Funnel Cloud in Florida, September 18, 2023

Area Forecast Discussion
National Weather Service Tampa Bay Ruskin FL
908 AM EDT Mon Sep 18 2023

...New UPDATE...

.UPDATE...
Issued at 843 AM EDT Mon Sep 18 2023

There is quite a PWAT gradient in place this morning across the
region with values as low as 0.5" in the northern portions of the
state and values as high as 1.8-2" in central/southern portions
of the peninsula as a cold front continues to slowly push
southward. South of the cold front, coastal areas from Tampa Bay
southward have been dealing with scattered showers and occasional
storms moving onshore so far today with this activity generally
expected to push inland and mainly become more focused to areas
south of I-4 where sea breeze interactions and deeper moisture
will support scattered to numerous showers and thunderstorms later
today. Meanwhile, drier air will continue to advect in from the
north and as a result, there will be a notable difference in
humidity levels across the Nature Coast today with a rather
pleasant day ahead with dewpoints in the low/mid 60s, though more
humid conditions continue to linger in central/southern FL as
dewpoints remain in the low/mid 70s.

&&

.DISCUSSION...
Issued at 455 AM EDT Mon Sep 18 2023

Longwave trough axis over the E CONUS this morning with W/SW flow
aloft overspreading the region, while a shortwave rounding its
base and associated surface low approaching the E Seaboard have
allowed a cold front to push into the northern peninsula and
Nature Coast. Shortwave pulls away to the NE into Tuesday causing
the front to stall over central/south FL and linger through the
week as flow aloft becomes parallel to the boundary. Broad
troughing aloft remains over the region through the week before
ridging builds upstream from the Central Plains into SE Canada,
cutting off the trough from the main flow with a closed low aloft
forming over the SE U.S around the Thursday/Friday timeframe.
Guidance then depicts an area of low pressure forming at the
surface along the remnant boundary near the SE U.S. coast in
response, lifting generally N/NW across the GA/Carolinas coast
and into the Mid Atlantic during the weekend as ridging builds
over the W Atlantic and into FL into early next week.

For today, expect showers with a few storms moving ashore early
across most of W FL as the front presses south, with activity
shifting southward through the morning into afternoon with
progression of the front. Drier air works its way into northern
areas and eventually down to around the I-4 corridor with
diminishing rain chances through the day, while SWFL and southern
interior areas to the south will continue to see scattered showers
and thunderstorms through the afternoon and into evening. Similar
conditions expected on Tuesday after the front stalls over the
southern half of the peninsula, with the boundary bisecting drier
conditions to the north and more humid conditions with scattered
showers/storms southward. Boundary lingers through the week with
moisture and rain chances gradually creeping back northward before
late week SE U.S. low development sprinkles a bit of uncertainty
into the forecast. Northerly flow on the western fringe of the
low would allow for another push of drier air into the peninsula
next weekend per current guidance indications, however, forecast
adjustments remain likely through the week to reflect latest
guidance trends and observations.

&&

.AVIATION...
(12Z TAFS)
Issued at 742 AM EDT Mon Sep 18 2023

Scattered showers moving onshore from the Gulf this morning may
move near terminals occasionally so brief periods of MVFR
restrictions could occur at times. Otherwise, VFR conditions
should prevail for Tampa Bay area terminals later today as a cold
front brings drier air across central FL, but VCTS has been
added at KPGD/KFMY/KRSW where the sea breeze combined with deeper
moisture will support showers and thunderstorms this afternoon
and evening. Winds then shift to the ENE tonight in the wake of
the cold front with some low CIGs possible across southwest FL
overnight as low level moisture lingers.

&&

.MARINE...
Issued at 455 AM EDT Mon Sep 18 2023

Winds becoming northerly over the waters today as a cold front
moves south across waters before stalling over or near the
southern waters into Tuesday. Winds shift out of the northeast on
Tuesday as high pressure builds over the waters from the north,
and remain east to northeast into late week. No headlines
currently although winds may approach cautionary levels late in
the week as the gradient tightens in response to an area of low
pressure developing over the western Atlantic.

&&

.FIRE WEATHER...
Issued at 455 AM EDT Mon Sep 18 2023

A cold front moves across the northern and central peninsula today
followed by a drier air mass filtering into the Nature Coast down to
around I-4 this afternoon into Tuesday as high pressure builds from
the north. Afternoon minimum RHs drop below 50 percent today and
Tuesday across those areas but are expected to remain above critical
levels before moisture recovers around mid week, with areas south of
I-4 and the frontal boundary remaining well above critical levels.
Expect northerly winds today, shifting to northeasterly on Tuesday
and persisting through late week.

&&

.PRELIMINARY POINT TEMPS/POPS...
TPA  91  76  91  75 /  30  10  30  20
FMY  92  75  89  75 /  80  40  80  40
GIF  90  72  89  72 /  40  20  30  20
SRQ  92  74  91  73 /  40  20  50  40
BKV  91  68  92  69 /  20   0  10  20
SPG  89  78  89  77 /  30  10  30  30

&&

Sea Breeze Thunderstorm Regime For Monday: 4
Sea Breeze Thunderstorm Regime For Tuesday: 2

For additional information on sea breeze regimes, go to:
     https://www.weather.gov/tbw/ThunderstormClimatology

&&

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

&&

UPDATE/AVIATION...Giarratana
MARINE/FIRE WEATHER...Hurt
DECISION SUPPORT...Wynn
UPPER AIR/CLIMATE...Wynn