Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 240759
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
359 AM EDT Sun Sep 24 2017

.SYNOPSIS...
High pressure will prevail through this weekend. The high will
weaken and shift inland as Hurricane Maria tracks northward off
the Southeast U.S. coast through the first half of next week. A
cold front will approach the forecast area late next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Pre-dawn: Patches of high clouds were across the region early
this morning. The special 06Z sounding from KCHS indicated
a low level profile which does not appear as moist as the
previous couple of mornings with close to 20 knots of wind atop
the boundary layer. This suggests a diminished chance of low
stratus this morning and only some ground fog inland areas.

Today: Quite a bit of mid level NVA on the west subsidence flank
of Hurricane Maria is forecast to develop across the forecast
area. We anticipate dry weather across the area today, with only
a very small risk for a couple spotty light showers with the
sea breeze along the Altamaha River this afternoon. While only
scattered diurnal cumulus are expected, we should see an
increase in high cloud cover across the region associated with
a southerly 50 knot 250 MB jet atop the area. We did not alter
high temps today since high clouds are unlikely to thicken until
later in the day.

Tonight: Dry weather will continue with high clouds more
prevalent across SC than over southern GA given the forecast
alignment of the upper jet segment and position of Maria. No
fog concerns are foreseen at this time, given the boundary
layer gradient and wind fields. Lows in the mid to upper 60s,
lower 70s at the beaches and barrier islands.

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY/...
Dry high pressure will remain situated over the forecast area Monday
as Hurricane Maria travels north offshore. Models continue to show
PWats 0.25 to 0.5 inches below normal under subsidence sufficient
enough to preclude precipitation formation. Heights aloft could fall
slightly by late Tuesday as the core of Hurricane Maria potentially
becomes less symmetric in advance of an approaching trough. Ambient
moisture will also gradually rebound through this period. Under the
right conditions, some slightly increased probabilities of periodic
showers late Tuesday into Wednesday would appear warranted,
primarily across coastal SC and over the coastal waters nearest the
tropical system. That said, mostly dry conditions still appear
reasonable for the forecast area at this time. Above normal
temperatures will persist, with highs in the mid to upper 80s and
lows in the mid to upper 60s, around 70 at the beaches.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
Despite the presence of Maria offshore, weak NVA under high pressure
should continue to help mitigate precipitation chances initially.
Chances for showers/thunderstorms will increase later in the week
into early next weekend due to an approaching cold front. Guidance
continues to suggest that the front will cross the Appalachians
Thursday into Friday, with passage through the forecast area likely
by early Saturday. Above average temperatures will persist in
advance of the front, with cooler temperatures and lower dewpoints
likely behind the front as cool high pressure builds back into the
area.

&&

.AVIATION /08Z SUNDAY THROUGH THURSDAY/...
VFR conditions expected across KCHS and KSAV through the 06Z
TAF period. Winds are forecast to shift from the NE around
midnight and continue through Sunday. Deepening mixing and
momentum transfer should support low end gusts during the
daylight hours across SC, KSAV should see less gust potential.

Extended Aviation Outlook: Mainly VFR conditions expected with low
probabilities for restrictions in the mornings due to fog.

&&

.MARINE...
The pressure gradient between high pressure over the Great Lakes
and Hurricane Maria will be sufficiently strong enough to
support 15-20 knots of northeast flow over much of our waters
through tonight. Winds will be strongest beyond 20 NM offshore
will typical diurnal variations closer to the land/sea
interface. The bigger issue will be the building long period
swell from the offshore hurricane. We made little deviation from
6-8 ft seas near shore and 9-11 ft over outer GA waters.

Monday through Thursday: A prolonged period of Small Craft
Advisories will continue due to high seas pushing into the waters
from offshore Hurricane Maria. Generally northerly winds may
occasionally tip NE and will remain 15 to 20 knots with some gusts
to 25 knots Monday into early Tuesday before backing NW late Tuesday
into early Wednesday. Latest guidance suggests seas will remain
above Small Craft Advisory criteria through Wednesday afternoon or
evening.

Rip Currents: Swell from offshore Hurricane Maria will continue
to build at the beaches. This resulting in a high risk of rip
currents today. Due to the presence of Hurricane Maria offshore,
increased chances for life-threatening rip currents will
persist into mid-week.

&&

.TIDES/COASTAL FLOODING...
Powerful surf created by offshore Hurricane Maria will drive
significant wave run-up, which could cause further beach erosion
this weekend into early next week. High Surf Advisories are in
effect today and Monday. Also, the potential for shallow salt
water flooding will persist through early next week around the
times of high tide, particularly along the South Carolina coast.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...High Rip Current Risk through this evening for GAZ117-119-139-
     141.
     High Surf Advisory until 8 PM EDT Monday for GAZ117-119-139-
     141.
SC...High Rip Current Risk through this evening for SCZ048>051.
     High Surf Advisory until 8 PM EDT Monday for SCZ048>051.
MARINE...Small Craft Advisory until 8 PM EDT Tuesday for AMZ352.
     Small Craft Advisory until 4 PM EDT Wednesday for AMZ350-374.
     Small Craft Advisory until 5 AM EDT Tuesday for AMZ354.

&&

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


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