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FXUS62 KCHS 231924
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
324 PM EDT Sat Aug 23 2025

...THE RISK FOR FLASH FLOODING AND COASTAL FLOODING CONTINUES...

.SYNOPSIS...
A front will remain stalled over the region through Sunday as
waves of low pressure pass by. A much stronger cold front will
clear the area Monday night with high pressure prevailing
through the middle of next week.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
The wet pattern continues. Convection is showing a slight
consolidation along the far southern South Carolina and upper
Georgia coast this afternoon where low-level convergence is the
strongest. The atmosphere remains very moist and weakly unstable
with long/skinny CAPE profiles. This setup is ideal for
efficient rain making with rainfall rates being augmented by
warm cloud processes. Near term high-resolutation guidance has
been struggling a bit today, but there may be slight uptick in
both rainfall rates and rain coverage later this afternoon as
instability builds slightly in response to a thinning of the
cloud canopy. The risk for flash flooding continues for the rest
of the afternoon and the Flood Watch remains in effect through 2
AM Sunday. Some places across Charleston County, including
Downtown Charleston, have seen upwards of 8-10.5" in the past
24-30 hours alone.

The remains some uncertainty on how convection will trend later
this evening and overnight. Guidance has been consistent in
showing one last frontal low developing along the stalled front
later this evening as shortwave energy passes overhead. The wave
is forecast to trek just offshore of the lower South Carolina
coast, but is exact path is still in question. This will have
implications on where any type of secondary convergence axis and
resulting bands of additional heavy rain will up near the lower
South Carolina coast. It does appear the lower South Carolina
coast, especially the Charleston County coast, will likely see
the highest rainfall potential overnight as the low passes by,
but any bands of heavy rainfall could very well end up near or
just offshore. This will have to closely monitored through the
evening hours, especially with the tide level in the Charleston
Harbor (904 PM) likely to make a run for the high-end moderate
if not major flood level. For now, likely to categorical pops
were maintained through the evening hours with the better rain
chances shifting to the coast overnight. Lows will range from
the upper 60s/near 70 well inland to the mid 70s at the beaches.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/...
By Sunday morning, the frontal boundary and associated weak
surface low pressure is expected to be just off the coast.
Aloft, the region is out ahead of a deepening trough over the
Ohio River Valley which will lift the surface low
northeastwards, with marginally drier and cooler air being
advected in on the backside. While the 12Z hires convection-
allowing models (CAMs) point towards mostly some spotty light
showers to be expected throughout the day, medium/long range
models think that coverage is going to be a bit more widespread.
Regardless, any rainfall amounts are expected to be light with
no renewed flooding concerns. Afternoon highs in the mid to
upper 80s are expected, and with the continued dew points in the
lower to mid 70s heat index values top out in the mid 90s along
the coast and lower 90s inland.

Heading into Monday, the aforementioned trough has been
developing a strong surface low pressure near Hudson Bay,
sending a separate cold front into the eastern CONUS from the
northern plains. After a quiet start to the day, instability
builds with potentially up to near 2000 J/kg of CAPE by the
afternoon hours. With both a sea-breeze and approaching cold
front to trigger showers and thunderstorms, a strong to severe
thunderstorm cannot be ruled out, though shear. The vast
majority of AI/ML algorithms at this time would suggest little
to no chance for severe weather, with SPC also not carrying an
outlook. Depending on what time and if convection gets started,
near seasonal high temperatures are expected in the lower 90s.

For Tuesday, the trough axis still hasn`t swept through the
region yet, keeping the main cold front off to our west out
ahead of a surface high pressure over the Ohio River Valley.
Mostly dry conditions are expected as cooler and drier air
filters into the area (with dew points in the 60s!), and
afternoon highs in the mid to upper 80s.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
Broad high pressure will shift over central Appalachian with
the forecast area located within its southeastern fringes
Tuesday night into Wednesday. The greatest moisture looks to
remain offshore and to our south, resulting in at best isolated
to perhaps scattered showers/thunderstorms developing mainly
along the sea breeze mainly in the afternoon hours. Otherwise,
much drier conditions are forecast especially for locations
inland. Below normal temperatures are expected for the second
half of the week.

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
23/18z TAF Discussion:
KCHS/KJZI: MVFR conditions will prevail for much of the period
as bands of showers move near the terminals. Cigs may start out
VFR, but should lower back into MVFR by 20z. Showers timing is
proving difficult, but expect some degree of banding to work
through during the rest of the afternoon. Another more
consolidated area of rain could spread into the terminals 08-12z
as low pressure exits the area. There is a risk for IFR cigs to
filter in as the low meanders farther offshore, but confidence
was not high enough to include a mention just yet.

KSAV: Showers will continue to impact the terminal through mid-
afternoon. Activity should wane as the evening approaches.
Widespread IFR cigs should filter in after sunset as low
pressure begins to organize offshore. Cigs may approach
alternate minimums, which was handled via TEMPO group 09-12z for
now. IFR should lift to MVFR by mid-morning Sunday.

Extended Aviation Forecast: Flight restrictions are possible
into early Sunday evening during showers/thunderstorms
impacting CHS/JZI/SAV terminals. The risk will diminish Sunday
night into Monday as drier air filters into the region behind
departing low pressure.

&&

.MARINE...
Tonight: Low pressure will pass across the waters tonight
resulting in northeast winds backing to north. There may be a
slight enhancement/pinching of the pressure gradient as it does,
mainly across the South Carolina waters. Gusts could get as
high as 20 kt. Right now, it looks too marginal to hoist a Small
Craft Advisory, but this will need to be monitored, especially
from South Santee-Edisto Beach out 20 NM.

Sunday through Thursday: Offshore winds will prevail Sunday
into Monday as a weak coastal low departs to the northeast. A
cold front will push offshore late Monday night causing winds to
shift out of the northeast and prevail through the remainder of
the period. Both winds and seas look to remain below Small
Craft Advisory levels. No marine concerns expected through the
period.

Rip Currents: A moderate risk for rip currents is in place for
all beaches through this evening due to lingering swells
generated from Erin.

&&

.TIDES/COASTAL FLOODING...
A weak mid-level wave (piece of positive vorticity) is
currently pushing east along a stalled cold front across
southern Georgia. Latest observations show broad cyclonic flow
over southern Georgia with pressure slowly falling at Savannah.
As the wave ejects east off of the Georgia coast, a weak surface
low will form. Already winds are out of the northeast with
intermittent wind gusts to 15 kt or so (KHXD gusted to 16 kt and
KJZI gusted to 14 kt). Simultaneously, rainfall totals near the
coastal tidal sites have been in the 6" to 10" range. The Ekman
transport from the northeast winds and the freshwater runoff
has all come together to pump tidal departures even higher
compared to this time yesterday. At Charleston Harbor yesterday,
the tidal departure peaked between high and low tide around
+2.18 ft, while today it peaked at +2.36 ft. At Fort Pulaski,
the tidal departure peaked between high and low tide around
+2.24 ft, while today it peaked at +2.90 ft.

Charleston Harbor: Given the numbers above, the new high tide
forecast calls for a +2.0 ft departure with crest at 8.1 ft
MLLW, or major flooding.

Fort Pulaski: The new high tide forecast call for a +2.0 ft
departure with a crest at 9.9 ft MLLW, or minor flooding.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Flood Watch until 2 AM EDT Sunday for GAZ087-088-099>101-
     114>119-137>141.
     Coastal Flood Advisory from 7 PM to 11 PM EDT this evening for
     GAZ117-119-139-141.
SC...Flood Watch until 2 AM EDT Sunday for SCZ040-042>045-047>052.
     Coastal Flood Advisory from 7 PM to 11 PM EDT this evening for
     SCZ048-051.
     Coastal Flood Warning until midnight EDT tonight for SCZ049-
     050.
     Coastal Flood Advisory until midnight EDT tonight for SCZ052.
MARINE...None.

&&

$$

NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...