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Area forecast discussion
National Weather Service Tampa Bay Ruskin Florida
334 am EST Wed Dec 12 2018

Short term (today - thursday)...
skies are nearly clear with just a few wisps of very thin
cirrus here and there. Where winds have gone calm,
temperatures are running in the middle 30s. Much of the area
has continued to see the northeasterly drainage wind, which
is preventing the decoupling of the atmosphere and allowing
warmer temperatures aloft to mix down to the surface. We've
seen temperatures go from the lower 40s, down to 33
degrees, then back to the lower 40s again in the course of
an hour! We still have several hours to go before sunrise,
so no changes planned to the frost advisory. It may well end
up only an issue for areas well protected from the wind.
Even parts of Pinellas County have briefly reached the upper
30s overnight.

Any frost that does occur will quickly melt after 7 am as the sun
GOES to work. There will be a fair amount of high clouds moving
across the sky later today, which may dim the sun from time to time.
Temperatures will continue on the cool side, ranging from the lower
60s north to near 70 south.

High pressure will reach the mid-Atlantic coast tonight providing a
general light east to northeast flow and increasing moisture. Skies
should gradually become partly to mostly cloudy, which will keep
temperatures warmer than they were last night.

By Thursday, a vigorous upper-level trough and closed low will be
pushing eastward across Texas. Southeasterly winds will begin to
increase, especially over the Gulf waters as the pressure gradient
tightens between the departing ridge of high pressure and the
approaching Gulf Coast system. Any shower activity should be
confined mainly to the eastern half of the state, but we can't rule
out a few showers in our interior counties. Even with more cloud
cover, temperatures will rebound into the lower to middle 70s.

Long term (thursday night - tuesday)...
once again we will be dealing with a potent system that models just
can't seem to come to terms with. The Canadian and GFS are faster
bringing the main area of showers and thunderstorms to our coastline
late Thursday night or early Friday. The European model (ecmwf) and NAM are slower,
with the main impacts occurring Friday into Friday night. The GFS is
trending slower, so we while the forecast will still show showers
and storms beginning Thursday night, it will also show rain chances
lingering all the way into part of Saturday.

As far as severe threat GOES, it appears to be most likely near and
north of the I-4 corridor. Keep in mind that we are still 2+ days
out, so things will change.

Based on just the gfs: the 925mb southerly jet is approaching the
Nature Coast very early Friday morning, but the best low-level jet
dynamics appear to be lifting north of our area around 7 am Friday,
with speeds up to 60 knots.

Based on just the ecmwf: a 925mb southerly jet of 50 to 55
knots approaches the Nature Coast around 1 PM Friday. So for this
model, that would be the most likely onset of the heavier
thunderstorms.

While we do think a marginal to slight severe weather risk will
materialize, it's really too early to pinpoint where and exactly
when it will occur due to the complex nature of this large
storm system.

Another issue will be the likelihood of hazardous surf and rip
currents. When this system is moving across the northwest Gulf Coast
states, it will be producing westerly winds up to gale force across
the northern Gulf Thursday night and Friday. The winds will begin to
diminish as the westerlies approach Florida, but large swells will
be inbound and likely begin to affect our coast Friday night and
especially on Saturday. Combined swell and wind wave could easily
reach 8 to 10 feet, and these large waves will generate dangerous
rip currents and surf through Saturday night, with some improvement
during Sunday.

As for the rest of the forecast period, skies should clear Saturday
night as the cold front moves well east of the region. By Sunday,
cooler and drier air will have moved in. This airmass will not be as
cold as the previous one, but we may see a stretch of mid 40s to mid
50s at night and upper 60s to lower 70s each day through at least
Tuesday.

&&

Aviation...
VFR conditions to prevail through the period with mostly clear
skies and light north-northeast winds less than 10 knots. No
other aviation impacts expected.

&&

Marine...
a significant wave event is becoming more likely for the end of this
week. A storm system will move across the northern Gulf Coast states
and produce westerly winds to near gale force. This will create
large waves which will move eastward across the Gulf and toward the
Florida Peninsula late Friday or Friday night. At the same time, the
storm system will be bringing onshore winds of at least 20 knots
along with numerous showers and storms. Mariners are urged to check
forecasts regularly before heading out for this weekend. Combined
seas will likely be in the 8 to 10 foot range. The seas will
begin to subside on Sunday.

&&

Fire weather...
no significant fire weather issues expected through the rest of this
week. We may see portions of the Nature Coast reach 35 percent
relative humidity this afternoon, but it will not be coupled with
strong winds and erc values are forecast to remain low to
moderate.

&&

Preliminary point temps/pops...
tpa 66 52 73 64 / 0 0 10 60
fmy 72 56 78 66 / 0 10 10 30
gif 67 52 74 63 / 0 10 20 40
srq 68 54 76 66 / 0 0 10 50
bkv 65 45 74 64 / 0 0 10 60
spg 64 56 72 64 / 0 0 10 60

&&

Tbw watches/warnings/advisories...
Florida...frost advisory until 8 am EST this morning for coastal
Levy-inland Citrus-inland Hernando-inland Levy-Sumter.

Gulf waters...none.

&&

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