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Area Forecast Discussion (AFD)

Issued by Tampa Bay Area, FL (TBW)

FXUS62 KTBW 150810

Area Forecast Discussion
National Weather Service Tampa Bay Ruskin FL
410 AM EDT Sun Sep 15 2019

08z water vapor and H4 RAP analysis shows the Florida peninsula
within a complex upper level pattern between Tropical Storm
Humberto to our east and a large cyclonic gyre / upper low
spinning over the central Gulf of Mexico. The two entities are not
entire separated with a broad trough extending between the two
over the Florida peninsula. Northern stream flow is displaced 
well to our north and currently disconnected from either of these 
two systems. 

At the surface, our region resides in a broad north/northeast flow
pattern partly related to the circulation around Humberto and an
inverted trough over the central Gulf, underneath the parent upper
low. This pattern will be breaking down through the day as
Humberto continues to shift northward and the upper low and
surface reflection shift westward. 


.SHORT TERM (Today through Monday)...
A generally quiet morning weather-wise is in the forecast, other
than a few possible isolated showers migrating within the 
moist easterly low level flow into Sumter/Polk counties. By this
afternoon, look for the flow over north/central Florida to remain
out of the north around the Humberto circulation, while south
Florida sees its flow shift back to a westerly part
of the inflow into the southern flank of Humberto. This change in
wind direction will set up a decent low level convergence zone
roughly along the I-4 corridor and off a bit to the south. The
focus for ascent within this zone will force a scattering of
showers and storms during the afternoon hours, and it is in this
I-4 corridor down through Highlands/Hardee/DeSoto/Sarasota/Manatee
counties where rain chances look to be highest the second half of
the day. This activity persists into the early evening...but 
should rapidly diminish with the setting of the sun and loss of 
diurnal insolation. 

The first in a series of drier air intrusions rotating down the
backside of Humberto during the upcoming week will arrive during
Monday. This drier air looks to keep the forecast mainly rain free
for much of the area. The only real residual moisture left to
support diurnal showers looks to reside over inland areas...mainly
eastern Polk/Highlands counties. Can not rule out a brief shower
further west, but the chances appear low enough to keep out of the
forecast at this time. While the atmosphere will not be abnormally
dry on Monday, there will certainly be a decrease in PWATS from
what will be over the region today. More pronounced drying of the
atmospheric column will come with the next surge of dry air
arriving for Tuesday.

.LONG TERM (Tuesday through Saturday)...
The middle and end of the week will see a series of changeable
conditions day-by-day. A fairly significant surge of drier column
air will arrive from the north on Tuesday, dropping PWATS almost 
region- wide down to 1.5" or less. With the drier air in place, 
the forecast looks rather benign with very low rain chances and 
near normal temps. By Wednesday, global models are in good
agreement that we will see a pseudo "backdoor" frontal system
pushing through the region from northeast to southwest. Moisture
pooling ahead of this front should be enough to force a few
scattered showers during the second half of the day. Quickly in
the wake of this front, another dry intrusion will overspread the
region dropping rain chances back down for the end of the work
week. The greatest impact of this frontal system will be some
"lower" dewpoints. I say lower based on what we have seen for the
past few months. MOS numbers are showing dewpoints dropping into
the 60s by Thursday, which should actually feel pretty good. The
other significant impact will be some rather rough boating
conditions over the eastern Gulf of Mexico. Northeasterly winds
are likely to approach advisory levels with some rather rough
seas. Boaters planning to go out during the end of the week should
keep tabs on the latest forecasts. 


.AVIATION (15/08Z through 16/06Z)... Earlier convection near 
KFMY/KRSW has subsided allowing for prevailing VFR conditions 
under a high level canopy early this morning. Some small potential
for MVFR BR at KFMY/KRSW toward dawn, especially if higher cirrus
can thin, but for now keeping out of current forecast. Sunday 
will feature mainly VFR conditions with developing sct TSRA after 
17/18Z for all terminals. Sct storms diminish quickly with sunset 
this evening. 


Gusty northeasterly winds this morning will occasionally reach
cautionary levels to the north of Englewood, but are expected
to lessen through the day while shifting out of the north and
northwest. High pressure builds over the region for the early portion
of the week with generally light winds and seas. A front is then
expected to push through the region Wednesday night. Elevated
northeasterly winds up to 20 knots and rough seas as then expected to
persist over the eastern Gulf of Mexico for Thursday and Friday. 


A scattering of showers and storms will develop during the early
afternoon before dissipating this evening. A series of drier air
intrusions are expected to progress south into the region during
the early and middle portion of the week, however, relative 
humidity is still expected to remain above critical levels and no
significant fire weather concerns are anticipated. 

Fog Potential...No significant fog is expected.


.Preliminary Point Temps/PoPs...
TPA  91  77  91  77 /  60  20  10  10 
FMY  91  77  91  76 /  30  20  20  10 
GIF  92  75  93  74 /  60  20  20  10 
SRQ  91  77  91  77 /  50  20  10  10 
BKV  92  74  92  74 /  50  10  10  10 
SPG  91  77  91  77 /  60  20  10  10 


Gulf waters...None.