Area Forecast Discussion
Issued by NWS Tampa Bay Area, FL

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FXUS62 KTBW 221829
AFDTBW

Area Forecast Discussion
National Weather Service Tampa Bay Ruskin FL
229 PM EDT Mon May 22 2017

.SYNOPSIS...
18Z water vapor and H4 RAP analysis shows an amplified
upper level pattern in place over the CONUS...anchored by a
large closed upper low spinning over the upper midwest.
Several impulses are rounding is larger circulation. One
weak shortwave passed through our region last night and was
the forcing mechanism for the showers in the pre-dawn hours.
This energy has no passed by...and the shower activity has
dissipated. Another stronger impulse can be seen dropping
southward into the high plains. This shortwave is destined
to have a much greater impact on our weather during the mid-
week period as it amplifies southward and moves across the
northern Gulf of Mexico. We will talk more about this
further down this discussion.

At the surface...Atlantic high pressure ridges westward
across the Florida peninsula...but is starting to shift
southward toward the Florida straits. Low level synoptic
winds which have been out of the east/SE the past several
days are shifting to the south as this ridge axis
moves...and eventually will veer to the southwest by
Tuesday.

&&

.SHORT TERM (Rest of today through Tuesday)...
Without the easterly flow to hold the sea- breeze
back...expect this boundary to move steadily inland with
time...making it well past the I-75 corridor by late
afternoon. Due to this change from previous days...higher
rain chances for diurnal storms will be well inland as well.
Close to the coast...storms are unlikely later today. The
main sea-breeze collision looks to take place across the
central portion of the peninsula
(Polk/Highlands/DeSoto/Hardee/Sumter counties). Storms are
likely to continue in eastern Polk/Highlands counties a few
hours past sunset before finally quieting down for the
night.

Tuesday is going to be the transition day between sea-breeze
dominated weather today...and widespread synoptic/frontal
rain Wednesday into Thursday. Synoptic winds will be out of
the southwest by Tuesday...keeping any sea-breeze
unorganized and pushed well inland and out of our area
before much potential for convection occurs. Off to our
northwest...the pre-mentioned trough will be amplifying
across the central part of the country...with upper flow
becoming cyclonic in nature all the way to the southeast
coast. With little in the way of sea-breeze storms...most of
the area will be dry (in terms of rain) Tuesday...but the
flow off the Gulf will keep all of us quite humid...under
considerable high level cirrus to dim the sun (especially
along and north of the I-4 corridor). Although most of us
are going to see a dry day...the potential for some
synoptic forced showers to begin impacting our far northern
areas (Mainly north of Brooksville) off the Gulf is
increasing. GFS/ECMWF both show a highly diffluent flow
developing aloft over the FL Big Bend area by Tuesday
afternoon, and these solutions suggest this forcing will be
enough to support at least SCT activity. The NAM is a bit
slower with this forcing to arrive, but this model often has
a slow bias toward frontal precipitation, and will lean
toward the faster solutions. All guidance agrees on more
widespread activity becoming likely over our Nature Coast
zones during Tuesday Night.

&&

.Mid/Long Term (Tuesday Night - Sunday)...
A significant trough amplification for late May takes place into the
northern Gulf late Tuesday Night through Wednesday. Increasing large
scale ascent ahead of this trough...supplemented by diffluent flow
aloft is quite favorable to support widespread heavy rainfall across
the Florida peninsula. Associated surface front will be slow to
advance across the region, and this sets up the potential for
several rounds of much needed rainfall to move across the region. At
the present time, we are likely looking at a widespread 2-4 inch
rain event across the area with isolated higher amounts likely. In
addition to the heavy rainfall, increasing wind fields/deep layer
shear (35-45kts) ahead of the trough is plenty to support more
organized thunderstorm/updraft potential. The storm prediction
center has outlooked our entire region in a slight risk of severe
weather (including isolated tornadoes) Wednesday/Wednesday
night...and feel this is appropriate given the NWP ensemble
solutions for this event. The most organized severe weather
potential looks to be Wednesday evening through early Thursday
morning with greatest severe parameters coincide with each other.
Still a little but more time to narrow down specifics in regard to
timing and the severe potential but nevertheless Wednesday will
certainly be a wet day across west-central and SW Florida so plan
accordingly.

Precip will linger across the area to start the day on Thursday
before the front very slowly moves south of our area by the late
afternoon. Gradually clearing skies, from north to south, can be
expected with slightly drier air infiltrating the area behind the
front especially from the Bay Area north. This will be short-lived
however given the time of year and we will begin to see moisture
increase on Friday through the weekend. A return to near seasonal
temps can be expected by Friday into the weekend with low end
shower/isolated storm chances returning mainly across our southern
and interior zones

&&

.AVIATION...
VFR conditions will prevail early this afternoon. Sea-
breeze will quickly move inland past all terminals this
afternoon...shifting winds to the southwest. Best potential
for storms later this afternoon will be well inland. Storms
may form in the vicinity of KLAL, but then likely will move
further east by the evening hours. General VFR conditions
continue overnight into Tuesday morning with a light south
to southeast flow.

&&

.MARINE...
High pressure ridge axis will slowly move south early this
week to the Florida Straits...with winds veering to the
southwest. Winds increase to near cautionary levels tonight
into Tuesday...and then may approach advisory levels ahead
of an approaching cold front Wednesday into Wednesday night.
This front will pass south of the region during Thursday and
be followed by high pressure for the end of the week.
Numerous to widespread showers and thunderstorms...some on
the strong side are anticipated across the coastal waters
Tuesday night into Thursday. Boaters are urged to check the
latest forecasts with respect to these storms.

&&

.FIRE WEATHER...
No significant fire weather concerns are anticipated through
Tuesday as relative humidity values generally remain above
35 percent. A widespread wetting rainfall is expected to
accompany a frontal passage beginning Tuesday night over the
northern peninsula...and continuing for all areas Wednesday
and Wednesday night. Drier air will arrive behind this front
for the end of the week.

Fog Potential...No significant fog concerns are anticipated
through the next several days.

&&

.Preliminary Point Temps/PoPs...
TPA  75  87  77  83 /   0  10  40  70
FMY  73  90  75  89 /  10  10  10  50
GIF  72  90  74  85 /  40  20  20  50
SRQ  75  86  77  84 /  10  10  30  70
BKV  71  87  71  83 /   0  20  50  70
SPG  76  86  76  84 /  10  10  40  70

&&

.TBW WATCHES/WARNINGS/ADVISORIES...
FL...None.
Gulf waters...None.

&&

$$

SYNOPSIS/SHORT TERM/AVIATION/MARINE/FIRE WX...Mroczka
MID TERM/LONG TERM/DECISION SUPPORT...McKaughan



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