Area Forecast Discussion
Issued by NWS Charleston, SC
FXUS62 KCHS 302006
Area Forecast Discussion
National Weather Service Charleston SC
406 PM EDT TUE AUG 30 2016
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 another area of low
pressure possibly develops offshore.
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Most of the activity over land will dissipate while convection
over the Atlantic waters lights up in association with the coastal
trough. This trough is expected to strengthen tonight, with fairly
strong moisture convergence resulting in good coverage of showers
and tstms mainly over the waters. However, scattered showers and
storms will likely affect mainly coastal areas through the night,
with a few showers drifting farther inland.
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...
A weak low pressure system off the Southeast U.S. coast will
deteriorate as it moves off toward the northeast through the day on
Wednesday. The strongest destabilization and forcing in the area of
the low will mainly remain offshore, though its proximity to the
coast will keep the potential for showers and thunderstorms in the
forecast for mainly Charleston County and the immediate coast of
Southeast South Carolina and Northeast Georgia. The highest moisture
values will remain off the coast with the low Wednesday, so the
flooding threat appears low other than low-lying areas at high tide.
Moving into Thursday and Friday, the primary challenge is nailing
down Tropical Depression 9`s impacts on the area. 12Z GFS and EURO
deterministic runs, as well as the majority of the GFS ensemble
runs, have trended the storm further north/closer to the coast as it
moves back into Atlantic waters Friday. Have increased QPF across
the area to account for this, with storm total rainfall amounts near
the coast now in the 4-6 inch range. While wind impacts from this
storm remain uncertain due to significant timing and strength
differences between models, there is growing confidence in flooding
being a threat with this storm (WPC has the immediate coast under a
marginal risk for excessive rainfall Thursday), especially if heavy
rainfall occurs around high tide in Downtown Charleston. Please
continue to monitor the latest forecasts as the situation will
become more clear in the coming days.
Northerly low and mid level flow will fill in as early as Friday
afternoon as the storm moves toward Cape Hatteras, bringing cooler
and drier conditions to the area.
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
The latest forecast from the NHC indicates a tropical storm will be
moving off the northeast FL coast overnight Thursday and then
staying offshore as it moves away from the GA/SC coasts through late
week. This will be followed by high pressure building from the north
this weekend into early next week. There is still quite a bit of
uncertainty regarding the track/strength of the tropical cyclone so
it is best to stay tuned to the latest forecast. Cooler and drier
conditions should then prevail for the weekend into Monday, although
a few showers can`t be ruled out from time to time mainly near the
coast. By Tuesday another area of low pressure could develop
offshore and head toward the coast.
.AVIATION /20Z TUESDAY THROUGH SUNDAY/...
VFR should prevail as showers dissipate into this evening.
Convective coverage and intensity will begin to increase around
daybreak, so brief flight restrictions are possible. Confidence is
not high enough to include this in the current TAFs.
Extended Aviation Outlook: Ceiling and visibility restrictions are
possible Wednesday and Wednesday night at both KCHS and KSAV as
showers and thunderstorms mainly offshore may approach the
terminals. Additional impacts from showers/thunderstorms and winds
are likely Thursday night into Friday, depending on the track of
Tropical Depression 9 which is forecast by the NHC to be a tropical
storm as it passes northeast off the GA/SC coasts.
The coastal trough has allowed east to northeast winds to
increase to as high as 15 kt. The wind waves combined with the
easterly swell has allowed combined seas to build to 6-7 ft over
the offshore GA waters. Therefore a Small Craft Advisory is in
effect for this zone.
Wednesday through Sunday: Weak low pressure off the Southeast coast
will bring easterly winds in the 10 to 15 kt range, with mainly 3 to
5 foot seas Wednesday and Wednesday evening. Conditions will
deteriorate rapidly early Thursday mornings as a tropical storm is
forecast by the NHC to move off the GA/SC coasts. Tropical Storm
force winds and seas as high as 5 to 10 feet are possible across the
local waters beginning Thursday night and lasting into Friday. There
is still some uncertainty in the strength/track of the tropical
cyclone so mariners should stay tuned to the latest forecasts.
Rip currents: Numerous rip currents were reported at area beaches
today. High risk of rip currents continues for Wednesday due to
solid groundswell from Gaston, persistent onshore winds, and high
Long period swells and onshore flow are expected to persist, thus an
enhanced risk will continue through at least Friday.
Tides remain elevated due to ongoing east/northeast winds, long
period swell and influences from the approaching new moon. A
Coastal Flood Advisory is in effect for the southeast South
Carolina coast for this evening`s high tide. Additionally, the
extratropical surge guidance suggests evening high tides through
Thursday will be very close to levels which would produce shallow
coastal flooding, especially along the lower South Carolina coast.
More Coastal Flood Advisories may eventually be needed.
GA...High Risk for Rip Currents through Wednesday afternoon for
SC...High Risk for Rip Currents through Wednesday afternoon for
Coastal Flood Advisory until 9 PM EDT this evening for
MARINE...Small Craft Advisory until noon EDT Wednesday for AMZ374.