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Area Forecast Discussion

375
FXUS62 KTAE 310533
AFDTAE

Area Forecast Discussion
National Weather Service Tallahassee FL
133 AM EDT WED AUG 31 2016

...Hurricane conditions possible over coastal portions of
Franklin, Wakulla, Jefferson, Taylor, and Dixie counties...

...Tropical storm conditions possible across inland portions of
the Florida Big Bend, Gulf county, and coastal Bay county...

.AVIATION [Through 06Z Thursday]...

VFR conditions are expected to continue at all TAF sites, with a
short period of MVFR to IFR CIGS possible in the FL Big Bend and
SW GA, including TLH, VLD, and ABY. Scattered SHRA/TSRA will
develop Wednesday afternoon with the best chances across southern
GA and the FL Big Bend. SHRA/TSRA chances are expected to increase
across the entire region this evening, yielding lower CIGS and
reduced vsby in and around any activity.

&&

.PREV DISCUSSION [911 PM EDT]...

.NEAR TERM [Through Tonight]...

The 11 AM EDT advisory of Tropical Depression Nine showed the
center to be about 340 mi west of Key West, FL. Despite being
well to our south still, the presence of this storm has increased
the pressure gradient over the Gulf coast, thus making for a
fairly gusty day across the area. Strong (>10 knot) 1000-700 mb
flow from the E/NE, as seen in our 12Z TAE sounding, will mean a
regime 3 sea breeze day, with sea breeze driven convection focused
mostly in south central GA and north FL. Local radar imagery shows
isolated storms already beginning to pop up in the eastern Big
Bend and in south central GA. These storms are forecast to become
more numerous through the afternoon and then dissipate around
sunset. Highs will be in the low to mid 90s, about 90 along the
immediate coast. Lows will be in the low to mid 70s, upper 70s
along the immediate coast.


.SHORT TERM [Wednesday Through Thursday Night]...

Main points:

Tropical cyclone to make landfall somewhere between Cape San Blas
and Tampa Thursday or early Friday

Storm surge flooding possible in Apalachee Bay with landfall

Inland flooding and isolated tornadoes possible near and east of
where center makes landfall

Latest models have trended a little west and slower in the
forecast track, and a little stronger in intensity


Multiple upper level short wave troughs will carve out a broad long
wave trough over the eastern third of the CONUS. A deep layer trough
will develop from the coast of the Carolinas to a tropical cyclone
in the central Gulf of Mexico by Wednesday morning. Along and east
of this trough there will be an increase in deep tropical moisture,
and we expect a rather sharp PoP gradient along this trough. The
aforementioned tropical cyclone, presumably a tropical storm by
that time, will translate northeastward along this trough, making
landfall somewhere between Cape San Blas and Tampa Thursday or
early Friday. There has been a trend in the most recent global
models and ensemble members in a slower, more westerly track, as
well as a stronger system. Our PoP and QPF forecasts have been
adjusted so that the higher values extend a little farther north
and west across our forecast area than previous forecasts, and is
now based on a track in between the NHC forecast from 11 am EDT
and this new guidance. Rain is likely from Tallahassee south and
eastward, especially Thursday through Friday morning, with the
heaviest and most persistent rain around Perry and Cross City.
Isolated tornadoes will also be possible.

The tropical cyclone is likely to be in at least a somewhat sheared
environment for much of its journey to the coast, which means that
the strongest winds, heaviest rain, isolated tornadoes, and storm
surge may occur to the east of the center; so don`t focus too
much on the exact center of the storm (unless it becomes stronger
and more symmetrical). As the system approaches the coast, the
storm- relative shear may decrease a bit, and upper level
divergence may increase through baroclinic influences. This may
allow for some intensification, though the consensus of NWP
models keeps the system just below hurricane strength.


.LONG TERM [Friday Through Tuesday]...

Once the tropical cyclone exits our region to the northeast Friday
and Saturday, our forecast area will be under sinking motion
aloft, situated between a 500 mb trough to the east and a ridge to
the west. The drop in deep layer moisture will keep PoPs below
average through much of the period. Temperatures will be near
average.


.MARINE...

Conditions will deteriorate as Tropical Depression Nine strengthens
into a Tropical Storm. The center is expected to track through the
marine area on Thursday with tropical storm conditions possible
across a large part of the area. The system is expected to exit the
region on Friday, yielding a gradual decrease in winds and seas
going into the weekend.


.FIRE WEATHER...

With a moist, tropical airmass in place, relative humidity values
will remain above critical thresholds through the period. No
hazardous fire weather conditions are expected.


.HYDROLOGY...

We expect the heaviest QPF to be across north FL, with storm
totals from Wednesday through Friday of 6 to 8 inches. Some of
this will occur ahead of the tropical cyclone, as deep tropical
moisture interacts with a trough on Wednesday. The QPF for the
rest of our region is more problematic, as some of the global
models forecast a more western landfall of the tropical cyclone.
This would of course increase the threat of heavy rain to our
western zones. We are not yet ready to completely commit to that
solution, but we have adjusted the QPF from Tallahassee north and
westward higher, and may have to go higher still if the recent
trend in models continues.

&&

.PRELIMINARY POINT TEMPS/POPS...

Tallahassee   93  77  84  76  91 /  40  60  80  70  50
Panama City   91  77  85  77  88 /  30  50  70  40  30
Dothan        92  74  91  73  92 /  10  20  40  30  30
Albany        95  74  88  74  91 /  20  20  50  50  30
Valdosta      91  74  84  74  87 /  50  50  80  80  50
Cross City    85  75  83  76  86 /  60  70 100  80  50
Apalachicola  90  78  84  77  88 /  40  70  80  60  30

&&

.TAE WATCHES/WARNINGS/ADVISORIES...

FL...Tropical Storm Watch for Coastal Bay-Coastal Gulf-Gadsden-Inland
     Dixie-Inland Franklin-Inland Gulf-Inland Jefferson-Inland
     Taylor-Inland Wakulla-Lafayette-Leon-Liberty-Madison.

     Hurricane Watch for Coastal Dixie-Coastal Franklin-Coastal
     Jefferson-Coastal Taylor-Coastal Wakulla.

GA...None.
AL...None.
GM...Tropical Storm Watch for Coastal waters from Apalachicola to
     Destin FL out 20 NM.

     Hurricane Watch for Apalachee Bay or Coastal Waters From Keaton
     Beach to Ochlockonee River Fl out to 20 Nm-Coastal Waters
     From Ochlockonee River to Apalachicola Fl out to 20 Nm-
     Coastal waters from Suwannee River to Keaton Beach out 20
     NM-Waters from Suwannee River to Apalachicola FL from 20 to
     60 NM-Waters from Apalachicola to Destin FL from 20 to 60
     NM.


&&

$$

NEAR TERM...Pullin
SHORT TERM...Moore
LONG TERM...Fournier
AVIATION...Pullin
MARINE...Moore
FIRE WEATHER...Fournier
HYDROLOGY...Moore



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