646
FXUS62 KCHS 220247
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1047 PM EDT Thu Aug 21 2025

.SYNOPSIS...
Weak high pressure will extend across the area tonight. A cold
front will stall over the Lowcountry and Southeast Georgia
Friday and will linger into the weekend. A much stronger cold
front will clear the area Monday with high pressure prevailing
through the middle of next week.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Tonight: Hurricane Erin will continue to move away from our area
while a front approaches from the north this evening. The front
should stall across the local area late within an environment
displaying deep moisture (PWATs 2.00 to 2.25 inches), which could
lead to few/scattered showers and thunderstorms after midnight.
Until the front arrives, radar trends indicate few to scattered
showers/thunderstorms ongoing across Southeast Georgia, and this
activity should continue through late evening given ample
moisture and numerous outflow/boundary interactions. The severe
weather risk associated with this activity is low given diurnal
heat loss post sunset, but the risk for heavy rainfall remains
during downpours associated with slow moving thunderstorms,
particularly near the Altamaha River where the most notable
coverage of precip and boundary interactions are expected.

Late tonight, isolated to scattered showers along with a few
thunderstorms are forecast across Southeast South Carolina with
the arriving front, while activity across Southeast Georgia
potentially lingers. Activity is still expected to remain sub-
severe, but there will remain a heavy rainfall risk given the
front stalling across the local area and ample moisture in
place. Low temperatures will range in the low 70s inland to mid
70s near the coast.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
Friday and Saturday: A cold front is forecast to stall over the
area Friday morning and linger into Saturday. Waves of low
pressure should develop and move east along the front as spokes
of vorticity pass through aloft. This coupled with building
PWATs of 2.25-2.50" and weak to moderate levels of instability
will support numerous to widespread showers/tstms through the
period. The steering flow will weaken with time with modified
soundings suggesting long/skinny CAPE profiles developing Friday
afternoon and lingering into Saturday. This will support
convection where warm cloud processes will support intense
rainfall rates, possibly >3 in/hr at times, given the rich,
tropical moisture plume that will be in place. This may lead to
areas of flash flooding, especially in the corridor roughly
south of a Reidsville-Springfield-Walterboro-Moncks Corner line
where 20cm soil moisture values are running in the >98th
percentile as of the 18 August analysis.

Given the saturated soil moisture profiles in place and the
intense hourly rainfall rates that are possible, the risk for
flash flooding will be elevated into Saturday evening,
especially in the coastal corridor where the evening high tides
both Friday and Saturday could enhanced the flood threat. A
Flood Watch has been issued from Friday morning through early
Sunday evening. Storm totals during this period will range from
2-4" with isolated amounts possibly exceeding 6". In fact, some
of the LPMM output from both the 21/00z and 21/12z HREF suggest
a potential for as much as 8-10" in spots over a rolling 24-hr
period. This certainly highlights the potential that some areas
could see some pretty hefty rainfall in about a 24 hour period.
Categorical pops 80-90% were highlighted during the afternoon
and evening periods both Friday and Saturday with 40-80% pops
overnight Friday. Considerable cloud cover and precipitation
will limit highs to the lower-mid 80s both afternoons with lows
dropping into the lower-mid 70s Friday night.

Sunday: Unsettled conditions will persist into Sunday as the
final frontal wave begins to pull away from the region. The
Flood Watch may need to be extended into the afternoon hours,
but this will depend on how much and where there axis of
heaviest rains set up prior to this. Thankfully, coverage does
not look as extensive. Pops were limited to 50-70%, highest
across the coastal corridor with highs limited to the mid-upper
80s.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
A strong cold front will push offshore Monday night. There is a
risk for isolated to scattered showers/tstms until FROPA. Cool,
dry air will filter in Monday night and lingering into at least
the middle of next week. Temperatures will average near normal
levels for Monday then fall to well below normal levels for
Tuesday and Wednesday.

&&

.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
TEMPO flight restrictions are possible at the SAV terminal due to
showers and thunderstorms impacting the terminal this evening.
Shower activity could develop/arrive at CHS/JZI tonight, leading
to flight restrictions as well, but confidence in timing/duration
of event is too low to include in the latest TAF issuance. The
greater concern for shower/thunderstorm activity is expected
Friday late morning and afternoon at CHS/JZI/SAV terminals, as
activity develops along/near a stalled front nearby. Conditions
will likely lead to prevailing MVFR groups at all terminals due
to showers, and possibly lower flight restrictions during TEMPO
TSRA between 18-22Z Friday. Later TAF issuances will likely need
to adjust timing of thunderstorm activity late morning and/or
afternoon Friday as convective trends become more clear.

Extended Aviation Forecast: An elevated risk for flight
restrictions from showers/tstms will persist for much of the
week.

&&

.MARINE...
Tonight: Hurricane Erin will continue to shift away from the
Southeast United States while a front approaches from the north this
evening, then stalls over or nearby overnight. As a result, seas
will continue to subside as the swell diminishes. The only Small
Craft Advisory left is for the GA waters beyond 20 nm and it should
end overnight.

Friday through Tuesday: There are no high confidence concerns
through Tuesday. A cold front will stall over the marine area
Friday and linger through the weekend, resulting in east to
northeast winds. A much stronger cold front will push offshore
Monday night with offshore winds prevailing late Monday night
into Tuesday. Both winds and seas look to remain below Small
Craft Advisory levels. Pockets of heavy rains Friday through the
weekend could reduce vsbys to 1 NM or less at times.

Rip Currents: The combination of lingering 3 ft swell and onshore
winds supports a Moderate Risk of rip currents Friday and again on
Saturday.

&&

.TIDES/COASTAL FLOODING...
Astronomical tide values at Charleston will remain elevated
with the evening high tide cycles Friday (6.23 ft MLLW) and
Saturday (6.11 ft MLLW). Minor coastal flooding will be possible
each evening, and Coastal Flood Advisories could be needed.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Flood Watch from 8 AM EDT Friday through late Saturday night
     for GAZ087-088-099>101-114>119-137>141.
SC...Flood Watch from 8 AM EDT Friday through late Saturday night
     for SCZ040-042>045-047>052.
MARINE...Small Craft Advisory until 2 AM EDT Friday for AMZ374.

&&

$$

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