Severe Thunderstorm Warning 537, NWS Tallahassee, FL

Area Forecast Discussion
National Weather Service Tallahassee FL
350 PM EDT Fri Aug 11 2023

...New SYNOPSIS, NEAR TERM, SHORT TERM, LONG TERM, AVIATION,
MARINE, FIRE WEATHER, HYDROLOGY...

...EXCESSIVE HEAT WILL STRENGTHEN ITS GRIP THIS WEEKEND...

.NEAR TERM...
(Through Saturday)
Issued at 349 PM EDT Fri Aug 11 2023

A cluster of severe thunderstorms is now rolling south-southeast
through east-central Alabama. It will continue into our southeast
Alabama and southwest Georgia counties over the next few hours,
before weakening upon approach to the Florida state line early
this evening. A few damaging wind gusts will be the main concern,
given strong instability and high Downdraft CAPE of 1100-1400 J/kg in
the pre- storm environment. Effective bulk shear near 20 knots is
respectable by August standards, especially given the strong
instability.

500 mb heights will rise 10-20 meters on Saturday, compared with
today, as the big 500 mb heat wave high along the western Gulf
Coast strengthens and expands in this direction. As a result,
Saturday should be at least as hot as today, if not a degree or so
hotter. Have upgraded Saturdays Excessive Heat Watch to a Warning,
where heat index values are forecast to reach or exceed 113
degrees. Given the high confidence in even hotter heat index
values for Sunday, have issued an Excessive Heat Watch with a bit
more lead time than usual.

Otherwise, northwest and northerly mid-level flow will be weaker
on Saturday than today. This will lessen the risk of organized
clusters of storms rolling our of central Alabama and Georgia, but
seabreeze-driven thunderstorms will still be going strong in the
afternoon over our Florida and far south Georgia counties.

&&

.SHORT TERM...
(Saturday night through Sunday night)
Issued at 349 PM EDT Fri Aug 11 2023

On Sunday, mid-level westerlies lift north of the region as high
pressure ridges in aloft. Light 850 hPa west/northwest flow will
impede the inland progress of the seabreeze, which should again
delay convective initiation. With ridging aloft, 500 hPa heights are
modeled around 594 Decameters. As such, another hot and humid day is
on tap with limited mixing. The record high in Tallahassee on Sunday
is 100F set in 1999 and our forecast high of 100F high would tie
that record. The combination of heat and humidity is forecast to
lead to dangerously high heat index/apparent temperature values,
with the potential for heat advisory (108-112F) and/or Excessive
Heat Warning (AOA 113F) criteria. PoPs on Sunday will be slightly
below climo on the 30-40 pct range. We've included an area around 50
pct northwest of the Flint River in GA into Southeast AL, where some
storms may move in from the northwest, in addition to limited
seabreeze convection elsewhere. Of note is the winds aloft weaken on
Sunday with the aforementioned ridging, so any stronger storms will
be pulse-type, although even wind gust potential may be more limited
due to meager downburst potential.

&&

.LONG TERM...
(Monday through Thursday)
Issued at 349 PM EDT Fri Aug 11 2023

Mid-level ridging begins to breakdown on Monday with seabreeze-
forced convection supporting PoPs of 30-40 pct. A front will
approach from the northwest on Tuesday, with PoPs increasing to
around 50 pct. Once again, dangerously high heat index/apparent
temperature values are forecast to continue on Monday and Tuesday,
with the potential for heat advisory (108-112F) and/or Excessive
Heat Warning (AOA 113F) criteria. As the aforementioned front
stalls and undergoes frontolysis across the region from mid to
late week, PoPs will increase above climo (~50%) between Wednesday
and Friday, especially in the FL Big Bend. Ensembles indicate a
gradient in moisture across the region (drier NW, wetter SE),
so there is uncertainty in the PoP forecast. With falling heights
aloft, increased cloud cover/precip, and perhaps lower dew points,
heat index/apparent temperatures should return to more sane values.

&&

.AVIATION...
(18Z TAFS)
Issued at 349 PM EDT Fri Aug 11 2023

Seabreeze-driven thunderstorms are still affecting the vicinity of
TLH. A more organized round of thunderstorms is now rolling
southeast past Columbus GA and Eufaula AL. It will continue to
move southeast over the next few hours, blowing past DHN and ABY
first. It could eventually passing ECP, VLD, and TLH early this
evening, but the cluster of thunderstorms will be weakening by
then. A quick shift to gusty northerly winds can be expected upon
arrival of the storms, shifting back southwest within an hour or
two. Storms will be capable of strong wind gusts.

In the moist air mass, IFR and LIFR cigs under 1,000 feet will
again develop across a broad area in the hours around sunrise on
Saturday morning. Clouds will quickly lift and scatter starting an
hour or two after sunrise. Seabreeze-driven thunder could already
be developing before the end of the valid period.

&&

.MARINE...
Issued at 349 PM EDT Fri Aug 11 2023

High pressure situated just southeast of the waters will maintain
fairly tranquil conditions this weekend into early next week with
westerly winds around 10 knots and seas around 2 feet. However,
expect locally higher winds and seas in and around thunderstorms.

&&

.FIRE WEATHER...
Issued at 349 PM EDT Fri Aug 11 2023

Extreme heat will be a big concern for those working outdoors this
weekend. Sunday may be the hottest day, with heat index values of
110 to 120 degrees possible. Otherwise, gusty and erratic winds
near afternoon thunderstorms will be the other fire weather
concern through early next week.

&&

.HYDROLOGY...
Issued at 349 PM EDT Fri Aug 11 2023

Locally higher rainfall amounts through Saturday may result
in some poor drainage flooding, while the probability of flash
flooding is low. Relatively drier on Sunday and Monday, with
a wetter pattern thereafter as a front moves into the region.

&&

.SPOTTER INFORMATION STATEMENT...

Spotter activation is requested. Spotters should safely report
significant weather conditions and/or damage by calling the
office or tweeting us @NWSTallahassee.

&&

.PRELIMINARY POINT TEMPS/POPS...
Tallahassee   77  99  77  98 /  30  50  20  40
Panama City   81  94  80  94 /  20  30  20  30
Dothan        75  98  76  98 /  30  50  20  50
Albany        74  98  77  98 /  30  30  20  40
Valdosta      75  98  77  98 /  50  20  10  40
Cross City    78  97  78  97 /  10  40  10  30
Apalachicola  81  94  81  93 /  10  40  20  20

&&

.TAE WATCHES/WARNINGS/ADVISORIES...
FL...Heat Advisory until 8 PM EDT this evening for FLZ019-028-029-034-
     128-134.

     Excessive Heat Warning from 11 AM EDT /10 AM CDT/ to 8 PM EDT /7
     PM CDT/ Saturday for FLZ007>019-026>029-034-108-112-114-115-
     118-127-128-134.

     Excessive Heat Watch from Sunday morning through Sunday evening
     for FLZ007>019-026>029-034-108-112-114-115-118-127-128-134.

     Excessive Heat Warning until 8 PM EDT /7 PM CDT/ this evening
     for FLZ007>018-026-027-108-112-114-115-118-127.

     High Rip Current Risk until midnight EDT /11 PM CDT/ tonight for
     FLZ108-112-114.

GA...Heat Advisory until 8 PM EDT this evening for GAZ142>148-155>161.

     Excessive Heat Warning from 11 AM to 8 PM EDT Saturday for
     GAZ142>145-155>160.

     Excessive Heat Watch from Sunday morning through Sunday evening
     for GAZ120>131-142>148-155>161.

     Heat Advisory from 11 AM to 8 PM EDT Saturday for GAZ120>131-
     146>148-161.

AL...Heat Advisory until 7 PM CDT this evening for ALZ065>069.

     Excessive Heat Warning from 10 AM to 7 PM CDT Saturday for
     ALZ065>069.

     Excessive Heat Watch from Sunday morning through Sunday evening
     for ALZ065>069.

GM...None.
&&

NEAR TERM...Haner
SHORT TERM...LF
LONG TERM....LF
AVIATION...Haner
MARINE...LF
FIRE WEATHER...Haner
HYDROLOGY...LF

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