Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 311505
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1105 AM EDT WED AUG 31 2016

.SYNOPSIS...
Tropical Depression Nine is expected to intensify into a tropical
storm and track from the eastern Gulf of Mexico northeast across
northern Florida and off the Southeast U.S. coast through Friday.
Cooler and drier high pressure will then return from the north this
weekend and persist into early next week, before the high settles
overhead for the middle of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Today: Weak low pressure offshore will shift north toward the SC
coast. This will bring a pretty good chance of showers and a few
thunderstorms to the area today, especially near the coast. Some
of the rain could be heavy at times. Otherwise another warm and
muggy day is on tap with highs mainly in the upper 80s most inland
spots and a bit cooler at the beaches.

Tonight: Low pressure will continue to move north along and near
the SC coast which will lead to lowering rain chances from west to
east, although a trailing trough will keep pretty good rain
chances near the coast through the period. Could see some fog
develop late inland as winds slacken. Low temperatures mainly
in the lower to mid 70s.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY/...
Our forecast for late this week revolves around the tropical cyclone
in the Gulf of Mexico, with the latest consensus of the models and
the official NHC forecast showing landfall over the FL Big Bend
region Thursday Night, before traveling more quickly Northeast over
or near the coast of the region on Friday.

A short wave trough over the central U.S from today will dig
southeast to the northeast Gulf of Mexico, picking up the cyclone
and allowing for it to eventually accelerate northeast. While the
model consensus and the official forecast for NHC is in close
agreement with that consensus, any slight deviation in the track,
intensity and it`s timing will have implications on our forecast.
However, probabilities have increased where we`ll require tropical
headlines at some point later today, and the risk for heavy rains,
tropical storm force winds and severe weather have also increased.
Storm surge could become more of a concern, pending the exact track.

As of this time the worst impacts look to occur Thursday Night into
Friday, maybe lingering into Friday Night over the far northern
zones if the system is slower in lifting northeast. We have added
mention of heavy rains to the gridded forecast during this time
along with categorical PoP for just about everywhere at some point.

The tropical cyclone will likely to be in at least a somewhat
sheared environment for its passage over the area, which means that
the strongest winds, heaviest rain and isolated tornadoes would
occur to the east of the center. So you are advised not to focus too
much on the exact center of the storm (unless it turns out to be
stronger than now anticipated). For now though there is the
potential for tropical storm force winds to occur, with the
greater potential along and near the coast, with less chance far
inland.

Severe Weather...Now that the most recent track forecast is a nudged
a  little further left than earlier forecasts, the risk for
tornadoes are now greater than previously thought. Typical in
landfalling tropical cyclones the risk for tornadoes will be
greatest near and east of the center of the system. Strong low level
directional shear and at least 30 kt of 0-1 km Bulk Shear will
support the potential for isolated tornadoes late Thursday into
Thursday Night for SE GA, and later Thursday Night into Friday for
southern SC. While SHERB values are progged less than a unit of 1.0,
the Significant Tornado Parameter is forecast as high as 1.0-1.5.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
Much more relaxed conditions will prevail through the extended
period, under the influence of high pressure that builds from the
north through Labor Day, and then aligns itself east-west across the
region for the middle of next week. Temps will be a little below
average into early next week, before some modification in temps
occur for Tuesday and Wednesday.

&&

.AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...
Weak low pressure will meander southeast of our area today, then
move northeast along the SC coast tonight. Brief flight
restrictions are possible in SHRA or maybe an isolated TSRA. Given
the terminals are more likely to see VFR, we`re forecasting it as
prevailing in the TAFs. Abundant moisture trapped beneath the
nocturnal inversion will allow for conditions to drop down into at
least the MVFR range in low stratus late tonight.

Extended Aviation Outlook: Periodic flight restrictions are possible
at KSAV and KCHS Thursday, with a higher risk of flight restrictions
Thursday Night into at least Friday, as the long anticipated
tropical cyclone moves into and through the area. Expect strong
winds (possibly to tropical storm force) in association with this
system, especially late Thursday Night and Friday, maybe even into
Friday Night at KCHS if the system is slower in exiting.

&&

.MARINE...
Today and Tonight: Weak low pressure off the northern FL/GA coast
this morning is expected to shift northward near the SC through
tonight. Mainly east/southeast winds ahead of the low will
diminish and veer to southwest/west tonight. The strongest winds
look to be beyond 20 nm where gusts to 25 knots and seas to 7 feet
are expected. Thus, a Small Craft Advisory will remain in effect
for our offshore GA waters. Mariners should also expect a good
chance of heavy showers and a few thunderstorms.

Conditions for marine interests will gradually deteriorate late this
week in response to the tropical cyclone that we have been
monitoring for more than a week, before improving weather settles in
for the Labor Day weekend.

The nose of sub-tropical Atlantic High Pressure will poke in from
the east-southeast Thursday between weak low pressure departing off
the coast of NC, and the tropical cyclone heading through the NE
Gulf. However, the tropical cyclone could be gaining strength
before it makes landfall and moves through north FL and into
southern GA before daybreak Friday. The system then lifts over or
near the waters during Friday, before pulling rapidly away Friday
Night. Continental High Pressure then builds in for Saturday into
early next week.

Tropical headlines will be required at some point later today, and
will likely remain in effect for at least tropical storm conditions
expected over much of the maritime community through Friday or
Friday Night. The forecast may require future adjustments, so
continue to monitor the latest information from The National
Hurricane Center and NWS Charleston.

Rip currents: High risk of rip currents continues today due to
swell from Gaston, persistent onshore winds, and high tidal
ranges.

Astronomical influences from the New Moon, long period
swells, and increasing onshore winds in association with the
tropical cyclone will lead to an enhanced risk of rip currents
through Friday. There have been numerous reports of rip currents
the past several days and conditions will only get worse due to
the tropical system.

&&

.TIDES/COASTAL FLOODING...
There is a risk of shallow coastal flooding around the times of
high tide through Friday. With the approach of the tropical
cyclone the risk for more substantial coastal flooding and
widespread significant beach erosion could certainly occur.

&&

.CLIMATE...
Top 5 Warmest Augusts Based on Mean Temperature...

KCHS...
1. 83.9...2016 (through August 30th)
2. 83.7...2007
3. 83.5...1987
4. 83.3...2010
5. 83.2...2011

KSAV...
1. 84.8...2011
2. 84.6...1878
3. 84.5...1987
4. 84.4...2016 (through August 30)
5. 84.3...1938

KCXM...
1. 84.3...1999
2. 84.2...1900
3. 84.1...1998
   84.1...1954
5. 83.6...2016 (through August 30)

The consecutive streak of 90F or greater at Savannah came to an
end yesterday after 69 straight days.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...High Risk for Rip Currents until 8 PM EDT this evening for
     GAZ117-119-139-141.
SC...High Risk for Rip Currents until 8 PM EDT this evening for
     SCZ048>051.
MARINE...Small Craft Advisory until 8 PM EDT Thursday for AMZ374.

&&

$$
SYNOPSIS...
NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...
TIDES/COASTAL FLOODING...
CLIMATE...


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