Australia Braces for Debbie; Localized Tornado Outbreak Possible Sunday in TX/OK

By Jeff Masters and Bob Henson
Published: 05:17 PM GMT die 26o March, anno 2017

Northeast Australia’s Queensland coast is bracing for the arrival of Tropical Cyclone Debbie, which intensified into a Category 1 storm with 80 mph winds on Sunday morning. Debbie is headed west-southwest at about 4 mph, and is expected to make landfall on Tuesday morning local time (Monday evening in the U.S.) The storm has quite favorable conditions for intensification, with light wind shear and warm ocean temperatures of 29 - 30°C (84 - 86°F.) However, satellite images on Sunday morning showed that Debbie had failed to take full advantage of these favorable conditions for intensification, thanks to dry air pulled off the coast of Australia that had wrapped into the core of the storm. There is still time for Debbie to undergo a period of rapid intensification before landfall, and the storm could well be at Category 3 strength by then, as predicted by the Joint Typhoon Warning Center.

According to Australian hurricane expert Bruce Harper, the population of the area expected to receive the brunt of Debbie’s winds is around 15,000. The region is surrounded by flat sugar cane fields, and heavy rains from the storm will likely cause considerable agricultural damage. Debbie is a very moist storm, and a large area of torrential rain in excess of 8 inches will accompany the storm as it make landfall, according to the 06 UTC Sunday run of the HWRF model. A maximum storm surge of about 3 meters (10 feet) and storm tide (height of the surge plus the tide) of about 4 meters (13 feet) can be expected to the left of where the center makes landfall, if Debbie intensifies to Category 3 strength.

Figure 1. Tropical Cyclone Debbie, as seen on Sunday afternoon (local time) March 26, 2017. Image credit: NASA Worldview.

Tropical cyclone history of the Queensland, Australia coast
According to NOAA’s historical Hurricane Tracks tool, Queensland has been hit by nine tropical cyclones of Category 3 or higher strength on the Saffir-Simpson Scale since 1989. Four of these storms have hit since 2011:

Tropical Cyclone Marcia hit central Queensland near Shoalwater Bay as a Category 4 storm with 145 mph winds on February 20, 2015, causing $590 million in damage. No fatalities were reported.

Tropical Cyclone Nathan hit far northern Queensland as a Category 3 storm with 115 mph winds on March 19, 2015, causing $57 million in damage.

Tropical Cyclone Ita hit Cape Flattery, Queensland as a Category 4 storm with 145 mph winds on April 12, 2014, causing over $1 billion in damage to agriculture. Ita killed 40 people in the Solomon Islands while it was forming (thanks go to WU member elioe for this correction.)

Queensland suffered a devastating blow on February 3, 2011, when Tropical Cyclone Yasi made landfall in northern Queensland as a Category 4 storm with 155 mph winds, killing 1 and causing $2.5 billion in damage (2011 dollars.) According to EM-DAT, Yasi was the most damaging tropical cyclone in Australian history.

The Australian Bureau of Meteorology has a nice summary of the major to storms to impact Queensland before 2011.

An early appearance of the Atlantic’s first named storm of 2017 unlikely this week
A large area of low pressure has formed a few hundred miles east of the Bahamas over waters that are near 24°C (75°F)—barely warm enough to support formation of a subtropical depression or subtropical storm. Satellite loops on Sunday morning showed that the low had little in the way of organized heavy thunderstorm activity, and with wind shear a very high 50 - 60 knots, development of this storm into a subtropical storm is unlikely. The low will head north and then northeast, passing a few hundred miles southeast of Bermuda on Tuesday. According to NOAA’s Historical Hurricane Tracks, the only March tropical cyclone ever recorded in the Atlantic was a Category 2 hurricane that passed through the Lesser Antilles on March 8, 1908.

Figure 2. At the center of a compact severe weather threat area highlighted by the NOAA/NWS Storm Prediction Center for Sunday, March 27, as of 11:30 am CDT was a moderate risk across parts of south-central Oklahoma and far north Texas (red). “Moderate” is the second-highest of the risk ratings issued by SPC.

Localized severe weather outbreak expected on Sunday in OK/TX
A couple of intense supercells, possibly bearing tornadoes, may crop up late Sunday in south central Oklahoma, possibly extending into north central Texas. Low-level moisture was quite limited across the area late Sunday morning, with dewpoints mainly between 50°F and 55°F. However, dewpoints in the low- to mid-60s had surged from the Gulf of Mexico to just south of the Dallas-Fort Worth area. As a compact upper-level low swings into the Southern Plains, a surface low centered near the Oklahoma Panhandle on Sunday morning will quickly strengthen, with a sharp dryline and cold front extending southward.

Figure 3. A midlatitude storm wrapping up over the Southern Plains is arriving hard on the heels of another midlatitude storm now centered in northern Illinois, as shown here in a NOAA GOES-16 visible image from 10:52 am CDT Sunday, March 27, 2017. The short distance between these systems has made it difficult for moisture from the Gulf of Mexico to return in time for today’s potential severe weather in OK/TX. Data from GOES-16 are preliminary, undergoing testing, and have not yet been declared operational. Image credit: College of DuPage.

Moisture streaming northward from the Gulf is not quite as deep as it can be this time of year, but it appears richer than it did with Friday’s limited severe weather. If deep moisture does make its way as far north as the corridor between DFW and Oklahoma City, conditions there will be quite favorable for tornadic storms, with substantial instability (perhaps up to 2000 joules per kilogram of CAPE) and ample wind shear (winds will be veering as well as strengthening with height). Although low-level wind shear will not be exceptionally strong, the distinct veering (turning of winds with height) should help lead to well-structured supercells. I wouldn’t expect a widespread tornado outbreak, but the situation definitely bears watching in and near the Interstate 35 corridor between DFW and OKC, especially between about 4:00 and 9:00 pm CDT Sunday.

The NOAA/NWS Storm Prediction Center raised the risk level in this area from enhanced to moderate early Sunday morning, highlighting the chance of tornadoes, significant large hail (larger than 2” in diameter) and very high wind (gusts of at least 74 mph). Short-range computer models indicate that the storms may congeal into a squall line on Sunday from eastern Oklahoma into western Arkansas. Thunderstorms should be somewhat less severe but more widespread across northern Oklahoma and much of Kansas.

We’ll be back on Monday with an update on Debbie and on more possibilities of U.S. severe weather in the upcoming week.

Jeff Masters (tropical) and Bob Henson (severe)

Figure 4. Dewpoint changes between 8:00 and 11:00 am CDT Sunday, March 26, 2017 (increases in green, decreases in tan) atop surface winds at 11:00 am. Dewpoints increased more than 12°F in three hours across parts of north Texas as a surge of moisture arrived from the Gulf of Mexico. Image credit: NOAA/NWS Storm Prediction Center.

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About The Author
Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather

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