coast of the Dominican Republic from Cabo Engano to Santo Domingo.

5AM Update
As of 5am EDT, Hurricane Irene was located at 20.3N, 70.1W, 105 miles southeast of Grand Turk Island. It was moving west-northwest at 12 mph with maximum sustained winds of 100 mph, keeping it a Category 2 storm on the Saffir-Simpson scale. Irene has a minimum central pressure of 978 mb.

Figure 1 shows that Irene is maturing into a vigorous storm, with apparent waves in the western edge of the cirrus outflow.


Figure 1 IR satellite view of Irene taken at 135AM EDT, August 22, 2011

Track Forecast

Irene is forecast to move to the north-northwest, passing over all of the Bahama islands by Thursday evening, at which points it starts curving to the north. Irene is forecast to make landfall in the US near Wilmington, NC Saturday evening. However, it is important to note that this is not a definitive forecast, the average forecast error for day 5 is 250 miles. The timing of Irene's recurvature depends on how quickly several small troughs of low pressure in the Northeastern US move to the east. After Saturday, Irene may pose a threat to the mid-Atlantic coastline and locations further north, but it is too early to make a skillful forecast for those regions.

NHC is forecasting for Irene to become a major hurricane (winds faster than 110 mph), within 24 hours, then reaching peak intensity at 130 mph (Category 4 storm) by 8pm EDT Thursday evening.

Forecast models and adaptive observations
The different forecast models are in rough agreement until Irene nears the Carolinas. The dynamical hurricane forecasting models, GFDL and HWRF, have Irene making landfall near Charleston, SC. NGFDL (a variant of the GFDL that uses NOGAPS for background conditions) has landfall near Morehead City, NC, and the GFS has Irene crossing the Outer Banks. The UKMET forecast track splits the difference, placing Irene near Myrtle Beach, SC at landfall.

To reduce the model spread, and improve the track forecast error, the NOAA Gulfstream IV and an Air Force WC-130J have been flying dropsonde missions north of Irene. A dropsonde is an meteorological instrument package dropped from a plane that can tell you the vertical profile of temperature, pressure, moisture, and winds. By flying these missions, the dropsondes can improve all of the numerical weather prediction models initial picture of the atmospheres, which improves the forecast. Also, NHC has asked NWS offices in the southeastern US that launch weather balloons to do so every 6 hours instead of the normal 12 hour frequency.


Figure 2 Official track forecast of Irene as of 2am.

5AM update
The 00Z ECMWF forecast is available and Figure 3 shows the maximum wind speed over the next week for the eastern coast of the US. Green indicates tropical storm force winds, while yellow and orange are hurricane-force winds. The important thing is not to fixate on the predicted landfall location, but to see that Irene's winds will affect areas far away from landfall. The GFS, not shown, agrees with ECMWF that Irene will have a large area of tropical-storm force winds associated with it.

Figure 3 Maximum wind-speed in mph from the 00Z August 23 ECMWF forecast for the next week.

Impacts

In the immediate future, Irene is expected to have a significant impact on the Bahamas and surrounding islands. Hurricane force winds are forecast to reach the southeastern Bahamas and the Turks and Caicos sometime this afternoon or evening. These locations can also expect 5-10 inches of rain. Three to six inches of rain are forecast over northern Hispaniola, with isolated areas receiving up to 10 inches. This could lead to flash flooding and mudslides in mountaineous terrain. NHC is predicting a storm surge of 9-13 feet above normal tide level for the southeastern Bahamas and the Turks and Caicos.

Outside of the islands immediately impacted by Irene, it is my judgement that everybody living on the eastern coast of the US should monitor Irene and review their hurricane preparations over the next few days.

Dr. Masters will have a new blog entry this morning, and Angela Fritz will be covering the afternoon. I'll be back on third shift tonight.

Thanks for reading,

Dr. Rob Carver

Hurricane

Updated: 09:49 AM GMT die 23o August, anno 2011

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Hurricane Irene continues to become better organized, takes aim at Bahamas

By: JeffMasters, 09:12 PM GMT die 22o August, anno 2011

Hurricane Irene remains a category 1 on the Saffir Simpson hurricane wind scale, and continues to be a U.S. landfall threat for anywhere from southern Florida to North Carolina. In the 5pm EDT update from the National Hurricane Center, Irene had maximum sustained winds of 80 mph. Irene is moving west-northwest at 13 mph along the northern Hispaniola coastline. Estimates from radar suggest Puerto Rico has seen anywhere from 1 to 5 inches of rain from Irene so far, with the heaviest rain probably being enhanced by topography. Satellite imagery shows a new burst of intense thunderstorm activity began near the center of the hurricane this afternoon, and despite land interaction, Irene continues to become larger and better organized, with tropical storm-force (39 mph) winds extending 160 miles away from the center on the northeast side of the hurricane. The latest Hurricane Hunter mission found maximum sustained winds just above 80 mph, with a minimum central pressure of 988 millibars. The strongest winds continue to be found on the north side of the storm. Another Hurricane Hunter mission is scheduled for this evening, and a NOAA Gulfstream is on its way to Irene as I type.


Figure 1. True-color image of Hurricane Irene taken at 11:20am EDT Monday August 22, 2011, shortly after Irene moved off the coast of Puerto Rico. At the time, Irene was a Category 1 hurricane with 80 mph winds. Image credit: NASA.

Track forecast for Irene
The models agree that the center of Irene will stay north of Hispaniola, which will allow the storm to continue to organize. The question that remains is how the trough of low pressure, which is expected to move across the Eastern U.S. on Wednesday and Thursday, will affect Hurricane Irene. The timing and strength of this trough, as well as the intensity of the hurricane, will determine just how quick Irene will turn away from the U.S. coast, if at all. This afternoon, the GFDL has finally started to inch its forecast track to the east, with a landfall in southern Florida. Both the HWRF and the UKMET models are suggesting a landfall in South Carolina, and the ECMWF and the GFS are forecasting a brush with the Outer Banks of North Carolina. The official forecast from the National Hurricane Center is a track north of Hispaniola over the next 24 hours, and through the Bahamas Wednesday and Thursday. While the center of the Hurricane Center's cone of uncertainty has Irene making landfall near the North Carolina/South Carolina border, it's important to note that the error in 4 and 5 day track forecasts remains high—around 200 miles in either direction. The official track has nudged a bit east since this morning, which reduces the threat to southern Florida, but increases the threat to the Carolinas.

Intensity forecast for Irene
The environment around Hurricane Irene remains moist, and wind shear is expected to remain relatively low (5 to 15 knots) along its forecast path over the next 5 days. Sea surface temperatures are certainly warm enough (29-30°C) to support intensification to a major hurricane (category 3+). Irene is still disorganized on its south side due to land interaction and dry air, but recent satellite imagery suggests increasing outflow at high levels to the south of the center, which is necessary for the hurricane to intensify. Both the GFS and the ECMWF are forecasting Irene to develop into a very large and intense hurricane. The National Hurricane Center expects Irene to intensify to a category 2 hurricane tomorrow evening as it moves away from Hispaniola. Beyond that, Irene will most likely intensify into a category 3 major hurricane with maximum sustained winds around 110 mph. Like Jeff said this morning, however, Irene could just as easily remain a category 2, or even reach category 4 wind speeds. In any case, Irene will be a powerful hurricane and a serious threat to the Bahamas and the East Coast of the United States.

Angela

Hurricane

Updated: 06:57 PM GMT die 09o January, anno 2012

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Hurricane Irene pounds Puerto Rico, heads for Hispaniola

By: JeffMasters, 02:40 PM GMT die 22o August, anno 2011

Hurricane Irene strengthened into the season's first Atlantic hurricane at 5am EDT this morning as the eye moved over San Juan, Puerto Rico, and crossed into the ocean just north of the island. Overnight, Irene held its own as the eye passed over the most mountainous portion of Puerto Rico, the El Yunque region. Winds in the higher mountains likely reached Category 2 strength, 96 - 110 mph, according to measurements from the San Juan Terminal Doppler Radar, and the hurricane pounded the island with damaging winds and flooding rains, resulting in widespread tree damage and power failures that hit 800,000 people. The San Juan Airport recorded top winds of 41 mph, gusting to 55 mph, and 2.87" of rain, as of 9am AST. Tropical storm conditions affected the Virgin Islands, with St. Thomas recording sustained winds of 40 mph, gusting to 67 mph, and 4.03" of rain as of 6am AST today. At 7am EDT, the ship Horizon Trader measured sustained northeast winds of 69 mph and wave heights of 11.5 feet at 19°N, in the northern eyewall of Irene. Latest observations from an Air Force hurricane hunter aircraft indicate that Irene is slowly intensifying, with a central pressure of 989 mb observed at 9:42am EDT. The eyewall is not fully formed yet, with a gap on the south side. This gap will need to close off before the hurricane can undergo rapid intensification.


Figure 1. A direct hit: the center of Hurricane Irene passed directly over the Terminal Doppler Radar at San Juan, Puerto Rico between 4am and 5am AST this morning.

Track forecast for Irene
The computer models show good agreement that Irene will pass along the north coast of Hispaniola today, but just a slight wobble in Irene's track to take it farther offshore--or push it onshore, over the mountains--will have major impacts on the ultimate path and strength of the hurricane. A trough of low pressure is expected to move across the Eastern U.S. on Wednesday and Thursday, turning Irene more to the northwest by Wednesday. The timing and strength of this trough varies considerably from model to model, and will be critical in determining where and when Irene will turn to the north. Irene's strength will also matter--a stronger Irene is more likely to turn northward earlier. The most popular solution among the models is to take Irene to the northwest through the Bahamas on Wednesday and Thursday, then into the Southeast U.S. coast in South Carolina or North Carolina on Saturday. Irene would then travel up the mid-Atlantic coast, arriving near Long Island, New York on Monday morning as a strong tropical storm or Category 1 hurricane. One of the models proposing this solution is our best model, the ECMWF. However, we have two other of our very good models suggesting a landfall near Miami on Thursday night is likely (the GFDL and UKMET models.) NHC forecaster Stacy Stewart gave some good reasons in this morning's discussion to favor a track close to the east coast of Florida, but just offshore. Last years' worst performing major the model, the NOGAPS, predicts that Irene will pass out to sea, missing the Southeast U.S. coast. Keep in mind that the average error of a 4-day forecast from NHC is 200 miles, and just a small deviation in the path of a storm moving roughly parallel to the coast will make a huge difference in where it ultimately makes landfall. The NOAA jet will be flying its first dropsonde mission into Irene today, which should result in a more reliable set of model runs first thing Tuesday morning.

Intensity forecast for Irene
Irene is embedded in a large envelope of moisture now, and wind shear is expected to remain low, 5 - 10 knots, for the next five days. With water temperatures very warm, 29 - 30°C, these conditions should allow for intensification except when land is interfering. Satellite loops show that Irene is steadily growing in size, which will protect the storm against major disruption by its passage along the north shore of Hispaniola today. The storm is lacking much development on its southwest side, where dry air is interfering with development. This dry air may help keep southern portions of the Dominican Republic and Haiti from receiving more than 3 - 6 inches of rain. There is at least a 30% chance that passage of the eye over Hispaniola will reduce Irene to a tropical storm tonight and into Tuesday. Due to Hispaniola blocking inflow of moist air from the south, Irene will likely compensate by building an even larger region of heavy thunderstorms to the north, offshore. Thus, when Irene's center finally moves well away from the coast on Tuesday, it will be a bigger storm, with the potential to spread hurricane conditions over a wider area later in the week when it intensifies. One limiting factor for intensification may be in the upper-level outflow pattern. The hurricane is lifting a huge amount of air from the surface to the upper atmosphere, and all that mass has to be efficiently transported away in order for the hurricane to intensify. Right now, upper level outflow is only well-established to the north and east, and the forecast outflow pattern for the coming five days is only moderately favorable. Overall, I think the official NHC forecast of a Category 3 hurricane by Thursday is the right one, though Irene could easily be a Category 2 or Category 4 storm.

Irene's impact on the Dominican Republic
Heavy rains from Irene have already reached the eastern tip of the Dominican Republic, where Punta Cana has seen wind gusts up to 29 mph this morning. The northeast coast of the country near Samana will receive the worst of Irene's wrath, with sustained winds of 50 - 70 mph and gusts above hurricane force likely to cause widespread tree damage and power outages today. Passage along the coast of the island may weaken Irene to a tropical storm by Tuesday morning, and wind damage in Puerto Plata may be less severe than at Samana. The capital of Santo Domingo will see lesser winds, perhaps 30 - 50 mph, with gusts to 60 mph. The main danger to the Dominican Republic will be Irene's torrential rains, which are likely to reach 20 inches in some mountainous regions, causing dangerous flash floods and mudslides.

Irene's impact on Haiti
No nation in the Caribbean is more vulnerable to hurricanes than Haiti, whose northern reaches are expected to receive torrential rains of 5 - 10 inches from Irene. During the 2008 hurricane season, four storms--Fay, Gustav, Hanna, and Ike--dumped heavy rains on Haiti, leaving over 1,000 people dead or missing. The path and intensity of Hurricane Irene are very similar to that of Hurricane Jeanne of 2004, which dumped 13 inches of rains on the nation's northern mountains. The rugged hillsides, stripped bare of 98% of their forest cover thanks to deforestation, let flood waters rampage into large areas of the country, killing over 3000 people, mostly in the town of Gonaives, the nation's 4th largest city. Jeanne ranks as the 12th deadliest hurricane of all time on the list of the 30 most deadly Atlantic hurricanes, and Irene's rains are capable of causing a similar disaster. During 2004 and again this year, ocean temperatures off the coast of Haiti were 1 - 1.5°C above average, one of the top five values seen in the past 100 years. Since more water vapor evaporates into the air from record warm waters, the potential for devastating floods from hurricanes is much higher in these situations. However, satellite images of Jeanne show the storm had much more moisture on its south side when it hit Hispaniola than Irene currently has, so I am hopeful that Irene's rains will not be as intense as Jeanne's were.


Figure 2. Track of Hurricane Jeanne of 2004, which followed a path very similar to what is expected from Hurricane Irene along the north coast of Hispaniola. Irene is not going to do a big loop like Jeanne did, though.

As bad as the hurricanes of 2004 and 2008 were, the January 2010 earthquake was far worse. Up to 316,000 may have been killed, and the capital city of Port-Au-Prince was devastated, leaving over 1.5 million people living under tarps during the 2010 hurricane season. Fortunately, Hurricane Tomas missed making a direct hit on Haiti, and Haiti escaped major loss of life during the 2010 hurricane season. This year, approximately 595,000 Haitians still live underneath tarps outdoors thanks to the earthquake, and these unfortunate people will be at risk of being swept away by flash flooding from Irene's torrential rains. However, Port-Au-Prince lies to the south of where Irene's main rains will fall, and I doubt the earthquake refugee camps will suffer from a major flooding disaster.


Figure 3. Hospital admissions (black bars) and death rate in percent (red line) for Haiti's cholera epidemic of 2010 - 2011. The cholera epidemic surged out of control after Hurricane Tomas dumped heavy rains on Haiti on November 4, 2010, with hospitalizations increasing by a factor of three for over a month. Over 3% of all people who contracted cholera died after Tomas' rains. However, sanitation and medical care improved in the following months, and the death rate fell by a factor of five to 0.7% by the summer of 2011. Another surge in cholera cases occurred in June 2011, doubling after heavy rainy season rains occurred. Cholera deaths doubled during the surge, but the death rate remained constant at 0.7%. Image credit: Pan American Health Organization.

Another danger is that Irene's rains will worsen the cholera epidemic that surfaced after the earthquake. Cholera is a water-borne disease, and spreads readily after heavy rains. As of August 12, 2011, the 2010 - 2011 cholera epidemic had infected 419,000 Haitians, killing 5,968. After Hurricane Tomas passed on November 5, 2010, cholera cases exploded, with hospital admissions more than tripling for over a month. Similarly, heavy rains in June 2011 during the country's usual rainy season caused doubled cholera cases and deaths for several weeks. We can expect that Irene's rains will cause at least a doubling of cholera cases for a month or more. This will lead to several hundred additional cholera deaths, given the disease's 0.7% mortality rate this summer in Haiti (during June and July 2011, 95,212 cases were reported, with 626 deaths.) An increase in cholera deaths due to Irene's rains is also a concern in the Dominican Republic, where cholera has sickened 14,000 people and killed 92 as of the end of July.

Organizations Active in Haitian Relief Efforts:
Portlight disaster relief
Lambi Fund of Haiti
Haiti Hope Fund
Catholic Relief Services of Haiti

Links
For those of you wanting to know your odds of receiving hurricane force or tropical storm force winds, I recommend the NHC wind probability product.

Wunderground has detailed storm surge maps for the U.S. coast.

See my 2010 post, Haiti's tragic hurricane history.

An exceptionally active of hurricane season
Hurricane season is only one-third over, and we've already had almost a full years' activity already. Tropical Storm Irene is the 9th named storm this year, and an average season has just 10 - 11 named storms. Irene's formation date of August 20 ties 2011 with 1936 as the 2nd earliest date for formation of the season's 9th storm. Only 2005 was more active this early. However, the first eight storms of the year have done far less damage than is typical. All eight storms stayed below hurricane strength, making 2011 the first hurricane season since record keeping began in 1851 to have more than six consecutive tropical storms that did not reach hurricane strength. As I discussed in Friday's post, a major reason for this is the lack of vertical instability over the tropical Atlantic so far this year. We've had a large amount of dry, sinking air over the tropical Atlantic, and the usual amount of dry, dusty air from the Sahara, both helping to keep the atmosphere stable and stop this year's storms from intensifying into hurricanes. Hurricane activity typically ramps up big-time by August 20, with more than 80% of all the hurricanes and 65% of all the tropical storms occurring after that date. At our current pace, 2011 will become the second busiest Atlantic hurricane season on record, with 24 - 27 named storms. There are only 21 names in the list of names for a hurricane season, so we may have to break out the Greek alphabet again in late October this year, as occurred in 2005. Ironically, this was the last time the current set of names was used in the Atlantic, so 16 of this year's 21 names are repeats of 2005. I'm not too happy about seeing another hurricane season challenge the Hurricane Season of 2005 in any way, and let's hope we don't retire another five names this year, like occurred in 2005! With vertical instability much lower this year than in 2005, and that year having already seen one storm (Dennis) retired by this point in the season, I doubt that will happen, though.


Figure 4. The annual cycle of average hurricane frequency in the Atlantic. Historically, about 35% of all the tropical storms and 15% of all the hurricanes will have occurred by August 20.

Which model should you trust?
Wunderground provides a web page with computer model forecasts for many of the best-performing models used to predict hurricane tracks. So which is the best? Well, the best forecasts are made by combining the forecasts from three or more models into a "consensus" forecast. Over the past decade, NHC has greatly improved their forecasts by relying on consensus forecast models made using various combinations of the GFS, GFDL, NOGAPS, UKMET, HWRF, and ECMWF models. If you average together the track forecasts from these models, the NHC official forecast will rarely depart much from it, and the NHC forecast has been hard to beat over the past few years. The single best-performing model over the past two years has been the ECMWF (European Center model). This model out-performed the official NHC forecast in 2010 for 1-day, 2-day, 3-day and 4-day forecasts, and in 2009 for 4-day and 5-day forecasts. You can view ECMWF forecasts on our wundermap with the model layer turned on. The European Center does not permit public display of tropical storm positions from their hurricane tracking module of their model, so we are unable to put ECMWF forecasts on our computer model forecast page that plots positions from the other major models. As seen in Figure 5, over the past two years, the GFS and GFDL model have been the next best models, with the UKMET model not far behind. Last year, the NOGAPS model did very poorly, forcing NHC to come up with some new consensus models this year, the TCOA and TVCA, that do not include the NOGAPS model. For those interested in learning more about the models, NOAA has a great training video (updated for 2011.)


Figure 5. Skill of computer model forecasts of Atlantic named storms 2010. OFCL=Official NHC forecast; GFS=Global Forecast System model; GFDL=Geophysical Fluid Dynamic Laboratory model; HWRF=Hurricane Weather Research Forecasting model; NOGAPS=Navy Operational Global Prediction System model; UKMET=United Kingdom Met Office model; ECMWF=European Center for Medium Range Weather Forecasting model; TVCN=one of the consensus models that lends together all (or most) of the above models. Image credit: National Hurricane Center 2010 verification report.

Next post
There will be 2 - 3 posts per day in my blog this week during Irene, with Angela Fritz and Rob Carver doing some of the afternoon and evening posts.

Jeff Masters

Hurricane

Updated: 03:22 PM GMT die 22o August, anno 2011

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Dangerous Tropical Storm Irene headed for the Dominican Republic

By: JeffMasters, 02:38 PM GMT die 21o August, anno 2011

Tropical Storm Irene roared into life last night, transitioning from a tropical wave to a 50 mph tropical storm in just a few short hours. Irene is getting organized quickly, and has the potential to become a hurricane by Monday morning. All interests in the Dominican Republic, Haiti, Cuba, the Bahamas, and South Florida should prepare for the arrival of this dangerous storm. An Air Force hurricane hunter aircraft in the storm found the strongest winds near 18°N latitude to the north of Irene's center at 8am this morning. After passing through the center, the plane returned to the area of strongest winds two hours later, and found that flight level winds at 5,000 feet had increased by about 5 - 8 mph. However, the pressure in the latest center fix taken at 10am EDT remained the same as two hours previously, 1007 mb, and the plane noted that Irene's center was not circular, signs that the storm still has some work to do before serious intensification can begin. Visible satellite loops and radar out of Martinique show the storm has rapidly organized this morning, with well-developed spiral bands forming and a large area of intense thunderstorms to the north of the center. Irene has shrugged off the dry air that was bothering it yesterday, and wind shear has fallen to the low range, 5 - 10 knots, as analyzed by the University of Wisconsin CIMSS group. Torrential rains and strong gusty winds are affecting the northern Lesser Antilles this morning. A wind gust of 41 mph was recorded at St. Eustatius at 8am local time.


Figure 1. Morning satellite image of Irene.

Track forecast for Irene
The computer models are in agreement that Irene will pass just south of Puerto Rico tonight, then hit the south coast of Hispaniola in the Dominican Republic or Haiti on Monday afternoon. Irene should then emerge into the channel between Haiti and Cuba on Tuesday afternoon, when the storm will have 12 or so hours over water before having to contend with Cuba. A trough of low pressure is expected to move across the Eastern U.S. on Wednesday and Thursday, turning Irene to the northwest and north by Thursday. The timing and strength of this trough varies considerably from model to model, and will be critical in determining where and when Irene will turn to the north. Irene's strength will also matter--a stronger Irene is more likely to turn northward earlier. The most likely path for Irene is a track just east of the Florida Peninsula and into Georgia, South Carolina, or North Carolina by next weekend, but a landfall near Miami then directly up the Florida Peninsula is also a reasonable solution--like Tropical Storm Fay of 2008 did. Fay formed just off the coast of Puerto Rico, and was never quite able to get organized enough to become a hurricane, due to passage over Hispaniola and Cuba. Fay topped out as a strong tropical storm with 70 mph winds, and did over $500 million in damage in the U.S., mostly due to flooding rains in Florida that accumulated to over 25 inches in a few areas. Fay also dumped heavy rains on Hispaniola, triggering flooding that claimed eight lives.


Figure 2. Track of Tropical Storm Fay of 2008.

Intensity forecast for Irene
Irene is embedded in a large envelope of moisture now, and wind shear will remain low, 5 - 10 knots, for the next five days. With water temperatures very warm, 28 - 30°C, these conditions should allow for intensification except when land is interfering. Irene's current appearance on satellite loops gives me the impression of a storm that is not fooling around, and I expect Irene will be a hurricane before hitting Hispaniola on Monday. Passage over Hispaniola will not destroy Irene, since it is a fairly large storm. Once the storm finishes with Hispaniola, it will have to deal with Cuba, which will keep Irene from intensifying significantly. Once Irene pops off the coast of Cuba Wednesday or Thursday into the Florida Straits, Irene will likely be a tropical storm. If the storm then has at least a day over water before hitting land, it will likely become a hurricane again, and could become a major hurricane if it ends up missing South Florida and moving over the warm waters on either side of the Florida Peninsula.

Harvey hits Belize
Tropical Storm Harvey made landfall at 2pm EDT on Saturday near Dangriga Town, Belize, as a tropical storm with 60 mph winds. Harvey continues to dump very heavy rains on southern Mexico, but dissipation is expected tonight as the storm pushes inland. Harvey was a small storm, and the strongest winds were confined to a short stretch of coast near where the center came ashore. Winds at Belize City, Belize on Saturday topped out at 15 mph.


Figure 3. Radar image of Harvey taken at 11:30am EDT on Saturday, August 20, 2011, a few hours before landfall in Belize. A small closed eye is visible just south of the offshore islands of Belize. Image credit: Belize National Meteorological Service.

Invest 98L northwest of the Cape Verde Islands
A tropical wave few hundred miles northwest of the Cape Verde Islands off the coast of Africa, Invest 98L, has become disorganized and lost most of its heavy thunderstorms. The disturbance is moving over colder waters and encountering drier air, and NHC is giving 98L only a 10% chance of developing into a tropical depression by Tuesday. The latest set of model runs keep 98L well out to sea away from any land areas over the next five days.

Links
Long-range radar out of Puerto Rico

Jeff Masters

Hurricane

Updated: 06:58 PM GMT die 09o January, anno 2012

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Irene roars into life; may become the season's first hurricane

By: JeffMasters, 12:03 AM GMT die 21o August, anno 2011

Tropical Storm Irene roared into life this evening, transitioning from a tropical wave to a 50 mph tropical storm in just a few short hours. An Air Force hurricane hunter aircraft in the storm was finishing up its mission when it suddenly came across a region with intense thunderstorms and surface winds of 50 mph. The aircraft found that a center of circulation had barely closed off on the southwest edge of this region, though the plane found almost no winds from the west around the circulation center. The 6:10pm EDT center fix found a central pressure of 1007mb, which is quite high for the observed 50 mph winds. Dry air to the north and west is slowing development, as well as moderate wind shear of 10 - 20 knots, as analyzed by the University of Wisconsin CIMSS group. Infrared satellite loops and radar out of Martinique show the storm is poorly organized, with no evidence of spiral bands. The center of Irene is expected to cross over the Caribbean island of Dominica early Sunday morning, but the heaviest thunderstorms lie to the north of the center, and will affect Guadeloupe, Antigua, and St. Kitts and Nevis.


Figure 1. Evening satellite image of Irene.

The computer models have shifted southwards since yesterday, and now take Irene south of Puerto Rico on Monday, and along the south shore of the Dominican Republic on Tuesday. On Wednesday, Irene should pass near or over southern Haiti, Eastern Cuba, and Jamaica. On Wednesday and Thursday, the models agree that a trough of low pressure will dip down over the Eastern U.S., which is likely to turn Irene to the north. The exact timing and strength of this trough varies considerably from model to model, and will be critical in determining where and when Irene will turn to the north. We can expect that Irene will impact Central Cuba, the Bahamas, and the Florida Keys on Thursday, but it is uncertain whether Irene's turn to the north will take the storm into the Gulf of Mexico or not. Irene most reminds me of Tropical Storm Fay of 2008. Fay formed just off the coast of Puerto Rico, and was never quite able to get organized enough to become a hurricane, due to passage over Hispaniola and Cuba. Fay topped out as a strong tropical storm with 70 mph winds, and did over $500 million in damage in the U.S., mostly due to flooding rains in Florida that accumulated to over 25 inches in a few areas. Fay also dumped heavy rains on Hispaniola, triggering flooding that claimed eight lives.


Figure 2. Track of Tropical Storm Fay of 2008.

Irene will be battling dry air and moderate wind shear of 10 - 20 knots through Sunday, and it will take the storm 1 - 3 days to build up an eyewall and intensify into a hurricane. Irene is more of a threat than Tropical Storm Emily of early August was, since Irene has closed off a center farther east than Emily did and has more time to organize before encountering Hispaniola. I don't think passage over Hispaniola will destroy Irene, since it is a fairly large storm, and is likely to be a hurricane by then. However, if Irene follows the NHC forecast, it will have an extended encounter with Hispaniola and Cuba on Tuesday through Wednesday that will probably weaken the storm below hurricane force. Keep in mind that the average error for an official 5-day forecast from NHC for a developed storm is 200 - 250 miles. Irene could easily miss Florida and move up the East Coast and hit North or South Carolina, or pass through the Florida Keys and into Gulf of Mexico, ending up who knows where. Given the uncertainties, this weekend would be a good time to go over your hurricane preparedness if you live anywhere in the Caribbean, Bahamas, or U.S. coast, since Irene could well be paying you a visit as a tropical storm or hurricane sometime in the next week.

Harvey hits Belize
Tropical Storm Harvey made landfall at 2pm EDT on Saturday near Dangriga Town, Belize, as a tropical storm with 60 mph winds. Harvey continues to dump very heavy rains on northern Guatemala, Belize, and portions of Mexico's Yucatan Peninsula as the storm tracks westwards at 12 mph. Dissipation is expected Sunday as the storm pushes inland. Harvey was a small storm, and the strongest winds were confined to a short stretch of coast near where the center came ashore. Winds at Belize City, Belize on Saturday topped out at 15 mph.


Figure 3. Radar image of Harvey taken at 11:30am EDT on Saturday, August 20, 2011, a few hours before landfall in Belize. A small closed eye is visible just south of the offshore islands of Belize. Image credit: Belize National Meteorological Service.

An exceptionally active early part of hurricane season
It's been a strangely hyperactive season for weak storms in the Atlantic so far this year. Tropical Storm Irene is the 9th named storm this year, and its formation date of August 20 ties 2011 with 1936 as the 2nd earliest date for formation of the season's 9th storm. Only 2005 had an earlier date. The first eight storms this year have stayed below hurricane strength, making 2011 the first hurricane season since record keeping began in 1851 to have more than six consecutive tropical storms that did not reach hurricane strength. As I discussed in Friday's post, a major reason for this is the lack of vertical instability over the tropical Atlantic so far this year. We've had a large amount of dry, sinking air over the tropical Atlantic, and the usual amount of dry, dusty air from the Sahara, both helping to keep the atmosphere stable and stop this year's storms from intensifying into hurricanes. Hurricane activity typically ramps up big-time by August 20, with more than 80% of all the hurricanes and 65% of all the tropical storms occurring after that date. At our current pace, 2011 will become the second busiest Atlantic hurricane season on record, with 24 - 27 named storms. There are only 21 names in the list of names for a hurricane season, so we may have to break out the Greek alphabet again in late October this year, as occurred in 2005. Ironically, this was the last time the current set of names was used in the Atlantic, so 16 of this year's 21 names are repeats of 2005. I'm not too happy about seeing another hurricane season challenge the Hurricane Season of 2005 in any way, and let's hope we don't retire another five names this year, like occurred in 2005! With vertical instability much lower this year than in 2005, and that year having already seen one storm (Dennis) retired by this point in the season, I doubt that will happen, though.


Figure 2. The annual cycle of average hurricane frequency in the Atlantic. Historically, about 35% of all the tropical storms and 15% of all the hurricanes will have occurred by August 20.

Invest 98L near the Cape Verde Islands
A tropical wave near Cape Verde Islands off the coast of Africa, Invest 98L, is spreading heavy rains and strong gusty winds to those islands today. So far this morning, top sustained winds measured in the Cape Verde Islands were 23 mph at Mindelo. 98L has a long stretch of ocean to cross before it could affect any land areas. Approximately 70 - 80% of all tropical cyclones that pass this close to the Cape Verde Islands end up curving out to sea and not affecting any other land areas, according to Dr. Bob Hart's excellent historical probability of landfall charts. The latest set of long-range model runs go along with this idea, and I'd be surprised if 98L threatens any land areas.

Jeff Masters

Hurricane

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Harvey drenching Belize; 97L a threat to the Caribbean and U.S.

By: JeffMasters, 04:16 PM GMT die 20o August, anno 2011

Tropical Storm Harvey is closing in towards a landfall this afternoon in Belize, and is dumping very heavy rains on northern Honduras, northern Guatemala, and Belize as it steadily moves west near 12 mph. A personal weather station on Roatan Island on the north coast of Honduras has received 6.68" of rain as of 10am EDT this morning from Harvey, and had a peak wind gust of 42 mph. The Roatan airport has received 3.55", and had a peak wind gust of 40 mph. The first significant spiral band from Harvey moved over Belize City at 7am local time, dropping nearly an inch of rain on the city. Belize National Meteorological Service radar shows that Harvey has appeared to close off an eyewall as of 11:30am EDT, which may allow the storm to intensify another 10 - 15 mph before landfall. The 11am NHC wind probability forecast gave Harvey a 3% chance of making it to hurricane strength, but the discussion noted that it wouldn't be that hard for Harvey to gain another 10 - 15 mph before landfall. I estimate there is a 30% chance that the winds along a 10-mile stretch of Belize coast where the eyewall makes landfall will reach hurricane force.


Figure 1. Radar image of Harvey taken at 11:30am EDT on Saturday, August 20, 2011, a few hours before landfall in Belize. A small closed eye is visible just south of the offshore islands of Belize. Image credit: Belize National Meteorological Service.


Figure 2. True-color MODIS image of Tropical Storm Harvey taken at 12:25pm EDT on Friday, August 19, 2011. An hour after this picture was taken, Harvey became a tropical storm with 40 mph winds. Image credit: NASA.

An exceptionally active early part of hurricane season
It's been a strangely hyperactive season for weak storms in the Atlantic so far this year. Tropical Storm Harvey is the 8th named storm this year, and its formation date of August 19 marks the 4th earliest date on record for the Atlantic's 8th storm. Only 2005, 1933, and 1936 had the 8th storm of the season form earlier. All eight storms this year have stayed below hurricane strength, making 2011 the first hurricane season since record keeping began in 1851 to have more than six consecutive tropical storms that did not reach hurricane strength. As I discussed in yesterday's post, a major reason for this is the lack of vertical instability over the tropical Atlantic so far this year. We've had a large amount of dry, sinking air over the tropical Atlantic, and the usual amount of dry, dusty air from the Sahara, both helping to keep the atmosphere stable and stop this year's storms from intensifying into hurricanes. Hurricane activity typically ramps up big-time by August 20, with more than 80% of all the hurricanes and 65% of all the tropical storms occurring after that date. With 97L looking like it will become a named storm in the next few days, at our current pace, 2011 will become the second busiest Atlantic hurricane season on record, with 24 - 27 named storms. There are only 21 names in the list of names for a hurricane season, so we may have to break out the Greek alphabet again in late October this year, as occurred in 2005. Ironically, we are using the 2005 list of names this year, so 16 of this year's 21 names are repeats of 2005. I'm not too happy about seeing a hurricane season challenge the Hurricane Season of 2005 in any way, and let's hope we don't retire another five names this year, like occurred in 2005! With vertical instability much lower this year than in 2005, and that year having already seen one storm (Dennis) retired by this point in the season, I doubt that will happen, though.


Figure 3. The annual cycle of average hurricane frequency in the Atlantic. Historically, about 35% of all the tropical storms and 15% of all the hurricanes will have occurred by August 20.

Invest 97L likely to become a tropical storm by Tuesday, could threaten the U.S.
A tropical wave near 14°N 56°W, about 450 miles east of the Lesser Antilles Islands, is moving west to west-northwest at 15 - 20 mph. This wave, designated Invest 97L, has built a respectable amount of heavy thunderstorm activity over the past day, but remains disorganized. Dry air to the north and west is slowing development, as well as moderate wind shear of 10 - 20 knots, as analyzed by the University of Wisconsin CIMSS group. An impressive amount of large-scale spin is obvious in visible satellite loops, but there is no sign of a well-defined surface circulation. An ASCAT pass at 9:04am EDT this morning showed a strong wind shift, but no closed circulation. Ocean temperatures are about 28.5°C, about 2°C above the threshold needed to support a tropical storm. A hurricane hunter aircraft will investigate 97L this afternoon.


Figure 4. Morning satellite image of the tropical disturbance Invest 97L.

The computer models have shifted southwards since yesterday, and now take 97L south of Puerto Rico on Monday, and along the south shore of the Dominican Republic on Tuesday. On Wednesday, 97L should pass near or over southern Haiti, Eastern Cuba, and Jamaica. On Wednesday and Thursday, the models agree that a trough of low pressure will dip down over the Eastern U.S., which is likely to turn 97L to the north. The exact timing and strength of this trough varies considerably from model to model, and will be critical in determining where and when 97L will turn to the north. We can expect that 97L will impact Central Cuba, the Bahamas, and the Florida Keys on Thursday, but it is uncertain whether 97L's turn to the north will take the storm into the Gulf of Mexico or not.

The computer models continue to enthusiastically develop 97L, and all the ingredients seem to be in place for a tropical storm to form by Monday or Tuesday as 97L crosses the Northeast Caribbean. The atmosphere is expected to be moister over the Caribbean, wind shear will remain a low 5 - 10 knots, and sea surface temperatures will increase to near 29°C. The main impediment for development will likely be two-fold: too much dry, stable air, and proximity to land.

There has been an unusual amount of dry, stable air in the Atlantic this year, due to a combination of dry air from Africa, and upper-atmosphere dynamics creating large areas of sinking air that dry as they warm and approach the surface. This stable air has been largely responsible for the fact that none of our seven tropical storms so far this year has made it to hurricane strength, despite the presence of sea surface temperatures that are the 3rd warmest on record across the tropical Atlantic. Tropical Storm Emily in early August encountered problems with dry air when it crossed the Northeast Caribbean, and 97L may have similar difficulties. There will be some moderate wind shear of 10 - 20 knots to the north of 97L over the next week, and this shear may work in concert with the dry air to slow development.

Given 97L's current disorganization and problems with dry air, I believe it is unlikely the storm will be stronger than a 55 mph tropical storm on Tuesday morning, when it will be close enough to the mountainous island of Hispaniola that a good portion of its circulation will be over the island, disrupting the storm. 97L may also make a direct hit on the Dominican Republic or Haiti sometime Tuesday or Wednesday morning, which could even destroy the storm, like happened to Tropical Storm Emily in early August. However, there is at least a 30% chance that 97L will miss Hispaniola, and slide through the waters between Jamaica and Eastern Cuba, allowing the storm to intensify into a hurricane south of Cuba. At this point, it appears there are too many hurdles for 97L to negotiate for it to arrive in the Florida Straits as a hurricane, since the storm has to cross Cuba and/or Hispaniola, plus contend with dry air and wind shear. However, 97L hasn't even developed a well-defined circulation yet, making it difficult for the models to zero in on a solution for where the storm might go. The average error for an official 5-day forecast from NHC for a developed storm is 200 - 250 miles; the error will be much higher for a 6 to 7-day forecast of an Invest that hasn't developed yet. Given the uncertainties, this weekend would be a good time to go over your hurricane preparedness if you live anywhere in the Caribbean, Bahamas, or Florida, since 97L could well be paying you a visit as a tropical storm or hurricane sometime in the next week.


Figure 5. Skill of computer model forecasts of Atlantic named storms during 2010. OFCL=Official NHC forecast; GFS=Global Forecast System model; GFDL=Geophysical Fluid Dynamic Laboratory model; HWRF=Hurricane Weather Research Forecasting model; NOGAPS=Navy Operational Global Prediction System model; UKMET=United Kingdom Met Office model; ECMWF=European Center for Medium Range Weather Forecasting model; TVCN=one of the consensus models that lends together all (or most) of the above models. Image credit: National Hurricane Center 2010 verification report.

Which model should you trust?
Wunderground provides a web page with computer model forecasts for many of the best-performing models used to predict hurricane tracks. So which is the best? Well, the best forecasts are made by combining the forecasts from three or more models into a "consensus" forecast. Over the past decade, NHC has greatly improved their forecasts by relying on consensus forecast models made using various combinations of the GFS, GFDL, NOGAPS, UKMET, HWRF, and ECMWF models. If you average together the track forecasts from these models, the NHC official forecast will rarely depart much from it, and the NHC forecast has been hard to beat over the past few years. The single best-performing model over the past two years has been the ECMWF (European Center model). This model out-performed the official NHC forecast in 2010 for 1-day, 2-day, 3-day and 4-day forecasts, and in 2009 for 4-day and 5-day forecasts. You can view ECMWF forecasts on our wundermap with the model layer turned on. The European Center does not permit public display of tropical storm positions from their hurricane tracking module of their model, so we are unable to put ECMWF forecasts on our computer model forecast page that plots positions from the other major models. As seen in Figure 5, over the past two years, the GFS and GFDL model have been the next best models, with the UKMET model not far behind. Last year, the NOGAPS model did very poorly, forcing NHC to come up with some new consensus models this year, the TCOA and TVCA, that do not include the NOGAPS model. For those interested in learning more about the models, NOAA has a great training video (updated for 2011.)

Invest 98L near the Cape Verde Islands
A tropical wave near Cape Verde Islands off the coast of Africa, Invest 98L, is spreading heavy rains and strong gusty winds to those islands today. So far this morning, top sustained winds measured in the Cape Verde Islands were 23 mph at Mindelo. Water temperatures are warm, near 27 - 28°C, and wind shear is low, 5 - 10 knots, so 98L should continue to organize today before running into more hostile conditions on Sunday. NHC gave the storm a 40% chance of developing into a tropical depression by Monday morning in their 8am advisory. Once 98L passes to the east of the Lesser Antilles, it has a long stretch of ocean to cross before it could affect any other land areas. Approximately 70 - 80% of all tropical cyclones that pass this close to the Cape Verde Islands end up curving out to sea and not affecting any other land areas, according to Dr. Bob Hart's excellent historical probability of landfall charts. The latest set of long-range model runs go along with this idea, and I'd be surprised if 98L threatens any land areas.

Dismal Swamp fire creating dangerous air pollution in Virginia
Lightning from a thunderstorm on August 4 sparked a fire in Southeast Virginia's Dismal Swamp, which continues to burn out of control. Yesterday, air quality alerts for Code Purple pollution--the worst category of air pollution--were posted for Suffolk, Virginia and continue today. The region, including the cities of Norfolk and Hampton Roads, have seen an increase in hospital admissions for people with breathing problems, plus an increase in traffic accidents due to low visibility conditions on area roads. The fire has burned 6100 acres and is 15% contained. Given that it is burning more than 1 foot underground, it will be difficult to put out unless heavy rains raise the water table. The region is under "Abnormally dry" drought conditions, the lowest category of drought on the five-category drought scale.

Jeff Masters

Hurricane

Updated: 05:16 PM GMT die 20o August, anno 2011

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TD 8 forms; 97L a potential threat to the Caribbean and U.S.

By: JeffMasters, 03:30 PM GMT die 19o August, anno 2011

Tropical Depression Eight formed last night near the coast of Honduras, and is headed westwards towards a landfall in Belize on Saturday. TD 8 is a small storm, so will impact a relatively small area of northern Honduras, northern Guatemala, all of Belize, and southern portions of Mexico's Yucatan Peninsula. TD 8 has just enough room between its center and the coast of Honduras to intensify into a moderate strength tropical storm with 50 - 60 mph winds before landfall. It is very unlikely TD8 has the time or room to intensify into a hurricane; NHC gave the storm just a 7% chance of making it to hurricane strength in their 11am EDT wind probability forecast. Should TD8 make it to tropical storm strength, it would be called Harvey.


Figure 1. Morning satellite image of TD 8.

Invest 97L likely to become a tropical storm next week, could threaten the U.S.
A tropical wave near 14°N 48°W, about 800 miles east of the Lesser Antilles Islands, is moving westward near 20 mph. This wave, designated Invest 97L by NHC yesterday, has seen a marked increase in its heavy thunderstorm activity this morning, but dry air to the north and west is slowing development. An impressive amount of large-scale spin is obvious in visible satellite loops, but the storm is at least a day away from forming a well-defined surface circulation. Ocean temperatures are about 28.5°C, about 2°C above the threshold needed to support a tropical storm, and wind shear is low, 5 - 10 knots.


Figure 2. Morning satellite image of the tropical wave 97L.

The computer models have shown an unusual amount of agreement in developing 97L over the past few days, and all the ingredients seem to be in place for a tropical storm to form by Monday or Tuesday as 97L crosses the Northeast Caribbean. The atmosphere is expected to be moister over the Caribbean, wind shear will remain a low 5 - 10 knots, and sea surface temperatures will increase to near 29°C. The main impediment for development will likely be two-fold: too much dry, stable air, and proximity to land.

As seen in Figure 3, there has been an unusual amount of dry, stable air in the Atlantic this year, due to a combination of dry air from Africa, and upper-atmosphere dynamics creating large areas of sinking air that dry as they warm and approach the surface. This stable air has been largely responsible for the fact that none of our seven tropical storms so far this year has made it to hurricane strength, despite the presence of sea surface temperatures that are the 3rd warmest on record across the tropical Atlantic. Tropical Storm Emily in early August encountered problems with dry air when it crossed the Northeast Caribbean, and 97L may have similar difficulties.


Figure 3. Vertical instability of the atmosphere during 2011 in the Caribbean (left) and tropical Atlantic between the Lesser Antilles Islands and coast of Africa (right.) The instability is plotted in °C, as a difference in temperature from near the surface to the upper atmosphere. Thunderstorms grow much more readily when vertical instability is high. Observed vertical instability (blue line) has been much lower than the climatological average from previous years (black line), due to an unusual amount of dry air in the atmosphere, inhibiting tropical storm development this year. Image credit: NOAA/CIRA.

Encounters with land will be another potential major problem for 97L. Most of the computer models take 97L near or over Puerto Rico Sunday night, then very close to or over mountainous Hispaniola Monday night through Tuesday. It is unlikely that 97L will be stronger than a 55 mph tropical storm when it encounters these islands, and passage over the islands could severely disrupt the storm. However, if 97L takes a path just south or north of Hispaniola, the potential exists for the storm to intensify into a hurricane.

There will be moderate wind shear of 10 - 20 knots to the north of the islands early next week, so a path just to the south of the Dominican Republic and Haiti would be more likely to let 97L intensify into a hurricane. A west-northwest motion is likely for 97L through Wednesday, which would bring the storm to the vicinity of Jamaica-Central Cuba-the Central Bahamas on Wednesday. On Wednesday and Thursday, the models agree that a trough of low pressure will dip down over the Eastern U.S., which is likely to turn 97L to the north. The exact timing and strength of this trough varies considerably from model to model, and will be critical in determining where and when 97L will turn to the north. The best model for predicting the timing and strength of such troughs over the past two years has been the ECMWF (European Center model), and this model currently brings 97L into the Florida Keys on Thursday night next week. You can view ECMWF forecasts on our wundermap with the model layer turned on. The European Center does not permit public display of tropical storm positions from their hurricane tracking module of their model, so we are unable to put ECMWF forecasts on our computer model forecast page that plots positions from the other major models.

Remember that a 7-day forecast by even our best model will be off by an average of over 700 miles, so it is too early to tell what part of the U.S. might be most at risk from a strike by 97L. This weekend would be a good time to go over your hurricane preparedness.


Figure 4. Morning satellite image of Invest 98L off the coast of Africa.

Invest 98L near the coast of Africa
A tropical wave near the coast of Africa, a few hundred miles southeast of the Cape Verde Islands, is moving west to west-northwestward at 10 - 15 mph. This wave, designated Invest 98L by NHC yesterday, is large and well-organized, with a modest amount of spin and heavy thunderstorm activity. 98L will bring strong, gusty winds and heavy rains to the Cape Verde Islands today and Saturday as the storm skirts to the south. So far this morning, top sustained winds measured in the islands were 24 mph at Mindelo. Water temperatures are warm, near 27 - 28°C, and wind shear is low, 5 - 10 knots, so 98L should continue to organize today. NHC gave the storm a 50% chance of developing into a tropical depression in their 8am advisory. Once 98L passes to the west of the Cape Verde Islands, it has a long stretch of ocean to cross before it could affect any other land areas. Approximately 70 - 80% of all tropical cyclones that pass this close to the Cape Verde Islands end up curving out to sea and not affecting any other land areas, according to Dr. Bob Hart's excellent historical probability of landfall charts. The latest set of long-range model runs go along with this idea, but it is too early to be confident of this.

Jeff Masters

Hurricane

Updated: 03:37 PM GMT die 19o August, anno 2011

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Caribbean disturbance 93L to drench Honduras; 97L disturbance worth watching

By: JeffMasters, 03:04 PM GMT die 18o August, anno 2011

A westward-moving tropical wave in the Central Caribbean a few hundred miles south-southwest of Jamaica, Invest 93L, has continued to increase in organization, and is close to tropical depression status. 93L is a small system, but has built up a respectable area of heavy thunderstorms around its center. A few low-level spiral bands are apparent on satellite imagery, but there is almost no upper-level outflow apparent, and a surface circulation is not obvious. 93L has moistened its environment somewhat over the past day, but dry air is still in evidence around the storm, particularly to the southeast, as seen on water vapor satellite images. Wind shear continues to be low, 5 - 10 knots. There is a hurricane hunter mission scheduled for this afternoon at 2pm EDT to see if a tropical depression is forming.


Figure 1. Morning satellite image of 93L.

Heavy rains from 93L will begin spreading over Northern Honduras and Northeast Nicaragua tonight. The forward motion of 93L will slow to 5 - 10 mph by Friday, so the storm could be a major rain event for Northern Honduras, with rain amounts of 4 - 8 inches likely by the time the storm reaches Belize on Saturday. Heavy rains will spread to Belize and Mexico's Yucatan Peninsula by Friday night or Saturday morning. The latest SHIPS model forecast shows wind shear remaining in the low range and the atmosphere steadily moistening over the next two days, which should allow 93L to reach tropical storm strength. All of the models agree that the ridge of high pressure steering 93L to the west will remain strong, forcing the storm into a landfall Friday in Northeast Honduras, or Saturday near the Belize/Mexico border. It is possible that 93L will have time to intensify into a Category 1 hurricane before then, though landfall as a tropical storm would be more likely, given the dry air that 93L needs to overcome, and the possibility that the storm will pass too close to the northern coast of Honduras. Regardless, heavy rain will be a major threat from 93L. NHC gave 93L an 80% chance of developing into a tropical depression by Saturday morning in their 8am outlook. If 93L does cross the Yucatan Peninsula and enters the Gulf of Mexico, a strong ridge of high pressure should keep the storm moving due west to make a second landfall along the Mexican coast, well south of Texas.


Figure 2. Morning satellite image of the tropical wave 97L midway between the Lesser Antilles and the coast of Africa.

Invest 97L midway between the Lesser Antilles and the coast of Africa
A tropical wave near 14°N 40°W, midway between the Lesser Antilles Islands and the coast of Africa, is moving westward near 15 - 20 mph. This wave, designated 97L by NHC this morning, has little heavy thunderstorm activity associated with it due to dry air, but an impressive amount of large-scale spin is obvious in visible satellite loops. 97L is expected to arrive in the Lesser Antilles Islands by Saturday. Over the past day, all four of our reliable models for predicting tropical storm genesis have predicted that this wave could develop into a tropical depression sometime Saturday through Monday, so 97L needs to be watched carefully. NHC gave 97L a 10% chance of developing into a tropical depression by Saturday morning in their 8am outlook, and it is unlikely that this storm will pose much of a threat to the Lesser Antilles. It will take several days for the storm to overcome the large amount of dry air surrounding it, even though wind shear is a low 5 - 10 knots. By Saturday, the wave will find a moister atmosphere and warmer sea surface temperatures near the northern Lesser Antilles, and more rapid development may occur. However, there is expected to be high wind shear associated with an upper level low pressure system to the north of Puerto Rico at that time, and this wind shear may interfere with development. 97L is expected to take a west-northwest track through the Northeast Caribbean bringing the storm near Puerto Rico by Sunday or Monday. Long-range model runs, which are highly unreliable, foresee that 97L could be a threat to Hispaniola, Eastern Cuba, the Bahamas, and Florida by the middle to end of next week.

Jeff Masters

Hurricane

Updated: 03:07 PM GMT die 18o August, anno 2011

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Texas heat wave smashes more records; 93L more organized

By: JeffMasters, 03:26 PM GMT die 17o August, anno 2011

Texas' Texas-sized drought and heat wave is setting new records, as August temperatures regularly topping 100° continue to impact most of the state. The high temperature hit 102° at the Houston Intercontinental Airport yesterday, a record for the date, and the 16th consecutive day of 100°+ heat. The 16-day streak is a new record. The previous record was 14 straight days, ending on July 19, 1980.

The low temperature yesterday morning at Dallas/Fort Worth International was 86°--the all-time highest minimum temperature recorded there. This is the 4th time this summer Dallas has had an 86° minimum temperature, with the other dates being July 26, August 3, and August 4. Prior to this year, the hottest minimum temperature ever recorded in Dallas was 85° on September 1, 1939 (which they also matched this summer on July 25, August 7, and again this morning.) Thus Dallas has matched or exceeded their all-time hottest minimum temperature from previous years seven times this year. It's extremely rare for a station with a long observation history spanning more than fifty years to break an all-time record seven times in one year; if anyone can find an example of this in the past, I'd love to hear about it. The National Climatic Data Center records page is a good place to look. Dallas has had 40 days with a minimum temperature of 80° or higher this year, breaking the previous record of 39 days, set in 1998. Dallas had a streak of 40 straight days with a maximum temperature above 100° which ended August 10, good for 2nd place all-time, next to a 42-day streak in 1980.


Figure 1. The amount of rain needed to break the Texas drought is in excess of 15 inches (purple colors) over most of the state. This year's drought is officially Texas' worst one-year drought on record. Image credit: NOAA/NWS.

According to the National Climatic Data Center, twelve other major airports set or tied their all-time high minimum temperature two or more times this summer: San Angelo, TX (four times); Lake Charles, LA (three times); Bristol, TN; Indianapolis, IN; Trenton, NJ; Newark, NJ; West Palm Beach, FL; Shreveport, LA; Beckley, WV; Texarkana, AR; Lake Charles, LA; Lubbock, TX; plus, Fort Worth Meacham Field. This year's total of fourteen airports that broke their all-time high minimum temperature multiple times this summer is similar to last year's total of ten sites. Most notable last year was West Palm Beach, Florida, which tied it's all-time high minimum temperature of 83° five times in 2010.

Fifteen major airports have tied or broken their all-time highest temperature multiple times this summer: Tyler, TX (three times); Tallahassee, FL (three times); Fort Smith, AR; Harrison, AR; Tulsa, OK; McAlester, OK; Longview, TX; and Oklahoma City, OK, Ypsilanti, MI; Altoona, PA; Dubois, PA; Salisbury, MD; Raton, NM; Amarillo, TX; and Dalhart, TX. For comparison, only three stations broke their all-time maximum temperature record multiple times in 2010: Wilmington, DE; Norfolk, VA; and Richmond, VA.


Figure 2. Morning satellite image of Invest 93L.

Caribbean disturbance 93L
A westward-moving tropical wave in the Central Caribbean a few hundred miles south of Hispaniola, Invest 93L, has increased in organization overnight, building up a modest amount of heavy thunderstorms. Low-level spiral bands have begun to form on all sides of the storm this morning. There are currently no signs of a surface circulation, though there is plenty of large-scale rotation apparent on satellite imagery. Dry air surrounds 93L and has infiltrated the center of the disturbance, giving 93L a doughnut-like appearance. However, the disturbance is steadily moistening its environment and is under low wind shear of 5 - 10 knots, so this dry air should gradually mix out today and allow 93L to continue to organize. There is a hurricane hunter mission scheduled for this afternoon at 2pm EDT to see if a tropical depression is forming.

93L will bring heavy rain showers to southern Haiti this afternoon and to Jamaica tonight. By Thursday, 93L's forward motion will slow to 10 - 15 mph, and the storm will bring heavy rains to Northern Honduras and Northeast Nicaragua. These rains will spread to Belize and Mexico's Yucatan Peninsula by Saturday. The latest SHIPS model forecast shows wind shear remaining in the low range and the atmosphere steadily moistening as 93L enters the Western Caribbean on Thursday. All of the models agree that the ridge of high pressure steering 93L to the west will remain strong, forcing the storm into a landfall Friday in Northeast Nicaragua or Northeast Honduras. It is possible that 93L will have time to intensify into a Category 1 hurricane before then, though landfall as a tropical storm would be more likely, given the dry air that 93L needs to overcome. Regardless of development, the storm will bring very heavy rains of 4 - 8 inches or more to Nicaragua and Honduras. These rains are likely to cause dangerous flash flooding and mudslides. NHC gave 93L a 30% chance of developing into a tropical depression by Friday morning in their 8am outlook; I'd put these odds at 50% now, given the continued increase in organization seen on satellite images.


Figure 3. Morning satellite image of the tropical wave 500 miles west-southwest of the Cape Verde Islands.

Elsewhere in the tropics
A tropical wave near 14°N 34°W, about 500 miles west-southwest of the Cape Verde Islands off the coast of Africa, is moving westward near 15 - 20 mph. This wave has little heavy thunderstorm activity associated with it due to dry air, but an impressive amount of large-scale spin is obvious in visible satellite loops. This wave is expected to arrive in the Lesser Antilles Islands by Saturday. Three of our four reliable models for predicting tropical storm genesis predict that this wave could develop into a tropical depression sometime Friday through Sunday. A west-northwest track through the Northeast Caribbean bringing the storm near Puerto Rico by Sunday or Monday is favored by most of the models.

Jeff Masters

Drought Heat Hurricane

Updated: 08:01 PM GMT die 17o August, anno 2011

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Globe's 7th warmest July; remarkable heat in Asia; little change to 93L

By: JeffMasters, 02:34 PM GMT die 16o August, anno 2011

July 2011 was the globe's 7th warmest July on record, according to the National Oceanic and Atmospheric Administration (NOAA) National Climatic Data Center (NCDC). NASA's Goddard Institute for Space Studies rated July the 3rd warmest on record. July 2011 global land temperatures were the 5th warmest on record, and ocean temperatures were the 11th warmest on record. Global satellite-measured temperatures for the lowest 8 km of the atmosphere were the 6th or 3rd warmest in the 34-year record, according to Remote Sensing Systems and the University of Alabama Huntsville (UAH). Arctic sea ice in July was the lowest on record, going back to 1979.


Figure 1. Departure of temperature from average for July 2011. Image credit: National Climatic Data Center (NCDC).

Remarkable heat in Asia
For the second consecutive summer, some of the hottest temperatures in Earth's recorded history have scorched Asia. The six hottest (undisputed) temperatures ever measured in Asia have all occurred in during the past two summers:

1) 53.5°C (128.3°F) at Moenjodaro, Pakistan on May 26, 2010
2) 53.3°C (127.9°F) at Mitrabah, Kuwait on August 3, 2011
3) 53.1°C (127.6°F) at Sulaibiya, Kuwait on June 15, 2010
4) 53.0°C (127.4°F) at Tallil, Iraq on August 3, 2011
4) 53.0°C (127.4°F) at Dehloran, Iran on July 28, 2011
4) 53.0°C (127.4°F) at Sibi, Pakistan, on May 26, 2010


Asia's official all-time hottest temperature is 54°C measured at Tirat Zvi, Israel on June 21, 1942. However, as explained by our weather historian, Christopher C. Burt, this record is under serious dispute. Weather records researchers Howard Rainford and Maximiliano Herrera discovered that the thermograph trace of the record had been mis-read as one degree higher than it actually was, and there were other irregularities with the data. Also, a temperature in excess of 54°C was measured in Mitribah, Kuwait in July 2010, but the temperature sensor was found to be faulty.

Last year, twenty nations set all-time heat records. So far this year, there have been six such records set:

Kuwait recorded its hottest temperature on record on August 3, 2011, when the mercury hit 53.3°C (127.0°F) at Mitrabah. The previous record was 53.1°C in Sulaibiya on June 15, 2010. According to weather records researcher Maximiliano Herrera, who has been corresponding with representatives from the Kuwait Meteorological Center, the reading has been confirmed as authentic. The 53.3°C (127.0°F) at Mitrabah thus represents:

1) New official national record for Kuwait
2) Second highest (undisputed) temperature ever recorded in Asia
3) Highest temperature ever recorded in an Arabic country
4) Third hottest location in the planet together with Lake Havasu City, AZ (after Death Valley, CA and Moenjodaro, Pakistan)
5) A new world record for August

Iraq recorded its hottest temperature on record on August 3, 2011 in Tallil (Ali military airbase), when the mercury hit 53°C (127.4°F). The previous record was 52.3°C recorded at Diwanya FOB airbase a few days before.

Armenia recorded its hottest temperature on record on July 31 in Meghri, when the mercury hit 43.7°C (110.7°F). The previous record was 43.1°C in Meghri on July 17, 2005.

Iran recorded its hottest temperature in its history on July 28, 2011, when the mercury hit 53°C (127.4°F) at Dehloran. The previous previous record was set just one day earlier at Omidieh and Shoshtar, when the mercury hit 52.6°C (126.6°F).

Republic of the Congo set a new all-time extreme heat record on March 8, 2011, when the temperature hit 39.2°C (102.6°F) at M'Pouya. Congo's previous all-time hottest temperature was 39.0°C (102.2°F) at Impfondo on May 14, 2005.

Special mention:
Russia had its hottest temperature on record at a regular synoptic reporting station on July 30, 2011, when the mercury hit 44.3°C (111.7°F) at Divnoe in Russia's Kalmykia Republic. Three hotter temperatures have been recorded at automated stations: 45.4°C in 2010 at a hydrological station at Utta, plus readings of 45°C at El'ton and 44.5°C at Verhjnky Baskunkak in August 1940.

No nations have set an all-time coldest temperature record this year, or did so in 2010.

Weather records researcher Maximiliano Herrera is the primary source of the weather records listed here; he maintains a comprehensive list of extreme temperature records for every nation in the world on his website.

Gert misses Bermuda
Tropical Storm Gert brushed by Bermuda yesterday, bringing one brief rain shower and top winds of just 21 mph to the Bermuda Airport. Gert is headed northeastwards out to sea over colder waters, and does not have long to live. Gert is the 7th consecutive named storm in the Atlantic that has not reached hurricane strength. This is the first time that has occurred since record keeping began in 1851. However, it is quite possible such an event occurred before we had satellites to identify weak tropical storms that stayed out to sea. The previous record was six consecutive tropical storms without a hurricane, set most recently in 2002. While ocean temperatures in the tropical Atlantic have been very warm, ranking as the 3rd warmest on record during July, the atmosphere has been more stable and drier than usual, making it difficult for this year's storms to attain hurricane strength.


Figure 2. True color MODIS image taken from NASA's Aqua satellite of Tropical Storm Gert at 17:40 UTC on Monday, August 14, 2011. At the time, Gert was near peak strength, as a 60 mph tropical storm. Image credit: NASA.

Caribbean disturbance 93L
A large but disorganized tropical wave, (Invest 93L), is moving westwards at 15 - 20 mph over the eastern Caribbean Sea, a few hundred miles south of Puerto Rico. This wave has a modest amount of heavy thunderstorms and no signs of a surface circulation, though there is some large scale rotation apparent on satellite imagery. Dry air surrounds 93L, and is interfering with development. However, the disturbance is steadily moistening its environment and is under low wind shear of 5 - 10 knots, so it could begin to organize at any time. There is a hurricane hunter mission scheduled for this afternoon into 93L, but this mission will probably be cancelled given 93L's current lack of development.

93L will bring heavy rain showers to southern Haiti on Wednesday, and to Jamaica on Wednesday night. By Thursday, 93L's forward motion will slow to 10 - 15 mph, bringing heavy rains to Northern Honduras on Thursday and Friday, and Belize and Mexico's Yucatan Peninsula by Saturday. Some development of 93L is is likely beginning on Wednesday and Thursday in the Western Caribbean, as the latest SHIPS model forecast shows wind shear remaining in the low range and the atmosphere steadily moistening as 93L enters the Western Caribbean. However, a path too far south near the coast of Honduras may interfere with development, as predicted by the NOGAPS and GFS models, which dissipate 93L over northern Honduras. The best chances for development will probably occur early next week if 93L crosses the Yucatan Peninsula and enters the Gulf of Mexico, assuming the system survives the crossing intact and is not too far south, as predicted by the ECMWF and UKMET models. These models are currently predicting that the steering pattern early next week over the Gulf of Mexico will be similar to what we saw with Tropical Storm Arlene earlier this year, favoring a track towards Northeast Mexico. The HWRF model is predicting a more northerly track for 93L across Jamaica and the western tip of Cuba into the Gulf of Mexico, but this model develops 93L too quickly, unrealistically making it a hurricane by Thursday. The HWRF model thus predicts a deeper storm that would be steered farther to the north due to upper level winds with less of a straight east-to-west motion than a much weaker (and more realistic) 93L would go. Although it is risky to predict what might happen more than five days in advance, the odds of 93L making a U.S. landfall currently appear low, 20% or less. NHC gave 93L a 20% chance of development by Thursday morning in their 8am EDT Tropical Weather Outlook. These odds should probably be bumped up to 30% later today.


Figure 3. Morning satellite image of Invest 93L, taken at 7:45am EDT August 16, 2011. Image credit: NASA/GSFC.

Elsewhere in the tropics
A tropical wave a few hundred miles southwest of the Cape Verde Islands off the coast of Africa is moving westward near 15 - 20 mph, and is expected to arrive in the Lesser Antilles Islands by Saturday. Both the GFS and UKMET models develop this wave into a tropical depression by Friday or Saturday.

Jeff Masters

Climate Summaries Heat Hurricane

Updated: 05:58 PM GMT die 18o August, anno 2011

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Gert brushing Bermuda; a new all-time 1-day rainfall record for NYC

By: JeffMasters, 02:30 PM GMT die 15o August, anno 2011

Tropical Storm Gert, the 7th named storm of the Atlantic hurricane season, is here. Gert's formation on August 14 marks the 4th earliest date for the season's 7th storm. Only 2005, 1995, and 1936 have had an earlier formation of the season's 7th storm. Gert will pass very close to Bermuda today, but thus far the island has had no wind or rain from Gert, with top winds at the Bermuda Airport of just 9 mph as of 10 am EDT. Radar out of Bermuda shows the rains from Gert are staying just offshore, moving northward, parallel to the island. An Air Force hurricane hunter aircraft is in the storm, and has found that Gert has not changed much in intensity since last night. Top surface winds seen by their SFMR instrument this morning as of 10am EDT were 48 mph, though higher winds of 58 mph that may be erroneous due to rain interference were measured. It currently appears that Gert's northerly motion will keep virtually all of the storm's rains just offshore from from Bermuda. Gert should not trouble any land areas after moving past Bermuda.


Figure 1. Morning radar image of Gert from the Bermuda radar .

Elsewhere in the tropics
The disturbance we've been tracking over the past few days in the open Atlantic between Africa and the Lesser Antilles, Invest 93L, has regenerated a modest amount of heavy thunderstorms and will bring heavy rain showers and gusty winds to the Lesser Antilles today and Tuesday as it moves westwards through the islands at 15 - 20 mph. Dry air surrounds 93L, and is interfering with development. However, the disturbance is steadily moistening its environment and is under low wind shear of 5 - 10 knots, so could begin to organize over the next few days as it tracks across the Caribbean. The latest 06Z run of the NOGAPS model is showing weak development of 93L once it reaches the western Caribbean, with a track over Mexico's Yucatan Peninsula and into the Gulf of Mexico by this weekend. Stay tuned.


Figure 2. Radar-estimated rainfall for the past 2 days from the Long Island, NY radar.

New York City sets an all-time 1-day rainfall record
A long series of "training" thunderstorms that each moved along the same path deluged the New York City and Newark areas yesterday, smashing an all-time 1-day rainfall record at New York City's JFK Airport, which recorded 7.80 inches of rain. It was the most rain at JFK since record keeping began in 1948. The previous record was a 6.3" deluge on June 30, 1984. New York City's official measuring site, Central Park, got 5.81" yesterday, the fifth wettest day on record there. The 6.40" that fell on Newark, NJ yesterday was that city's 2nd heaviest 1-day rainfall in history, next to the 6.73" that fell on November 3, 1977.

Jeff Masters

Hurricane

Updated: 04:24 PM GMT die 15o August, anno 2011

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Tropical Depression Seven forms

By: JeffMasters, 02:25 PM GMT die 14o August, anno 2011

The latest in our unusual number of weak tropical cyclones this season, Tropical Depression Seven, has formed to the southeast of Bermuda. Unless you live in Bermuda, TD 7 is not going to be a concern. Radar out of Bermuda shows an area of rain on the northern side of TD 7 beginning to approach the island, and rain from the storm will likely affect the island tonight and on Monday. TD 7 is not well-organized, and has only limited heavy thunderstorms, as seen on visible satellite images. While wind shear is a low 5 - 10 knots, dry air surrounds TD 7, and is keeping the storm from intensifying. None of the computer models foresee that TD 7 will ever become more than a weak tropical storm.


Figure 1. Morning satellite image of TD 7.

92L
TD 7 isn't the only system Bermuda needs to watch, Invest 92L is a day behind it, and will follow a path very similar to TD 7's. The disturbance will pass close to Bermuda on Tuesday, bringing the island a second round of tropical rains. However, Invest 92L is very disorganized, as seen on recent visible satellite loops. Dry air and close proximity to TD 7 will likely keep 92L from showing significant development over the next two days, with NHC giving the system just a 30% chance of developing into a tropical depression by Tuesday morning.

Elsewhere in the tropics
The disturbance midway between the Lesser Antilles Islands and the coast of Africa we've been tracking over the past few days, Invest 93L, has fallen apart and is no longer a threat to develop. This system will need to be watched once it enters the Caribbean later this week, though. None of the reliable models for predicting tropical cyclone formation predict development of this system or any new disturbances over the coming week.

Jeff Masters

Hurricane

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Tropical Storm Franklin forms

By: JeffMasters, 04:41 PM GMT die 13o August, anno 2011

Tropical Storm Franklin, the sixth named storm of the 2011 Atlantic hurricane season, formed this morning in the open Atlantic north of Bermuda. The usual date of formation for the 6th storm of the year is September 8, so we are well ahead of climatology. However, the usual date for the first hurricane of the season is August 10, and we still have not had a hurricane yet this year. All six of this year's storms have been tropical storms, making 2011 the first season since 2002 when that has occurred. Franklin is headed eastwards out sea, away from any land areas, and does not have long to live.


Figure 1. Noon satellite photo of Invest 94L, showing the well-defined swirl of its low-level circulation.

94L
A low pressure system near 27°N 60°W, about 450 miles southeast of Bermuda, has developed a well-defined surface circulation, as seen on visible satellite images. However, this system, Invest 94L, has almost no heavy thunderstorm activity, due to dry air to its west being injected into its core by moderate wind shear of about 10 knots. The latest SHIPS model forecast is showing shear remaining in the moderate range and the atmosphere moistening in the vicinity of 94L over the next three days, which may allow the system to build enough heavy thunderstorms to become a tropical depression. None of the reliable models for predicting tropical storm formation (GFS, ECMWF, NOGAPS, and UKMET) show development of 94L, and NHC gave 94L a 30% chance of developing into a tropical depression by Monday morning in their 8am outlook. I'd put these odds higher, at 50%, given 94L's well-defined surface circulation. Bermuda is the only land area that needs to be concerned with 94L, with the storm making its closest pass on Monday. 94L should then curve north and northeastwards out to sea.

92L
An African wave near 20°N 54°W, about 600 miles east-northeast of the northern Lesser Antilles Islands, is moving west-northwest at 20 mph. This system, Invest 92L, has only modest amount of heavy thunderstorm and is very disorganized, as seen on recent visible satellite loops. An ASCAT pass from 9:49 am EDT this morning showed no surface circulation and only a slight wind shift associated with 92L. Water vapor satellite loops show that a large area of dry air surrounds 92L, and this dry air is causing problems for the storm. The SHIPS model and University of Wisconsin CIMSS wind shear analysis are showing moderate wind shear near 10 knots affecting 92L.

Forecast for 92L
Light to moderate wind shear of 5 - 15 knots is predicted along 92L's path over the coming five days, which may allow the storm to organize if it can handle the dry air surrounding it. The latest 00Z and 06Z model runs of the four best models for predicting tropical storm formation (GFS, ECMWF, NOGAPS, and UKMET) show weak development or no development of 92L, and NHC gave 92L a 30% chance of developing into a tropical depression by Monday morning in their 8am outlook. A west-northwest to northwest motion for 92L is predicted by all of the models, which should bring the storm close to Bermuda on Tuesday. 92L should then curve north and northeastwards out to sea.

93L
The disturbance Invest 93L, located near 12°N 35°W, midway between the Lesser Antilles Islands and the coast of Africa, has fallen apart over the past day. Recent visible satellite loops show almost no heavy thunderstorms and very little spin to the system. Dry air to the west and north, combined with moderate wind shear of 10 - 20 knots, have significantly disrupted 93L. The latest 06Z runs of the GFS and NOGAPS models do not show development of 93L, and neither do the latest 00Z runs of the ECMWF and UKMET models. NHC has reduced their odds of development of 93L to 10%. The system should find itself in an environment with lower wind shear on Sunday, and may be able to begin organizing again then. The storm should move through the Lesser Antilles Islands Tuesday or Wednesday.

Next post
I'll have a new post by 2pm Sunday.

Jeff Masters

Hurricane

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Four invests in the Atlantic; fair weather in Arctic to drive rapid sea ice loss

By: JeffMasters, 03:38 PM GMT die 12o August, anno 2011

It's a busy day in the tropical Atlantic, with the National Hurricane Center tracking four areas of interest (Invests.) None of these systems is a danger to any land areas over the next three days. The disturbance of most concern is the one farthest from land, a tropical wave that emerged from the coast of Africa two days ago. This wave, (Invest 93L), is located about 500 miles southwest of the Cape Verde Islands, and is moving westward at 15 - 20 mph. Recent visible satellite loops show that 93L has lost some of its heavy thunderstorms since yesterday, and the system is poorly organized, though there is a good deal of spin to the system. There is dry air to its north that is interfering with development. The SHIPS model and University of Wisconsin CIMSS wind shear analysis are showing high wind shear in excess 20 knots affecting 93L, which has undoubtedly contributed to the storm's loss of organization. Sea surface temperatures are 27.5°C, which is one degree above the 26.5°C threshold usually needed to support a tropical storm.


Figure 1. Morning satellite photo of the four Invests in the Atlantic today.

Forecast for 93L
High wind shear above 20 knots is predicted along 93L's path through Saturday afternoon, followed by a drop to the moderate range, 10 - 20 knots, for the succeeding four days. This should allow the storm to organize over the weekend. The latest 00Z and 06Z model runs of the four best models for predicting tropical storm formation (GFS, ECMWF, NOGAPS, and UKMET), have only one model, the GFS, that is indicating significant development of 93L. This model brings 93L near the northern Lesser Antilles Islands by Wednesday. NHC gave 93L a 40% chance of developing into a tropical depression by Sunday morning in their 8am outlook. Given 93L's recent struggles, I'd put these odds at 30%.

92L
An African wave midway between the northern Lesser Antilles Islands and the coast of Africa, near 18°N 45°W, is moving west-northwest at 20 mph. This system, (Invest 92L), is being given a 40% chance of development by NHC. Recent visible satellite loops show a modest amount of heavy thunderstorm activity, but no signs of a surface circulation. A Windsat pass from 8:04 am EDT this morning also showed no surface circulation, and noted top winds of around 35 mph. Water vapor satellite loops show that a large area of dry air surrounds 92L, and this dry air is causing problems for the storm. The SHIPS model and University of Wisconsin CIMSS wind shear analysis are showing moderate wind shear of 10 - 20 knots affecting 92L. Sea surface temperatures are 27 - 27.5°C, which is a degree above the 26.5°C threshold usually needed to support a tropical storm.

Forecast for 92L
Moderate wind shear of 10 - 20 knots is predicted along 92L's path over the coming five days, which should allow the storm to organize if it can handle the dry air surrounding it. The latest 00Z and 06Z model runs of the four best models for predicting tropical storm formation (GFS, ECMWF, NOGAPS, and UKMET) show weak development or no development of 92L, and NHC gave 92L a 40% chance of developing into a tropical depression by Sunday morning in their 8am outlook. A steady west-northwest motion for 92L is predicted by all of the models, which should make the storm miss the Lesser Antilles by a comfortable margin. However, Bermuda may be at risk from 92L next week.

94L
A broad low pressure system about 700 miles northeast of the northern Lesser Antilles Islands has developed a small amount of heavy thunderstorm activity, and may be a threat to become a tropical depression early next week. This system, (Invest 94L), is currently headed west-southwest at 10 mph, but is expected to turn northwest later today. Recent visible satellite loops show some spin to the cloud pattern at middle levels of the atmosphere, but no signs of a surface circulation. This system is also battling dry air, which is keeping the its heavy thunderstorms relatively meager. The SHIPS model is showing moderate wind shear of 10 - 20 knots affecting 94L. Sea surface temperatures are 28°C.

Forecast for 94L
Moderate wind shear of 10 - 20 knots is predicted along 94L's path over the coming five days, which should allow slow development, if it can handle the dry air surrounding it. None of our reliable models for predicting tropical storm formation (GFS, ECMWF, NOGAPS, and UKMET) show no development of 94L, and NHC gave 94L just a 20% chance of developing into a tropical depression by Sunday morning in their 8am outlook. Bermuda is the only land area that needs to be concerned with 94L.

95L
The final invest out there is an area of disturbed weather along on old frontal boundary several hundred miles off the coast of North Carolina. This sytem, Invest 95L, is headed northeastwards out to sea, and is not a threat to any land areas.



Figure 2. Arctic sea ice extent on August 11, 2011, was the 2nd lowest on record for the date. The Northeast Passage and Northwest Passage (southern route) were both ice-free. Image credit: UIUC Cryosphere Today.

Arctic sea ice poised to undergo record decline in mid-August
A strong high pressure system with a central pressure of 1035 mb has developed over the Arctic north of Alaska, and will bring clear skies and warm southerly winds to northeast Siberia and the Arctic during the coming week, accelerating Arctic sea ice loss. Widespread areas of northeastern Siberia are expected to see air temperatures 4 - 12°C (7 - 22°F) above average during the coming week, and the clockwise flow of air around the high pressure system centered north of Alaska will pump this warm air into the Arctic. Arctic sea ice extent, currently slightly higher than the record low values set in 2007, should fall to to its lowest extent for the date by the third week of August as the clear skies and warm southerly winds melt ice and push it away from the coast of Siberia. This weather pattern, known as the Arctic Dipole, was also responsible for the record sea ice loss in 2007, but was stronger that year. The weather conditions that led to the 2007 record were quite extreme--one 2008 study led by Jennifer Kay of the National Center for Atmospheric Research showed that 2007's combination of high pressure and sunny skies in the Arctic occur, on average, only once every 10 - 20 years. The 2011 summer weather pattern in the Arctic has not been nearly as extreme as in 2007, but the total sea ice volume has declined significantly since 2007, leading to much loss of old, thick, multi-year ice, making it easier to set a new low extent record with less extreme weather conditions. The GFS model is predicting that the Arctic Dipole will weaken by 8 - 15 days from now, with cloudier weather and weaker high pressure over the Arctic. This should slow down the rate of Arctic sea ice loss to very near the record low values observed in 2007. It remains to be seen if 2011 Arctic sea ice extent will surpass the all-time low set in September 2007; it will be close, and will depend on the weather conditions of late August and early September, which are not predictable at this time. It is already possible to sail completely around the North Pole in ice-free waters through the Northeast Passage and Northwest Passage, according to sea ice maps maintained by the UIUC Cryosphere Today website. This marks the fourth consecutive year--and the fourth time in recorded history--both of these Arctic shipping routes have melted free. Mariners have been attempting to sail these passages since 1497. This year, the Northeast Passage along the north coast of Russia melted free several weeks earlier than its previous record early opening.

Next post
I'll have a new post by 1pm Saturday.

Jeff Masters

Climate Change Sea Ice Hurricane

Updated: 03:39 PM GMT die 12o August, anno 2011

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Two African waves, 92L and 93L, worth watching

By: JeffMasters, 02:59 PM GMT die 11o August, anno 2011

An African wave is near 13°N 35°W, about 700 miles west-southwest of the Cape Verde Islands. This system, (Invest 92L), is moving west to west-northwest at 10 - 15 mph, and has the potential to develop into a tropical depression or tropical storm before arriving near the northern Lesser Antilles Islands early next week. Recent visible satellite loops show that 92L has less heavy thunderstorm activity near where it is trying to develop its circulation center than yesterday. Water vapor satellite loops that a large area of dry air lies just to the west of 92L, but the atmosphere in the immediate vicinity of 92L is moist. Even so, the decline of heavy thunderstorm activity since yesterday implies that dry air is probably working its way into 92L. The SHIPS model and University of Wisconsin CIMSS wind shear analysis are showing moderate wind shear of 10 - 15 knots affecting 92L. Sea surface temperatures are 26.5° - 27°C, which is very close to the 26.5°C threshold usually needed to support a tropical storm.


Figure 1. Morning satellite photo of Invest 92L and Invest 93L.

Forecast for 92L
Low to moderate wind shear of 5 - 15 knots is predicted along 92L's path over the coming three days, which should allow the storm to organize, assuming it can shut out any incursions of dry air that might intrude. The latest 00Z and 06Z model runs of the four best models for predicting tropical storm formation (GFS, ECMWF, NOGAPS, and UKMET) show weak development or no development of 92L, and NHC gave 92L a 30% chance of developing into a tropical depression by Saturday morning in their 8am outlook. A steady west to west-northwest motion for 92L is predicted by all of the models, which would put the storm in the vicinity of the northern Lesser Antilles Islands by Sunday. On Saturday and Sunday, 92L is expected to enter a region where an upper-level low pressure system will bring high wind shear of 20 knots to the storm, which should slow development. This upper-level low is also expected to turn 92L more to the northwest, so the storm is likely to pass north of the Lesser Antilles, though may pass close enough to give heavy rains to the northernmost islands. It is too early to know if 92L will recurve out to sea and potentially threaten Bermuda, or continue to the northwest towards the U.S. East Coast.

93L
An African wave that emerged off the coast of Africa is near 10°N 22°W, a few hundred miles south of the Cape Verde Islands. This system, (Invest 93L), is also moving west at 10 - 15 mph, and has the potential to develop into a tropical depression or tropical storm before arriving near the northern Lesser Antilles Islands near the middle of next week. Recent visible satellite loops show that 93L has a decent amount of heavy thunderstorms, but this activity is not well organized. There is not much spin associated with 93L yet. 93L is fairly well-protected from dry air to its north and west. The SHIPS model and University of Wisconsin CIMSS wind shear analysis are showing moderate wind shear of 10 - 20 knots affecting 93L. Sea surface temperatures are 27.5°C, which is one degree above the 26.5°C threshold usually needed to support a tropical storm.

Forecast for 93L
Moderate wind shear below 20 knots is predicted along 93L's path over the coming five days, which should allow the storm to steadily organize. 93L is about 600 miles east of 92L, which is close enough that the two systems may interfere with each others' organization. The latest 00Z and 06Z model runs of the four best models for predicting tropical storm formation (GFS, ECMWF, NOGAPS, and UKMET), have only one model, the GFS, that is indicating significant development of 93L. This model brings 93L near the northern Lesser Antilles Islands by Wednesday. NHC gave 93L a 20% chance of developing into a tropical depression by Saturday morning in their 8am outlook. Due to moister air, the potential for less wind shear, and a more southerly track, 93L is probably a greater threat to the Lesser Antilles than 92L.

Jeff Masters

Hurricane

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Two African waves that may develop

By: JeffMasters, 04:59 PM GMT die 10o August, anno 2011

Hello everyone, it's Jeff Masters back with you again after a long stretch of vacation. Now that the peak part of hurricane season is upon us, I'll be with you every day for the next few months, in what promises to be an unusually active Atlantic hurricane season. We've got several threats to talk about today, most notably a strong African wave near 12.5°N 30.5°W, about 400 miles west-southwest of the Cape Verde Islands. This system, dubbed Invest 92L by NHC, is moving west to west-northwest at 10 - 15 mph, and has the potential to develop into a tropical depression or tropical storm before arriving near the northern Lesser Antilles Islands early next week. Recent visible satellite loops show that 92L is beginning to develop a surface circulation, and heavy thunderstorms are slowly building along the western edge of the center. However, a separate area of heavy thunderstorms lies 400 miles to the east, just south of the Cape Verde Islands, and this blob is interfering with consolidation of the center near the blob of heavy thunderstorms at 30.5°W. Water vapor satellite loops show that a large area of dry air from Africa lies just to the west of 92L, but the atmosphere in the immediate vicinity of 92L is moist, so dry air is currently not a problem for the storm. The SHIPS model is diagnosing low shear, 5 - 10 knots, over 92L, but the University of Wisconsin CIMSS analysis shows that moderate shear of 10 - 20 knots is affecting 92L. Sea surface temperatures are 26.5° - 27°C, which is very close to the 26.5°C threshold usually needed to support a tropical storm.


Figure 1. Noon satellite photo of Invest 92L.

Forecast for 92L
Low to moderate wind shear of 5 - 15 knots is predicted along 92L's path over the coming three days, which should allow the storm to steadily organize, assuming it can shut out any incursions of dry air that might intrude. The latest 00Z and 06Z model runs of the four best models for predicting tropical storm formation (GFS, ECMWF, NOGAPS, and UKMET) show little or no development of 92L, and NHC gave 92L just a 20% chance of developing into a tropical depression by Friday morning in their 8am outlook. Given the recent improvement in the satellite appearance of 92L, I would put these odds at 30%. A steady west to west-northwest motion for 92L is predicted by all of the models, which would put the storm in the vicinity of the northern Lesser Antilles Islands by Sunday. On Saturday and Sunday, 92L is expected to enter a region where an upper-level low pressure system will bring high wind shear of 20 knots to the storm, which should slow development. This upper-level low is also expected to turn 92L more to the northwest, so the storm may pass north of the Lesser Antilles. It is too early to know if 92L will recurve out to sea and potentially threaten Bermuda, or continue to the northwest towards the U.S. East Coast.


Figure 2. NASA MODIS image taken at 10:40am EDT 8/10/11 of the tropical wave emerging from the coast of Africa. The GFS model is predicting this system will develop into a tropical storm early next week. Image credit: NASA.

Tropical wave emerging from the coast of Africa
A strong tropical wave currently emerging from the coast of Africa near 8°N has a modest amount of spin and heavy thunderstorm activity associated with it, and has the potential to develop early next week once it moves past the Cape Verde Islands. The GFS model has been developing this system into a tropical storm in several of its recent runs. A westerly track towards the Lesser Antilles is expected by the GFS model.

Jeff Masters

Hurricane

Updated: 05:45 PM GMT die 10o August, anno 2011

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July 2011: Most extreme July on record for the U.S.

By: JeffMasters, 04:43 PM GMT die 09o August, anno 2011

According to the National Climatic Data Center's Climate Extremes Index, July 2011 was the most extreme July on record (since 1910) with a value of 37%. The Climate Extremes Index is created by merging the various climate indicators (drought, flood, extreme heat, extreme cold, etc.) into an index that can be tracked over time. This month's record CEI was due to extreme warm minimum temperatures across the country, wet northern Plains and Great Lakes, extreme warm maximum temperatures, and the severe drought across the South and Gulf Coast.

It was the fourth warmest July on record for the nation, and the fourth warmest month overall with an average temperature of 77°F. Extreme heat continued to bake the South, and Oklahoma and Texas both had their warmest months on record. Oklahoma's statewide average temperature was a remarkable 88.9°F in July, which is the warmest monthly statewide average for any state in any month. Dallas, Texas hit or exceeded 100°F on 30 out of the 31 days in July. For the entire South climate region, which comprises Texas, Oklahoma, Kansas, Louisiana, Arkansas, and Mississippi, July 2011 was the warmest month on record for any of the climate regions.

As we noted in a previous blog, an unprecedented area of exceptional drought covered the United States in July, the largest area in the history of the U.S. Drought Monitor. 75% of Texas was in an exceptional drought, and the entire state of Oklahoma was in moderate to exceptional drought in July. The NCDC estimates that it would take 20 inches of rain to end the drought in one month in the worst hit areas of Oklahoma and Texas.


Figure 1. Texas and Oklahoma had its hottest and the state of Washington had its 11th coolest July on record last month, according to the NCDC.


Figure 2. Texas had its second driest July on record, and Oklahoma had its 9th driest according to the NCDC. California continues to be wetter than average, and last month was its 8th wettest July on record.

Angela

Climate Summaries Drought Heat

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Record Low Arctic Sea Ice for July; Quiet tropics

By: JeffMasters, 05:26 PM GMT die 08o August, anno 2011

Last month, Arctic sea ice extent was the lowest ever recorded for any July in the 1979 to 2011 satellite record, according to the National Snow and Ice Data Center. Most of the ice loss occurred in the first half of the month when high pressure made for clear skies and melting sunshine, and warm air blew into the Arctic from the south. In the first two weeks of July, air temperature over the North Pole was 11 to 14 degrees Fahrenheit above average. During the last two weeks of July, low pressure took over and brought cooler temperatures, although it appears this also acted to push the ice around, which resulted in a larger but thinner area of ice. New research shows that old ice continues to decline as well, which is problematic because older ice is more stable and tends to grow thicker over multiple seasons, and new ice is thin and more susceptible to melting. According to the University of Washington Polar Science Center, Arctic sea ice volume was 51% lower than average and 62% lower than the maximum (which was seen in 1979 at the beginning of the record).


Figure 1. Monthly July ice extent from 1979 to 2011 from the National Snow and Ice Data Center shows a 6.8% decline per decade.

The low amount of sea ice along Siberia has opened up the Northern Sea Route early (figure 2), and some companies are already taking advantage. It doesn't appear possible to get through the whole passage without the aid of an ice breaker or two around the East Siberian Sea, but compared to the normal route south through the Mediterranean and Indian Ocean, it's a deal. From Yokohama, Japan to the Rotterdam port in the Netherlands, the route through the Arctic is around 8,500 miles. If the Arctic is impassable, the route through the Pacific, Indian, and Atlantic oceans is around 13,000 miles.


Figure 2. Sea ice concentration from the University of Illinois Polar Research Group. Image modified to highlight the Northern Sea Route in light blue.

Quiet Tropics

After a brief reformation over the weekend as a tropical depression, Emily finally dissipated for good on Sunday, and the National Hurricane Center issued its last advisory on the system. The 7-day precipitation accumulation for July 30th through August 5th (figure 3) shows us that most of Hispaniola and eastern Cuba dodged the widespread, extreme rain that could have fallen had Emily stayed organized. Locally high accumulation of 5 to 15 inches fell in the Dominican Republic, which was probably aided by topography, but it does not appear that heavy, widespread rain fell in Haiti. The southeast Bahamas also might have also seen some relatively heavy rain (1.5 to 5 inches) from the system as it redeveloped thunderstorm activity north of Cuba late last week.


Figure 3. Satellite-estimates precipitation in millimeters for the 7 days preceding Friday, August 5th. Data provided by the Climate Prediction Center.

Beyond Emily, we're seeing a typical upswing in African easterly wave activity for August. Out in the main development region of the Atlantic, between Africa and the Caribbean, we have two waves, one near 50°W and the other around 25°W. Neither of these waves are forecast by any models to develop into tropical cyclones at this point, but the National Hurricane Center did invest the eastern wave over the weekend as 92L. They're no longer updating that invest as of yesterday afternoon, since satellite presentation degraded and the GFS stopped developing the wave. Even though they aren't favored to develop, what these systems might provide is a primer for waves that have yet to leave Africa. The next two waves, scheduled to enter the Atlantic around August 11th and August 15th, are looking slightly more favorable, although model support has waned since last week. This is expected though—its hard to get consensus and consistency from models on waves that have yet to enter open water. We'll know more at the end of this week, for sure.

Angela

Climate Change Sea Ice

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Tropical Depression Emily Reforms, Rain for the Bahamas

By: JeffMasters, 04:28 AM GMT die 07o August, anno 2011

As of 11PM EDT, Tropical Depression Emily was located at 27.4N, 78.2W, 70 miles NNE of Freeport, Grand Bahama Island. It was moving north at 8 mph with sustained winds of 35 mph and a minimum central pressure of 1011 mb. No watches or warnings are in effect for Emily at this time.


Figure 1 IR satellite view of Emily taken at 1200AM EDT, August 7, 2011

The remnants of Tropical Storm Emily were recognized as a tropical depression after analysis of surface observations, satellite imagery, and Hurricane Hunter flights showed that Emily had achieved a closed circulation again. However, at this time, it is not expected to do much beyond raining heavily (1-3 inches, 6 inches in isolated regions) over the Bahamas. As Figure 2 shows, NHC forecasts Emily to move north and then sharply eastwards before dissipating as it merges with a front. The westerly wind shear associated with this front will be the likely cause for Emily's second demise.


Figure 2 Official track forecast of Emily.

As Figure 3 shows, the concerns for rain from Emily is justified based on past behavior. Satellite estimates shows that on August 4, 3-5 inches of rain fell just south of Hispaniola, with 1-2 inches falling on the southern Dominican Republic.


Figure 3 Satellite-estimated precipitation (mm) for Thursday, August 4 using the CMORPH techniques. Data provided by the Climate Prediction Center

If the situation warrants, we will have a new blog entry Sunday. Otherwise, we will resume the normal posting schedule on Monday.

Thanks for reading,

Dr. Rob Carver

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Remnants of Emily could redevelop; Muifa batters Okinawa; Central U.S. roasts

By: JeffMasters, 04:54 PM GMT die 05o August, anno 2011

Tropical Storm Emily degraded into an open tropical wave yesterday afternoon, after Hurricane Hunters could no longer locate a center of circulation at the surface. Through the morning yesterday, the storm appeared to lose most of its strong thunderstorm activity on the north side, and mid-level circulation was broad (tropical cyclones need a tight, coherent circulation to maintain themselves). Soon after the Hurricane Hunters took a pass through the storm, the National Hurricane Center demoted Emily from a tropical storm to a remnant low, while continuing to stress the rainfall threat to Hispaniola and eastern Cuba. Today it appears the center of the remnants are located just north of eastern Cuba in the southern Bahamas, although thunderstorm activity continues across eastern Cuba. Hispaniola probably saw rain and thunderstorms again early this morning, the strongest of which were on the eastern side of the island. New thunderstorm activity is starting to develop in the southeast Bahamas. Given Wednesday's rain gauge analysis from CPC, Hispaniola probably saw at least an additional 5 inches of rain yesterday.

Environmental conditions remain pretty much the same as yesterday, but are expected to become more favorable for Emily's remnants, and redevelopment of the storm is possible. Circulation from the low to mid-levels is still broad and tilting to the east with height due to the lingering moderate westerly wind shear. However, this shear is expected to dissipate some over the next 24 hours, and signs of this are already present to the west of the remnants. The dry air that has been following the storm since its inception has dissipated, as well.


Figure 1. Satellite imagery of the remnants of Tropical Storm Emily as they move northwest away from Cuba and Hispaniola and into the Bahamas.

Forecast for Emily's Remnants
Interestingly, the models have come into better agreement on the forecast for former Emily now that it has lost its surface circulation and degenerated into a tropical wave. The ECMWF, which has come out ahead in this forecasting game so far, is optimistic today that Emily will redevelop. Other global models—GFS, CMC, and FIM—also redevelop the storm. Consensus on timing of redevelopment seems to be when the wave reaches the northern Bahamas in 24 to 48 hours. At 12Z (8am EDT), the high-resolution HWRF model run forecasted a track that was furthest to the west of all the models, scraping eastern Florida as it travels northwest. The most probable track and intensity forecast that I see at this point is north-northwest movement over the next 24 to 36 hours, at which point the system will take a fairly sharp turn to the northeast and out to sea. Without an already established, coherent circulation, it appears unlikely that if Emily is reborn it will intensify into anything more than a moderate tropical storm. However, there is some potential as the system moves out to see that it could gain some strength and develop hurricane-force winds before it transitions into an extra-tropical cyclone.

Typhoon Muifa passes to the south of Okinawa, heads into East China Sea

The center of Typhoon Muifa passed to the south of Okinawa earlier this morning (Eastern time) and it continues to batter the islands with high winds and torrential rain. Local radar estimate rainfall rates as high as 80 mm/hour (approx. 3 inches/hour) in the strongest rain bands. Kadena Air Force Base near the city of Okinawa has been reporting sustained winds of 47 mph with gusts up to 72 mph. Muifa is expected to turn northwest today as it enters the East China Sea as a category 1 on the Saffir-Simpson scale, and then intensify into a category 2 as it passes close to eastern China. This morning, the forecast is that Muifa will probably not make landfall anywhere as a typhoon.


Figure 2. Radar imagery from the Japan Meteorological Agency around 1am JST. Scale is in millimeters. Highest rainfall rates appear to be approximately 3 inches/hour.

South-Central U.S. continues to bake

The extreme heat continues again today after 269 high maximum and 250 high minimum temperature records were set yesterday, 19 and 29 of which were all-time records, respectively. 206 of yesterday's records were 110°F or higher. Yesterday, Reuters was reporting that Texas was one power plant shutdown away from rolling blackouts. The forecast today doesn't look any better. Heat index values up to 125° are forecast in eastern Texas and the Lower Mississippi Valley.

Particularly toasty heat index values from yesterday:

• Mobile, Alabama: 120°
• Arkadelphia, Arkansas: 121°
• Bay St. Louis, Mississippi: 121°
• Memphis, Tennessee: 122°


Figure 3. Heat index forecast from the ECMWF for today. Scale is in degrees Fahrenheit. You can plot model forecasts using Wundermap by choosing the "Model Data" layer.

Angela

Heat Hurricane

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Tropical Storm Emily continues to threaten Haiti; More extreme heat in Central U.S.

By: JeffMasters, 04:47 PM GMT die 04o August, anno 2011

Tropical Storm Emily remains unorganized this morning, and continues to linger just south of Haiti, near 17.3°N, 72.3°W. Emily is 90 miles south of Port au Prince, Haiti. Storm motion over the past 24 hours has been slow, varying between completely stopped and west to west-northwest at 5 mph. This motion (or lack thereof) is still something that the models aren't analyzing well. Satellite imagery shows that thunderstorm activity on the north side of Emily seems to be disrupted, possibly by the terrain of Hispaniola, but also potentially by the continued moderate shear to the north of the storm. Wind shear has weakened to the northwest of the storm in the past 24 hours, but it will probably not be enough to allow Emily to undergo any significant intensification. The layer of dry air that we've been talking about for the past few days has also all but dissipated to the west and north of the storm. As the National Hurricane Center has been forecasting, environmental conditions are becoming slightly more favorable for the storm. Satellite estimates of wind motion suggest that low level circulation in the storm has become very broad and extends north over Hispaniola, which indicates that there's potential for the storm to undergo a quick jump to the north, but overall the storm remains weak and this seems unlikely. Emily continues to be tilted to the east with height, but doesn't appear as sheared as yesterday morning.

Conditions in Hispaniola have surely deteriorated over the past 24 hours, however, thunderstorm activity appears to have weakened over the island this morning. Infrared satellite imagery shows that cloud tops have warmed in the past 6 hours on the north side of the storm, which means that strong thunderstorms are no longer building high into the atmosphere. High resolution model forecasts (see Figure 1) have continued to predict that the heaviest rain will fall to the east of the storm. The longer Emily tracks west without taking a significant turn to the northwest, the more likely it is that Haiti will see the most extreme rainfall in the storm. Overall, 6 to 12 inches of rain is expected to fall, with local amounts up to 20 inches possible in higher terrain. Flash floods and mudslides are a serious threat.


Figure 1. Forecast radar and sea level pressure from the 06Z (2am EDT) run of the HWRF high resolution model. While I think that the model was initialized poorly and doesn't accurately represent where the storm will travel over the next 24 hours, I do think that the precipitation field is accurate. The strongest rain and winds have been on the east and north sides of the storm over the past couple of days. If Emily continues to move west before taking a significant turn to the northwest, Haiti could receive the strongest impact from the storm.

Forecast for Tropical Storm Emily
Models continue to waver back and forth on Emily's forecast track. Yesterday evening, the HWRF model forecast Emily to cross over Hispaniola and undergoing a close encounter with the Florida coastline. Last night, the National Hurricane Center wrote that "if Emily does not begin its northwestward turn soon…a watch could be required for parts of southern Florida today." Since the storm appears to be moving slightly more to the north than west this morning, this doesn't look like it will be necessary, although the forecast remains very uncertain. In today's 06Z runs, both the HWRF and the GFDL are probably forecasting Emily to move too far north in the next 12 hours. Given the present direction and speed of the storm, it's hard to see these two models' forecasts coming to fruition. The official forecast track from the National Hurricane Center is a turn to the northwest over the next 6 to 12 hours, with landfall in Haiti happening this afternoon. Beyond that, they forecast Emily to stay on a northwest course through the Bahamas, where Emily could restrengthen a bit before making a turn to the northeast on Sunday, although they qualify this forecast with the fact that it's very uncertain, and that the global models dissipate Emily after crossing Hispaniola. The official forecast track does not have Emily making any landfall in Florida, but the Miami to West Palm Beach area is still within the cone of uncertainty.

Interestingly, the models that have done the best job at predicting the track of Emily thus far are the less relied-on statistical track models—those that don't take into account any current atmospheric dynamics. If Emily remains on a west to west-northwest track today, we cannot rule out that it cross over a larger area of Cuba, approaching the southeast portion of Florida. However, given the amount of land interaction in this potential track, the probability of Emily remaining a tropical cyclone in this scenario is low.


Figure 2. Satellite imagery of Tropical Storm Emily at 10:15am EDT. The strongest thunderstorm activity is now in the southern portion of the storm. Thunderstorms over Hispaniola appeared to weaken this morning.

Typhoon Muifa

Typhoon Muifa continues to be a category 2 typhoon on the Saffir-Simpson scale. Satellite imagery shows a well developed storm that is moving west-northwest. Over the next day, Muifa is expect to turn to the northwest as it approaches China. Today's track forecast is more north and east of yesterday's, with a brief landfall just north of Shanghai, potentially as a category 3.


Figure 3. MODIS satellite imagery of Typhoon Muifa from earlier today, plotted using NASA's new Rapid Response Web Mapping Service.

Central U.S. heatwave

The heat continues for the central U.S., where I've heard reports that local media in the region were canceling all of their outdoor shots because of the dangerous conditions. Here are some of yesterday's extreme temperatures, which were compiled by our weather historian, Christopher C. Burt:

Little Rock, Arkansas set an all-time record with 114°F (the old record was 112°F set in 1986). Fort Smith, Arkansas set an all time record of 115°F (the old record was 113°F set both Tuesday and previously in 1936).

State maximum air temperatures from Wednesday:

• Arkansas: 116° at Silver Hill (4° short of state all-time record)
• Oklahoma: 115° at Atoka
• Louisiana: 111° at Caney
• Texas: 111° at Fort Worth and Wichita Falls (that also had a record high minimum of 88° this morning)
• Missouri: 109° at Branson and Ava

The heat index is also at play in this heat wave; some incredible values recorded yesterday include 126° in Poplar Bluff, Missouri, 125° in Walnut Ridge, Arkansas, and 122° in Arkadelphia, Arkansas. The GFS continues to forecast heat index values around 120° in the lower Mississippi Valley through the weekend.

Angela

Heat Hurricane

Updated: 04:48 PM GMT die 04o August, anno 2011

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Emily slides west, still a threat for Hispaniola and Cuba

By: JeffMasters, 07:37 AM GMT die 04o August, anno 2011

As of 2AM EDT, Tropical Storm Emily was located at 17.1N, 71.3W, about 120 miles south-southeast of Port-au-Prince, Haiti. Emily was moving W at 5 mph with sustained winds of 50 mph. It's central pressure was estimated to be 1006 mb. Tropical storm warnings are in effect for the Dominican Republic, Haiti, the southeast and central Bahamas, the Turks and Caicos islands, and eastern Cuba.

Satellite imagery still shows that the majority of convection associated with Emily is east of the center of circulation.


Figure 1 IR Satellite image of TS Emily taken at 2AM EDT August 4, 2011

Emily and the Turn Northwards

According to the most recent forecast issued by NHC, Emily was forecast to be at 17.5N, 72.5W at 2AM EDT, which is a point 68 miles west-northwest of it's assigned location. This indicates that Emily is not curving northwards as expected. This makes me more skeptical of the computer model forecasts that pull Emily to the northwards sharply towards the southeast coast of Florida before recurving out to sea. All of the 00Z global models (NOGAPS, GFS, and CMC) are in rough agreement.

The forecast tracks provided by the suite of simpler models, the Beta and Advection Models and CLIPER, disagree. They have Emily taking a much more gradual turn to the north, thus moving northwest across Cuba. Given that these models have done a better job of predicting Emily's westwards track, I'm inclined to place more confidence in their predictions. However, the further west Emily goes, the chance that Emily makes landfall in Florida (due to a recurve) goes up. People with interests in Cuba and south Florida should keep an eye on this storm.

My opinion about forecasting Emily's intensity has not changed significantly from last evening's update. If Emily's circulation can survive the mountains of Hispaniola and/or the terrain of Cuba, conditions are favorable for moderate intensification.

The current NHC forecast is shown in Figure 2 and has Emily turning towards the north, passing through the western Bahamas before turning out to sea.

In terms of immediate impacts, 6-12 inches of rain are expected over Haiti, and the Dominican Republic, with 20 inches possible in isolated areas. Flash floods and landslides are expected to be major problems on Hispaniola. Tropical storm winds will reach Haiti today and could reach eastern Cuba later today. Port-au-Prince, Guantanamo and Santiago de Cuba would be good stations to monitor today.


Figure 2 Official five-day track forecast for Tropical Storm Emily.

Eastern Pacific

Eugene reached category 4 status with estimated winds of 140 mph earlier today. After that peak, Eugene started weakening and now has winds of 120 mph. Further weakening is expected as Eugene moves over cooler waters. Invest 97E is not looking as impressive as it was last night and has a 20% chance of becoming a tropical disturbance in the next 48 hours.

Western Pacific

Typhoon Muifa is now forecast to make landfall near Shanghai, China as the equivalent of a category 3 hurricane. This will be troublesome for one of the busiest ports in the world.


Figure 3 Five-day track forecast for Typhoon Muifa from the Joint Typhoon Warning Center.

Angela will have a full post Thursday morning discussing Emily.

Thanks for reading,

Dr. Rob Carver

Updated: 07:38 AM GMT die 04o August, anno 2011

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Tropical Storm Emily stalls, remains a threat to Hispaniola

By: JeffMasters, 12:37 AM GMT die 04o August, anno 2011

All afternoon, Tropical Storm Emily has remained on a westward track with maximum sustained winds of 50 mph. In the 8pm EDT update from the National Hurricane Center, the storm was nearly stationary, with no forward movement. The storm gained some thunderstorm activity over its center of circulation throughout the day, but remains sheared to the east. In order for tropical cyclones to intensify (or, continue to exist at all), they need to be vertically stacked and standing straight up in the atmosphere. Emily continues to be tilted east due to 20 knots of westerly wind shear, which is apparent on satellite and also in recent satellite analysis of upper-level circulation.

Emily's tropical storm-force winds extend 115 miles to the north and east of the center, and tropical storm conditions are probably already being felt in Hispaniola. Isolated rainfall amounts of up to 20 inches are expected on the eastern side of the storm. The longer Emily tracks west before making a turn to the northwest, the more likely it is that Haiti will see the heavier rainfall amounts. In any case, Emily is a serious threat for flash flooding and mudslides on the island of Hispaniola and eastern Cuba.


Figure 1. MODIS satellite imagery from earlier today, plotted using NASA's new Rapid Response Web Mapping Service.

Forecast for Tropical Storm Emily
The forecast for Emily remains similar to this morning's update, with a slight shift to the east in track. The National Hurricane Center forecasts that the storm will make landfall in Haiti overnight tonight or early tomorrow as a tropical storm. After that, it will continue on a track to the northwest until Saturday, when it will turn to the northeast and out to sea. This is all assuming Emily makes the turn to the northwest over the next 12 hours.

This afternoon the HWRF and GFDL shifted their forecast track slightly to the east away from the Florida coast. Consensus shifted this way as well, and that change is also present in the official forecast track. As the storm moves north of Hispaniola and Cuba, environmental conditions will become more favorable, and the storm could gain some organization. But this is very hard to predict since Emily hasn't actually made a turn to the northwest, yet. Furthermore, the longer Emily tracks to the west, the more of a threat it becomes to the Florida coast.

Typhoon Muifa a landfall threat for China coast

Typhoon Muifa has sustained winds of 109 mph, with gusts up to 132 mph, and is a category 2 on the Saffir-Simpson Hurricane Scale. Muifa's concentric eyewalls are plainly visible on both infrared satellite imagery as well as radar, which is indicative of a mature, intense cyclone undergoing eyewall replacement cycles. Typhoon Muifa is expected to remain a category 2 with winds of at least 104 mph through mid-day Saturday, at which point it is forecast to intensify slightly to a category 3 as it approaches the China coast. As of this afternoon, Muifa is expected to make landfall south of Shanghai, near Zhoushan, Saturday afternoon or evening (local time). In addition to being a serious threat to all of the involved coastal cities, this is a particularly dangerous track for Shanghai and Hangzhou, since near-hurricane-strength winds will be out of the east, pushing water into the surrounding inlets. The forecast landfall location has been trending south along the coast, so it doesn't appear that China will be able to escape a Muifa landfall.


Figure 2. Infrared satellite imagery of Typhoon Muifa from August 3rd.

Dr. Carver will have an update later tonight should there be any interesting changes to Emily or the forecast. I'll be back tomorrow with another post.

Angela

Hurricane

Updated: 12:40 AM GMT die 04o August, anno 2011

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High wind shear disrupts Emily as it approaches Hispaniola

By: JeffMasters, 05:06 PM GMT die 03o August, anno 2011

In defiance to its forecast, Tropical Storm Emily continues to move due west this morning, and we wonder just how far west it will get before turning toward Hispaniola. Recent Hurricane Hunter missions have shown that Emily is still very poorly organized, and although the center of circulation is plainly obvious on satellite imagery, it's only because it is so displaced from the thunderstorm activity. Wind shear around the storm is just high enough, around 20 knots out of the west, to push the upper levels of circulation and thunderstorm activity to the east, exposing the surface low. In order for tropical cyclones to intensify (or, continue to exist at all), they need to be vertically stacked and standing straight up in the atmosphere. Right now, Emily is tilting to the east. This is bad news for the organization of the storm, and something that Emily will have to work hard at recovering from. In addition to the wind shear, dry air continues to wrap around the north and west of the storm. This isn't as critical as unfavorable wind shear, but it's not helping to create new thunderstorm activity. The strongest winds of 50 mph were found to the north and east of the center this morning, and Emily is not expected to intensify before making landfall in Hispaniola, which is forecast for tonight. The HWRF is forecasting the strongest precipitation to fall on the northeast side of the storm as is passes over Hispaniola. This is relatively good news for Haiti, but the country could still receive up to 5 inches of rain, and since the models have been trending the track west over the past couple of runs, it's something to watch closely. No matter the scenario, Emily is expected to produce heavy rains, flash flooding, and mudslides in Haiti and the Dominican Republic, which are all to common on the mountainous island.


Figure 1. Forecast precipitation accumulation from the HWRF high resolution model's 6Z (2am EDT) run. The color contour scale is in inches. The coastlines are a thin, red line. The Dominican Republic is expected to get the most rain out of Emily. You can view the HWRF model runs on Wundermap.

Forecast for Tropical Storm Emily
The future of Emily remains uncertain, and even the National Hurricane Center is using the "if" word when forecasting Emily's track after crossing Hispaniola. "If" it makes it north of Hispaniola. Over the past couple of runs, the models have been trending their forecast tracks back to the west, most likely because Emily has remained on a westward track longer than expected. This is expected—the longer Emily remains shallow and unorganized, the longer it will track west. It will need to build up taller in the atmosphere to be influenced by the steering winds that can push it north. Given its westward track, today's models are likely closer to reality than what we've seen in the past couple of days. This morning, the CMC, UKMET, and HWRF models send Emily on a northwest track to Florida. This is a change from the past couple of days for the HWRF, but the CMC and UKMET have consistently been the western boundary of model consensus. THE GFDL has also taken a huge swing to the west, and now suggests it will come very close to a southeast Florida landfall. The ECMWF and GFS continue to forecast that Emily will take a harder turn north through the Bahamas, not reaching the Florida coast.


Figure 2. Satellite image of Tropical Storm Emily at 11:15am EDT. The surface circulation is visible to the west of the strongest thunderstorm activity.

Consensus of the models falls between the HWRF/GFDL solution and the ECMWF/GFS solution, and the National Hurricane Center continues to use the consensus for the official track forecast, which calls for Emily to take a turn to the northwest and make landfall in Hispaniola this afternoon, after which continuing northwest until Saturday morning when it's between the island of Grand Bahama and West Palm Beach, Florida. At this point, they expect the storm to jog north and then northeast.

Emily's intensity forecast continues highly dependent on the track it takes. Assuming it can survive the wrath of Hispaniola, Emily will enter slightly more favorable environmental conditions to the north of the islands. This is what the Hurricane Center is forecasting, although they remain cautious. There is a very good chance that, if Emily does turn northwest today, it will not be able to reorganize after crossing Hispaniola. If it does maintain organization, Emily could reach hurricane strength as it moves northeast out to the open Atlantic. The other scenario at this point is that the storm keeps moving west, which will be detrimental to its orgnization. The models that track Emily into the far eastern Gulf of Mexico don't suggest any reintensification—the CMC fizzles the system below tropical storm strength quickly, probably because of the long track over Cuba it would have to take. In any case, Emily remains a threat most certainly to Hispaniola, and potentially to Florida.

I'm planning a quick update later this afternoon/evening for an update on new model runs, and potential Hispaniola landfall.

Angela

Hurricane

Updated: 07:02 PM GMT die 09o January, anno 2012

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Tropical Storm Emily Approaches Hispaniola

By: JeffMasters, 04:04 AM GMT die 03o August, anno 2011

As of 8PM EDT, Tropical Storm Emily was located at 16.2N, 66.7W, moving WNW at 14 mph with sustained winds of 50 mph. It's central pressure was estimated to be 1005 mb. Tropical storm warnings are in effect for Puerto Rico, the Dominican Republic, Haiti, the southeast Bahamas, and the Turks and Caicos islands.

2AM EDT Update
As of 2AM EDT, Tropical Storm Emily was located at 16.3N, 67.5W, moving WNW at 13 mph with sustained winds of 50 mph. It's central pressure was estimated to be 1006 mb. Tropical storm warnings are in effect for Puerto Rico, the Dominican Republic, Haiti, the southeast Bahamas, and the Turks and Caicos islands.
End update

Satellite imagery shows a large amount of convection near Emily's center. However, the NHC discussion suggests that Emily is not standing straight up, like an ideal tropical cyclone, but the circulation is tilted eastwards with height. This is due to the wind shear present over the storm.


Figure 1 IR Satellite image of TS Emily taken at 11PM EDT August 2, 2011



Forecasting Emily
The fog of uncertainty still shrouds Emily's track forecast. The 12Z ECMWF and NOGAPS models keep Emily on a west to west-northwest track that skirts the southern edge of Hispaniola before running along the length of Cuba. The 12Z CMC global model has Emily tracking towards the NW, but recurving before making landfall along the US coastline. The 12Z and 18Z GFS runs (as shown in Figure 2), agree on a roughly similar track.


Figure 2 Peak winds (mph) over the next week from the 18Z GFS

The 12Z UKMET global model, and the 18Z GFDL and HWRF dynamical models are west of the GFS/CMC consensus track, withe the GFDL keeping Emily over the western Bahamas. The HWRF and UKMET tracks stay very close to the Florida/Georgia coastlines.

However, all of these tracks require Emily's circulation to grow tall enough that the upper-level steering winds can pull Emily towards the NW. I've discussed the situation with Angela Fritz, and she thinks that if Emily's circulation remains shallow, a more westerly track like that described by the ECMWF and NOGAPS could be more likely.

If we look at the previous NHC forecast, Emily was expected to be at 15.9N, 66.5W at the time of the forecast update. This is approximately 25 miles southeast of Emily's current position. If we ignore the uncertainty of locating Emily's center, this suggests that the westerly ECMWF/NOGAPS track is less likely, but doesn't say much about deciding between the GFS/GFDL and UKMET/HWRF tracks.

My opinion about forecasting Emily's intensity has not changed from this morning's update. I would prefer to wait for Emily after it has cleared the island of Hispanola and it's tall mountains. If Emily's circulation can survive the 8000 feet tall mountains of Hispaniola, the sea is warm enough for moderate intensification.

Having taken all of this into consideration, the 5 day NHC track forecast splits the difference between the HWRF/UKMET and GFS/GFDL tracks, bringing Emily over the central Bahamas before recurving towards the northeast. Emily is also forecast to become a hurricane on Sunday, August 7. However, it is important to remember that NHC has said that the forecast uncertainty after 48 hours is larger than usual for Emily. So, people living on the East Coast should still not think they are in the clear just yet.

In terms of immediate impacts, 4-6 inches of rain are expected over Puerto Rico, Haiti, and the Dominican Republic, with 10 inches possible in isolated areas.


Figure 2 Official five-day track forecast for Tropical Storm Emily.

Eastern Pacific

Eugene is now the third major hurricane of the Eastern Pacific season with estimated winds of 115 mph. However, Eugene is well out to sea and should not threaten any landmasses. Invest 97E has a 70% chance of becoming a tropical disturbance in the next 48 hours, but will likely not affect any land areas.

Angela will have a full post Wednesday morning discussing Emily.

Thanks for reading,

Dr. Rob Carver

Updated: 06:20 AM GMT die 04o August, anno 2011

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Tropical Storm Emily remains weak with roadblocks ahead

By: JeffMasters, 06:14 PM GMT die 02o August, anno 2011

Tropical Storm Emily took a moment to pause this morning, with no forward motion to speak of in the 11am EDT advisory from the National Hurricane Center, who say Emily might have been reorganizing. Emily eventually picked up some speed, and was moving west at 12 mph with maximum sustained winds of 45 mph in the 2pm EDT advisory. Satellite loops suggest that the storm has improved since yesterday, with strong thunderstorm activity surrounding the center of circulation accompanied by moderately strong outflow at higher levels. Recent satellite estimates of circulation show some consolidation at low levels (850mb), but weak circulation at higher levels (500mb). Despite the organized presentation on satellite, Hurricane Hunters found a generally disorganized storm this morning, with multiple potential centers. The lowest pressure that the Hunters found was 1007mb. Wind shear remains strong to the north of the storm, and this feature extends west across Puerto Rico and Hispaniola. Dry air, which has been lingering to the north of the system for the past few days, has begun to wrap around the northwest side of the storm. This, along with high wind shear along its potential track, could delay or prevent further intensification over the life of the storm. Another Hurricane Hunter mission is on its way to Emily now.


Figure 1. Visible satellite of Tropical Storm Emily at 1pm EDT.

Forecast for Tropical Storm Emily
The official forecast for Emily is a track toward the west-northwest over the next day and a half, after which it will make a turn to the northwest, and by Saturday, to the north. Although the National Hurricane Center has been shifting the forecast track to the east over the past few advisories, the U.S. coastline is still within the cone of uncertainty, and if we know something about this storm, it's that the forecast is uncertain. The CMC continues to be the western boundary of the model track forecasts, bringing Emily over Cuba and into the far eastern Gulf of Mexico. Today, on the eastern boundary of potential tracks fall the HWRF and the GFDL, which forecast Emily to cross over Hispaniola on a north-northwest trajectory, skirting the eastern edge of the Bahamas, and turning northeast before ever making connection with the U.S. coast. The Hurricane Center's official track follows the model consensus, and is the most likely track. Today, Emily is not forecast to strengthen into a hurricane within the next five days by the National Hurricane Center nor most of the models. Consensus seems to be that the storm will max out at a moderate to strong tropical cyclone, but this is assuming the storm can survive the wrath of Hispaniola.

Surviving Hispaniola

Hispaniola is somewhat notorious for being a major disruptor to tropical cyclones that dare cross over it. Since 1950, around two dozen tropical cyclones have crossed Hispaniola near where the National Hurricane Center is forecasting that Emily will pass over. A handful of these cyclones were of similar intensity with a track that was similar to Emily's forecast by various models, and although some went on to intensify (the warm Gulf of Mexico waters can be quite healing) many were fatally disrupted by the second largest island in the Caribbean.


Figure 2. Tropical cyclones that have crossed Hispaniola since 1950 (plotted using the NOAA Historical Hurricane Tracker).

Fay of 2008 developed in the Mona Passage on August 15th as a tropical storm. After a rough track westward over the length of Hispaniola, Fay emerged back into open water with little to no organized circulation, but managed to survive, and skirted the southern coast of Cuba for the next couple of days before turning north toward Florida. Many remember 2008's Fay as the storm that intensified and developed an eye-like feature over Florida after making landfall.

Cindy of 1993 was not as lucky in a battle with Hispaniola. Cindy developed as a tropical depression just east of the Lesser Antilles, and over the course of two days, tracked west-northwest through the Caribbean toward Hispaniola, strengthening into a tropical storm and reaching peak intensity just before landfall. Almost immediately upon landfall in the Dominican Republic, Tropical Storm Cindy deteriorated and the National Hurricane Center stopped issuing advisories on the system.

Emily of 1987 developed well east of the Lesser Antilles in late September and tracked northwest into the Caribbean, where it underwent a period of rapid intensification and was upgraded to a hurricane and then a major hurricane (category 3) just before landfall in the Dominican Republic. As the hurricane approached Hispaniola, it began deteriorating, and within 12 hours of landfall, Emily had weakened to a tropical storm and never regained its strength. Emily then took a turn to the northeast and tracked into the open Atlantic. Hurricane Katie of 1955 had a similar fate.

Angela

Hurricane

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An Uneasy Future for Tropical Storm Emily

By: JeffMasters, 08:48 AM GMT die 02o August, anno 2011

As of 5AM EDT, Tropical Storm Emily was located at 15.5N, 64.0W, moving W at 16 mph with sustained winds of 40 mph. It's central pressure was estimated to be 1006 mb. Satellite imagery shows that the convection around Emily's center continues to grow, with large amounts of cold anvil cirrus. However, satellite analysis of cloud-top winds suggest that Emily still has an elongated circulation, more like that of a jelly-bean than the compact circulation which is more favorable for intensification. Also, while Emily is in a low-shear region, there are large areas of wind shear to it's immediate north and south. The dry air of the Saharan Air Layer is just north of Emily, which would weaken the storm.


Figure 1 IR Satellite image of TS Emily taken at 3AM EDT August 2, 2011



Forecasting Emily
Model uncertainty is still high for forecasting Emily's track. The 00Z CMC and NOGAPS global models keep Emily on a western track, before recurving to make landfall on the western coast of Florida. The 00Z HWRF and GFDL dynamic
hurricane models both have Emily approaching the eastern coast of Florida, but recurving sharply to the northeast before making landfall. However, the premier global models, GFS and ECMWF, suggest that forecasters should be very cautious.
The 12Z ECMWF did not get a good representation of Emily in its starting conditions, so the forecast Emily did not gain strength and drifted westwards, missing Hispanola. The 00Z GFS does not have any forecast features that could be reasonably associated with Emily in my judgement. From what I can tell, the GFS moves Emily's circulation over Hispanola and Emily then never has a chance to organize. This is disconcerting since the previous 4 runs of the GFS had produced a reasonably robust tropical cyclone with winds near or just exceeding hurricane strength.

Even though the tracks produced by these models are different in their long-term outlooks, they all suggest that Emily will pass by Hispanola close enough for that island's mountains to impact the storm's winds and thus dampen any intensification. However, the 00Z NAM model does not bring Emily near the island, and keeps it moving westwards into the Caribbean sea as a well-organized storm. This, combined with the widely different solutions discussed previously, suggests that people across the Caribbean and living along the Gulf coast should keep an eye on this storm for the next several days.

I would prefer to make an intensity forecast for Emily after it has cleared the island of Hispanola and it's tall mountains. Many storms have weakened considerably after passing by there, and some have dissipated (TS Cindy in 1993, for example).

In light of this uncertainty, the NHC forecast hasn't changed that much. Emily is forecast to turn towards the northwest, making landfall somewhere in southeastern Florida on Saturday as a weak hurricane. (5AM EDT update NHC has adjusted their forecast to the east, so Emily does not make landfall in the next 5 days. Also, Emily does not reach hurricane strength in this forecast.) Tropical storm warnings have been issued for Puerto Rico and the Dominican Republic. A tropical storm watch has been issued for Haiti.


Figure 2 Official five-day track forecast for Tropical Storm Emily.

Angela will have a full post later today discussing Emily.

Thanks for reading,

Dr. Rob Carver

Updated: 09:08 AM GMT die 02o August, anno 2011

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Tropical Storm Emily forms from Invest 91L

By: JeffMasters, 12:09 AM GMT die 02o August, anno 2011

Tropical Storm Emily formed this afternoon after investigation by the Hurricane Hunters. While dodging the Lesser Antilles islands, the Hunters managed to find a closed surface circulation. Emily is currently located near 15.2°N, 62.0°W, and has maximum sustained winds of 40 mph. Thunderstorm activity has grown in size and intensity over the past 6 hours, and mid-level circulation is still elongated, but strong. The environment around Emily hasn't changed much from this morning. The moisture within the storm is still relatively high, although there continues to be a lingering dry, Saharan air mass to its north, which could become a factor in intensification. Wind shear is still high (30-40 knots) on the north side, as well.


Figure 1. Visible satellite of Tropical Storm Emily at 7:30pm EDT as it moves west into the Caribbean.

Forecast For Emily
The official track forecast is that Emily will continue to travel west-northwest through the Caribbean and cross Hispaniola Wednesday morning, after which it turns slightly more to the north for a potential landfall along the Florida east coast as a hurricane. Models continue to be split between Emily entering the Gulf of Mexico or recurving before making landfall along the East Coast. In the camp of an eastern Gulf of Mexico track are the CMC, NOGAPS, and the UKMET models. The ECMWF has been trending that way, as well. The GFS continues to favor a northwest track towards Florida before taking a turn to the northeast. The HWRF has been forecasting an eastern coast of Florida solution, and continues to do so in the 12Z run. The GFDL remains conservative and forecasts that the system will turn north and northeast well before making any connection with the U.S. coast. It is notable that although there is still much disagreement on where this system will go, but the models have been trending west in their tracks over the past few days. As the official track forecast from the National Hurricane Center illustrates, this is a U.S. landfall threat.


Figure 2. Official five-day track forecast for Tropical Storm Emily.

The National Hurricane Center forecasts that Emily will probably strengthen into a hurricane. In the 12Z runs, the GFDL brings Emily up to category 2 strength, and HWRF forecasts it to max out at category 1. DSHIPS (the SHIPS model that takes into account land interaction) forecasts maximum intensity of a moderate tropical storm. General consensus continues to be that Emily will reach a peak intensity somewhere between a moderate tropical storm and a moderate category 1 hurricane. Now that Emily has developed, and when the models ingest some data from the Hurricane Hunter missions, we will have more certainty in an intensity forecast.

Dr. Rob Carver might have an update later this evening, and I'll definitely be back tomorrow, early afternoon, with a new post on Emily.

Angela

Hurricane

Updated: 07:03 PM GMT die 09o January, anno 2012

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Invest 91L reorganizing; The heat is on (again)

By: JeffMasters, 04:16 PM GMT die 01o August, anno 2011

Invest 91L, which is located near 14°N, 57°W, is showing signs of reorganization after a pretty rough weekend. On Saturday, the wave looked ripe to develop with organized convection and the hint of a surface circulation. On Sunday a Hurricane Hunter and NOAA G9 flew into the system only to find it disorganized and negatively influenced by the burst of convection that sprouted on its western edge. Since then, low-level circulation has at least strengthened, if not consolidated, and residents of the Lesser Antilles should be prepared for tropical storm advisories to be posted on short notice. Satellite loops show decent thunderstorm activity and some mid-level circulation, and continued bursts of thunderstorms to the southwest of the invest region. The wave is surrounded by moderately strong wind shear (30-40 knots) on both the north and the south sides, which could delay development. Also, a large mass of dry, Saharan air continues to linger to 91L's north. In a mission this morning, Hurricane Hunters found winds close to tropical storm strength, but no signs of a closed surface circulation—just plenty of winds from the east or southeast. The next mission is scheduled for 2pm EDT, and they will continue every six hours if the system remains a threat.


Figure 1. Visible satellite of Invest 91L at 10:30am EDT as it moves west toward the Lesser Antilles.

Forecast For 91L
Development will probably occur in the next day or two, and the National Hurricane Center is giving the wave a 90% chance in the next 48 hours. The question now is where will it go, and how long will it remain a tropical cyclone. Models are split today, although still leaning toward an Atlantic recurving solution. In the camp of a Gulf of Mexico track are the CMC and the UKMET models. The GFS and the ECMWF are still in favor of the system tracking northwest toward Florida (and coming close) before taking a turn to the northeast. The NOGAPS model is resolving a Florida landfall in this morning's run, and the HWRF hints that it might like that solution, as well, at the end of its run. The GFDL remains conservative and forecasts that the system will turn north and northeast well before making any connection with the U.S. coast. It is notable that although there is still much disagreement on where this system will go, the models have been trending west in their tracks over the past few days. However, it is extremely difficult to nail down a track before a cyclone has even developed. Something we know for sure is that 91L is a threat to the Lesser Antilles and the Caribbean islands including Puerto Rico, Hispaniola, and the Bahamas.

In terms of intensity, both the GFDL and the HWRF are thinking this will eventually get to hurricane strength once it develops, although neither are forecasting it to become stronger than a category 1. SHIPS (which tracks 91L into the far eastern Gulf of Mexico) brings the system up to a category 1 hurricane, and the LGEM does as well, but is slower in its intensification. General consensus this morning is that 91L will max out somewhere between a moderate tropical cyclone and a moderate category 1 hurricane. Again, this is something that is difficult to predict before development itself occurs.

The Heat Is On (Again)

Someone turned the furnace on again in the central U.S., although many would argue that it was never actually turned off after the last heat wave. Heat advisories have been issued from southern Louisiana to North Dakota. Temperatures are expected to climb to 115°F in the central Plains through Wednesday, and heat index values will soar again. Oklahoma has now seen over a month of high temperatures hitting at least 100°. Some reprieve could come later this week.


Figure 2. Weather advisories issued by the National Weather Service. Heat-related advisories are pink.

Angela

Heat Hurricane

Updated: 04:18 PM GMT die 01o August, anno 2011

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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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