Purysburgh, South Carolina Weather Forecast Discussion

451
FXUS62 KCHS 131042
AFDCHS
Area Forecast Discussion
National Weather Service Charleston SC
642 AM EDT Sat Sep 13 2025
.SYNOPSIS...
High pressure will extend across the region into next week.
Weak low pressure may develop offshore Monday before moving
farther out into the Atlantic.
&&
.NEAR TERM /THROUGH TONIGHT/...
Latest 250 mb analysis revealed anticyclonic flow across the central
United States with a trough axis located to the west and east.
Towards the Canadian Maritimes, another stronger shortwave will
dive southeast and wave break, helping to further amplify the
ridging across the central United States. For coastal SC and GA,
the mid- level weakness will center along the coast with the
ageostrophic divergence setting up offshore. The means more high
clouds are forecast over coastal SC today as the 250 MB jet
axis impinges from the east. As this occurs, less than 1" PWAT
air will slide down the eastern side of the Appalachians with
forecast soundings clearly showing this as the dewpoint trace
pulls apart at all levels from the temperature trace. There will
likely be cumulus right along coastal SC today, but inland and
towards GA even CU will be lacking. Expect high temperatures
in the lower to mid 80s (as 1000/ 850 mb thicknesses keep
around or below 1400 m) with no precipitation expected.
&&
.SHORT TERM /SUNDAY THROUGH TUESDAY/...
The sharp upper trough aligned along the Southeast U.S. coast is
forecast to gradually cut off into an upper-level cyclone Monday as
the feature becomes increasingly detached from the main belt of the
westerlies. As the upper low become increasingly better defined,
there is a chance that weak surface cyclogenesis could occur
somewhere off the South Carolina coast along the pronounced coastal
trough noted well offshore. Where the non-tropical surface low will
track and its strength is very much uncertain as much will be
dependent on exactly where the upper low forms in response to
upstream ridging over the Ohio Valley and Great Lakes regions. Most
of the GFS and ECMWF ensemble members show a much weaker system
compared their operational counterparts with only a few members
showing a well-defined cyclone, more so with the ECMWF members.
For sensible weather, a wedge of dry high pressure will remain place
with the greater chances for any measurable rainfall holding well
offshore with the coastal trough. A rouge low-topped shower or two
moving onshore can not be completely ruled out along parts of the
Georgia coast where low-level steering trajectories are the most
favorable due to the orientation of the coastline, but dry
conditions will generally prevail across the South Carolina
Lowcountry into Southeast Georgia. For Monday, this part of the
forecast will be heavily influenced by any potential surface low
that develops offshore. Given the ongoing uncertainty here, there
was no reason to deviate from the 13/01z NBM which shows net
moisture values increasing slightly across the coast with rain
chances increasing ever so slightly, especially over the South
Carolina Lowcountry along/east of I-95. Pops will range from 20-30%
east of I-95 (highest Charleston Tri-County) with 10% or less
elsewhere. Highs will generally remain the lower-mid 80s through the
period with some upper 80s creeping in across far interior Southeast
Georgia by Monday. Lows will drop in the lower-mid 60s inland with
upper 60s/lower 70s at the beaches each night. A few more sheltered
spots could drop into the upper 50s, although these instances should
remain fairly isolated.
&&
.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
Mostly quiet conditions will persist through much of the upcoming
week as the upper low across the Carolinas gradually weakens and
ejects out to the northeast by Wednesday. The inland high pressure
wedge is forecast to strengthen as ridging builds in behind the
departing upper low. Any meaningful chance for measurable rainfall
will generally remain confined to the coastal waters and especially
near the west wall of the Gulf Stream. High temperatures will warm
through the period, peaking in the upper 80s/lower 90s Thursday and
Friday. Overnight lows will follow a similar pattern with lows
dropping into the 60s away from the beaches each night.
&&
.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
Saturday 12z TAFs: VFR through the issuance expected. Surface
high pressure is currently centered across western PA with dry
air filtering south down the eastern side of the Appalachians.
As this occurs, forecast soundings rapidly dry out with no
stratus forecast this morning. Winds will be out of the
northeast with some gusts up to 20 kt possible as the pressure
gradient tightens. Peak wind gusts will likely occur late
morning, and then winds will slacken in the afternoon slightly
as the coastal trough nudges to the east. No precipitation is
expected.
Extended Aviation Forecast: There are no high confidence
concerns.
&&
.MARINE...
Today and Tonight: Northeast winds have started to come up across
all waters this morning with buoy 41008 now gusting to 25 kt. As
such, the Small Craft Advisory is now in effect for all Atlantic
waters. Charleston Harbor remains out of the Advisory at this time.
A weak surface low is forecast to form well off the coast of SC this
afternoon, but it will have the affect of tightening the pressure
gradient across the open Atlantic waters. The offshore GA waters
beyond 20 nm could have gusts approaching gale (around 30 kt).
Sunday through Thursday: Pinched gradient conditions between inland
high pressure and a coastal trough offshore look to hold through much
of the week. There is a chance that weak low pressure could develop
offshore by Monday, but its strengthen and track are highly
uncertain. Any low that forms could have a local impact, but to what
degree remains unknown. For now, northeast wind and wind gusts as
well as seas will remain very near Small Craft Advisory conditions
for all but the Charleston Harbor through the week and the end times
of the various advisories that are already in effect have been
adjusted to reflect this. Winds and wind gusts may flirt with
advisory levels in the Charleston Harbor, especially near the harbor
entrance, but confidence is too low to hoist any advisory flags just
yet.
Rip Currents: The combination of persistent northeast winds,
astronomical factors, and elevated swell will yield a High Risk
of rip currents at all area beaches for the afternoon.
For Sunday, gusty northeast winds will persist within pinched
gradient conditions. Gusty northeast winds coupled with 4-5 ft
swells with 8 sec periods will a continued high risk for rip
currents along the Georgia beaches and a moderate risk for the South
Carolina beaches.
&&
.TIDES/COASTAL FLOODING...
Total water levels will remain elevated through the middle of next
from large tidal departures due to a pinched pressure gradient with
elevated northeast winds. The potential for coastal flooding will
continue though through the weekend, especially for coastal portions
of Charleston and Colleton Counties.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...High Risk for Rip Currents through this evening for GAZ117-119-139-
     141.
SC...High Risk for Rip Currents through this evening for SCZ048>051.
     Coastal Flood Advisory from 11 AM this morning to 3 PM EDT
     this afternoon for SCZ049-050.
MARINE...Small Craft Advisory until 6 PM EDT Tuesday for AMZ350.
     Small Craft Advisory until 2 AM EDT Tuesday for AMZ352.
     Small Craft Advisory until 2 PM EDT Monday for AMZ354.
     Small Craft Advisory until 2 AM EDT Wednesday for AMZ374.
&&
$$
NEAR TERM...Haines
SHORT TERM...
LONG TERM...
AVIATION...Haines
MARINE...Haines

NWS CHS Office Area Forecast Discussion