Area Forecast Discussion
Issued by NWS Tampa Bay Area, FL

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FXUS62 KTBW 222121
AFDTBW

Area Forecast Discussion
National Weather Service Tampa Bay Ruskin FL
521 PM EDT Tue Aug 22 2017

.UPDATE...
Although some moisture return is evident in WV imagery
aloft over the southern half of the forecast area, the
extent of influx has been minimal. In addition...it is quite
evident via satellite trends (and looking out the
window)...the we are still dealing with efficient
suppression in the atmosphere...keeping the cu fields
generally shallow. Another big factor we are seeing as of
5PM is the we still have fairly healthy offshore flow along
the Suncoast...making the likelihood of defined sea-breeze
formation increasingly less likely within the next hour or
two. With all this in mind...have made a fairly large
decrease in the overall rain chances for our far southern
zones from Highlands to Charlotte/Lee Counties. Further
north than that, not needing much in the way of change as
chances were already slight chance/isolated at best up to
the I-4 corridor...and less than 10% further north.

Will not remove PoPs altogether this evening for the
southern zones, as still anticipate a few widely scattered
cells to get established between 22Z and 00Z...mainly south
of a line from Sarasota to Sebring...with better chances
the further south. However, at this point...all the factors
above make it difficult to expect more than about a 30%
chance at any one location. Will remove all PoPs over the
landmass after 02Z...with a dry rest of the overnight
region-wide.

The moisture will continue a slow recovery aloft during the
day Wednesday...and be back above normal for all areas by
Thursday. The combination of this increase in available
moisture, and the arrival of a weak surface trough from the
east (and resulting enhanced surface focus)...the chances
for diurnal showers and storms will slowly ramp up through
the middle of the week.

.Aviation (23/00Z through 24/00Z)...
Prevailing VFR conditions expected for all terminals through
the TAF period...outside of a brief passing shower or storm.
Only a slight chance of a passing storm for KPGD/KFMY/KRSW
through 02Z this evening...and very unlikely further north.
Isolated to widely scattered late afternoon storms return
to the I-4 corridor terminals Thursday afternoon, with
potential for a bit higher storm coverage southward to the
Fort Myers region.

&&

.Prev Discussion... /issued 303 PM EDT Tue Aug 22 2017/

SHORT TERM (Tonight-Wednesday)...
A tropical wave just to the east of the southeast FL coast
will gradually shift west over south FL and weaken across
the area through Wednesday. Deep moisture will move into the
area and allow for scattered to numerous showers and
thunderstorms, with the highest chances Wednesday afternoon
and across the south. Generally east to NE winds will be in
place through the period, becoming light overnight, and a
weak sea breeze Wednesday afternoon turning winds onshore.
Lows tonight will be in the lower to mid 70s north and
inland, and in the upper 70s to lower 80s along the coast.
Highs Wednesday in the lower to mid 90s.

LONG TERM (Wednesday Night through Next Tuesday)...
At the beginning of the long range period, a potent upper
trough will extend from the Northern Plains into New
England. High pressure will dominate the remainder of the
country with a couple of noted weaknesses in the tropics. At
the surface, high pressure will extend across the western
Atlantic Ocean and the Gulf of Mexico with a weak tropical
low near the southern tip of Florida, and a strengthening
low pressure system over the western Gulf of Mexico.

We again face an uncertain forecast as models continue to
handle the evolution of a weak surface low quite poorly.
This tropical disturbance is currently situated over the
Bahamas and will drift slowly west to northwest to a
position either over the southern Florida peninsula or just
offshore in the far eastern Gulf by late Wednesday. As is
common with weak areas of low pressure, medium range
guidance can hardly resolve the system, which is making the
exact track of the feature very difficult to discern. The
more reliable mid/long range solutions are beginning to
converge somewhat, but we have a long way to go before
consensus is obtained. To complicate things, the remnants of
Harvey look to move out into the western Gulf, eventually
strengthening into at least a tropical depression or
tropical storm. Both of these features, along with a
deepening of the upper trough and a southward moving cold
front will lead to a complicated forecast and error is
certain to be quite high as we move beyond this weekend.

What we do know is that the weak tropical disturbance is
likely to at least affect areas of southern and perhaps
central Florida Wednesday into the weekend, as a plume of
deep tropical moisture joins the daily seabreeze
circulations and daytime heating. This should promote fairly
widespread showers and thunderstorms Thursday through
Saturday afternoon, especially south of the I-4 corridor.
Localized flooding may occur in areas that receive training
rounds of heavy rain, though widespread flooding doesn`t
appear likely at this time. Further north, over north
central Florida and along the Nature Coast, lesser chances
of rain will exist due in part to the presence of some
slightly drier air aloft.

Beyond the weekend, even greater uncertainty exists as
models attempt to spin up two tropical cyclones along the
stalled frontal boundary. Right now, we look to remain
between these two systems, which would generally favor drier
and hotter conditions that normal, but a small deviation
could result in greater impacts to the area, and will will
have to monitor the situation closely.

MARINE...
Weak pressures will be in place across the waters with weak
ridging in place and a tropical wave along the SE FL coast.
Increasing moisture will allow for scattered to numerous
showers and thunderstorms through the weekend as generally
easterly flow continues, turning onshore along the coast
each afternoon. No headlines currently expected through the
period.

FIRE WEATHER...
No concerns.

&&

.Preliminary Point Temps/PoPs...
TPA  79  94  79  91 /  10  40  30  60
FMY  77  92  76  89 /  30  70  40  80
GIF  76  94  76  92 /  10  50  20  70
SRQ  77  94  78  90 /  10  40  30  60
BKV  73  95  75  93 /  10  30  20  60
SPG  80  94  79  90 /  10  30  30  60

&&

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

$$

UPDATE/AVIATION...Mroczka
PREVIOUS DISCUSSION...HUBBARD/AUSTIN



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