Severe Thunderstorm Warning 439, NWS Tallahassee, FL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
1000 AM EDT FRI AUG 28 2015

.Near Term [Through Today]...

The 12Z TAE sounding showed quite an unstable environment with
mid-level lapse rates of about 7 C/km and MUCAPE of over 2200
J/kg. This matches up well with the RUC forecast, which shows
SBCAPE increasing to 2000-2500 J/kg over the next few hours. This
morning's sounding showed a PWAT of only 1.61", which is fairly
dry for us this time of year, but 10-15 knot 1000-700 mb flow will
help increase low level moisture through the day and is a
favorable seabreeze pattern for widespread coverage of
thunderstorms across the area. Local satellite and radar imagery
show storms already active across our eastern coastal waters and
making further inland progression than originally forecast this
morning, so bumped up PoPs a bit through the remainder of the
daylight hours. Lingering dry air in the mid-levels and moderate
instability could combine to produce an environment somewhat
favorable for downbursts. Isolated strong to severe storms will be
possible with gusty winds the main threat.

&&

.Prev Discussion [653 AM EDT]...

.Short Term [Tonight Through Sunday]...

An elongated area of +PV stretches from the Northeast, through the
central Gulf of Mexico this morning. By tonight this area will
split into two anomalies: a more progressive wave moving off the
Northeast coast and what will be a quasi-stationary wave over the
north-central Gulf. It won't be until Saturday night through
Sunday that this wave lifts through the Southeast. At the surface,
ridging will prevail across much of the eastern half of the
country. Locally, the ridge will be quite disturbed due to the
upper wave. Steering flow will generally have a south or
southeasterly component yielding a rather wet seabreeze regime
across the entire Tri-State area. Like the ridge, the seabreeze
will be far from ideal and enhanced by the upper level anomaly.
Thus, PoPs will be higher than normal through the weekend
(50-70%). High PoPs and plentiful cloud cover will keep afternoon
highs anywhere from the mid 80s to around 90 degrees. Overnight
lows will be in the middle 70s and not as pleasant as recent
nights as moisture surges back into the region.

.Long Term [Sunday Night Through Friday]...

The main feature in the extended range forecast will be what is
now Tropical Storm Erika. The eventual track will have a lot to do
with how Erika holds together as it moves across Hispaniola today.
The current track from NHC takes Erika south of the Bahamas before
curving it north along the immediate east coast of Florida. A
concerning trend in the dynamical models is a westward shift in
the track. Both the 00z GFS and ECMWF bring Erika into the eastern
Gulf, but diverge greatly with respect to timing. There has been a
lot of back and forth between the dynamical models and a great
deal of uncertainty still exists. But, the potential for at least
some sort of impacts locally from Erika appears to be increasing
over the past 24 hours. A track off the east coast of Florida will
bring minimal rain impacts to the Tri-State region, while a track
over the Peninsula will likely bring a great deal of rain over the
Suwannee Valley, and a track into the eastern Gulf would mean the
potential for both heavy rain and wind impacts area-wide. Due to
the uncertainty in this forecast and the latest trends, close
attention should be given to the forecast over the next couple of
days.

.Aviation...

[Through 12Z Saturday] VFR conditions are expected this morning,
with scattered to numerous showers and storms likely between 18Z
and 03Z. These showers and storms may affect any of the terminals
during that timeframe. This was handled in the TAFs with VCTS at
all of the terminals. Confidence was high enough in a particular
window where storms are more likely at VLD (21-01Z) to include a
TEMPO group with some gusty winds and IFR visibility. Similar
conditions (gusty winds and IFR visibility) will be possible in
any storms today, but confidence was not high enough in timing at
any of the other terminals to include additional TEMPO groups.

.Marine...

Light winds and low seas will prevail through the weekend. After
that, it will depend on Erika's track. No matter the track, at
least a slight increase in winds and possibly seas should be
expected starting next week.

.Fire Weather...

An increase in low-level moisture will keep RH levels elevated and
allow rain chances to increase from today into the weekend.

.Hydrology...

With a transition to a wetter pattern beginning today, expect
average rainfall amounts on the order of 1-1.5" over the next
three days. This will have little impact on area rivers. Next
week, the potential for some very heavy rain exists depending on
Erika's track. At this time, models suggest the possibility for
5-7" over a 48 hour period with Erika. Should the track shift
west, these amounts could spread into the southeast Big Bend and
south-central Georgia. Interests along the Suwannee River are
urged to pay close attention to rainfall forecasts over the next
few days.

&&

.Preliminary Point Temps/PoPs...

Tallahassee   91  75  86  73  90 /  50  40  60  30  50
Panama City   87  77  85  75  88 /  40  50  60  30  30
Dothan        91  73  85  70  89 /  50  40  60  30  30
Albany        91  73  86  71  89 /  50  40  60  40  40
Valdosta      91  74  87  73  90 /  50  40  60  30  50
Cross City    90  75  88  74  90 /  40  40  60  30  50
Apalachicola  89  77  85  76  87 /  50  60  60  40  30

&&

.TAE WATCHES/WARNINGS/ADVISORIES...
FL...NONE.
GA...NONE.
AL...NONE.
GM...NONE.
&&

NEAR TERM...MOORE
SHORT TERM...HARRIGAN
LONG TERM...HARRIGAN
AVIATION...LAMERS
MARINE...HARRIGAN
FIRE WEATHER...LAMERS
HYDROLOGY...HARRIGAN