Seigling, South Carolina Weather Forecast Discussion

158
FXUS62 KCHS 221112
AFDCHS
Area Forecast Discussion
National Weather Service Charleston SC
712 AM EDT Mon Sep 22 2025
.SYNOPSIS...
High pressure north of the region will weaken on Monday. A
storm system could affect the area late in the week.
&&
.NEAR TERM /THROUGH TONIGHT/...
Today: Aloft, the forecast area will sit just downstream of a
mid-level trough starting to move east of the lower MS Valley.
At the surface, the setup will feature an inland wedge of high
pressure with a subtle trough off the coast. Through the day,
the inland high will weaken which should allow the offshore
trough to push some low-level convergence inland, primarily down
along the GA coast. The result should be increased convection
chances for the GA coast. This scenario is broadly supported by
the suite of hi-res models as well as the HREF. Also of note,
the best chances for the GA coastal zone should come from the
late morning through the early afternoon hours. Elsewhere,
virtually no diurnal convection is expected, but we can`t
completely rule out a rogue shower or thunderstorm. Rainfall
amounts for the GA coastal zone should mostly be half an inch or
less, but if a location sees multiple periods of showers it
could get in excess of half an inch. Highs are forecast to be
slightly above normal today, with mostly mid 80s for southeast
SC and mid to upper 80s for southeast GA.
Tonight: The aforementioned mid-level trough will continue to
push eastward but should deamplify and the pattern should start
to take on a more zonal flow look late. The surface pattern
should remain the same and we should see overnight precipitation
chances primarily across the coastal waters. Lows are forecast
to fall into the mid to upper 60s inland, and the upper 60s to
low 70s along the coast.
&&
.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
Tuesday: Surface high pressure that was over New England will
drift southeast towards Bermuda. The CAD will collapse Tuesday
afternoon with the coastal trough also washing out as the sea
breeze pushes inland. In the upper levels of the atmosphere, the
trough axis will be centered overhead with the upper level
divergence centered off of the SC coast. A small chance of
precipitation does exist for Tuesday, but the most likely
scenario is for a majority of the region to remain dry with weak
upper level convergence overhead. Highs will be in the upper
80s for South Carolina and low 90s for Georgia.
Wednesday: The upper level trough axis currently located over
British Columbia will progress eastward and wave break over the
Canadian Rockies and turn southeast towards Wyoming.
Constructive wave amplification will start to take place over
the Great Lakes with mid-level heights rising to around 591 dam
and 1000/850 mb thicknesses rising to 1420 m. Global ensembles
are in very good agreement here, with the NBM showing the IQR at
KCHS only being 3 degrees. High temperatures in the upper 80s
to lower 90s looks very likely. Heat index values will also be
in the upper 90s with some apparent temperatures reaching 100
degrees F. Most of the region will be dry on Wednesday.
&&
.LONG TERM /THURSDAY THROUGH SUNDAY/...
The latest runs of the GEFS/ GEPS/ and EPS are in fairly good
agreement for the extended. The most likely scenario is for the
upper level low over the Great Lakes to slowly move east through
the long term and slowly become vertically stacked. As this
occurs, the low will open up and eject east back into the main
flow over southeastern Canada. The details of how this occurs
does start to vary in the ensemble guidance. The GEPS tends to
show the weakest mid-level low with the quickest decay of the
wave as it is absorbed back into the main flow. The EPS and GEFS
show a stronger wave and slower decay/ absorption back into the
main flow. This slower progression would favor likely PoPs
Friday and Saturday with precipitation coming to an end on
Sunday. Temperatures will also trend down due to the increasing
cloud cover and precipitation chances.
&&
.AVIATION /12Z MONDAY THROUGH FRIDAY/...
The 12z TAF period begins with VFR conditions in place at KCHS,
KJZI, and KSAV. There could be brief periods of MVFR ceilings
through late morning as stratocumulus coming on shore
occasionally comes in with broken coverage. Then looking ahead
into the late morning and early afternoon, there should be more
shower activity along the GA coast than we have seen the past
few days. Right now it looks like this activity will stay mostly
south of KSAV so we don`t plan on adding any kind of shower
mention.
Extended Aviation Forecast: Mainly VFR expected through
Thursday morning. The chance of afternoon showers and
thunderstorms returns on Thursday with increasing chances on
Friday. Restrictions in ceilings and visibilities with some
gusty winds will be possible in any thunderstorms.
&&
.MARINE...
Today through tonight: Overall, northeast flow is expected to
prevail across the local waters through the overnight. Speeds
will be highest today, topping out in the 15-20 knot range at
times. Then overnight, speeds will diminish to become 5-10 knots
late. Seas should average 3-5 feet today, coming down a bit to
2-4 feet overnight.
Tuesday and Wednesday: The coastal trough will fall apart in
the afternoon as surface high pressure becomes established
northwest of Bermuda. Winds over the waters will veer from the
southeast and decrease in speed 5 to 10 kt. Seas will also start
to relax 2 to 4 ft.
Thursday: An upper level low and cold front will start to
approach the area from the west. Showers and thunderstorms will
return to the waters with winds and seas slowly ticking upwards.
This type of setup generally favor a slowing trend, meaning the
showers and thunderstorms might hold off until Friday.
Friday: Winds from the south around 10 kt with gusts 15 to 20
kt as a cold front approaches from the west. Showers and
thunderstorms likely. Seas 2 to 4 ft.
Rip Currents: A moderate risk of rip currents will prevail at
all area beaches through Tuesday due to increasing swell period
(up to 12 sec) and height (3 ft).
&&
.TIDES/COASTAL FLOODING...
Astronomical tide values will start to slowly fall Tuesday
through the remainder of the work week with northeast winds
veering around from the southeast. As such, total tidal
anomalies will also start to come down. No coastal flooding is
forecast at either Charleston Harbor or Fort Pulaski Tuesday
through the remainder of the week.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.
&&
$$
NEAR TERM...BSH
SHORT TERM...Haines
LONG TERM...Haines
AVIATION...BSH/Haines
MARINE...BSH/Haines

NWS CHS Office Area Forecast Discussion