880
FXUS62 KCHS 211133
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
733 AM EDT Thu Aug 21 2025

.SYNOPSIS...
Weak high pressure will continue to build into the region as
Hurricane Erin passes well offshore. The pattern may become
more unsettled again late week and into this weekend as cold
front stalls nearby.

&&

.NEAR TERM /THROUGH TONIGHT/...
Today: Erin will pull further away from the area today and as
it does we will lose the influence of the broader circulation
around it by the afternoon. The morning into the early to mid
afternoon looks to be pretty quiet as the airmass starts to
recover and precipitable water values climb. Hi-res models and
the HREF are then in good agreement that convection will
initiate along a subtle surface boundary that extends across
southeast GA. Coverage for the mid to late afternoon should
primarily impact southeast GA, perhaps extending across the
Savannah River into Hampton, Jasper, and Beaufort counties.
Overall, the severe weather threat does not look particularly
noteworthy with rather modest MLCAPE and DCAPE values depicted
by the hi-res models. Still, there could be a stronger storm or
two where outflow boundaries interact and enhance updrafts.
There will be at least a low end threat of locally heavy
rainfall thanks to precipitable water values rising to around 2
inches and storm motions on the order of 10 knots or so.
Temperatures will warm back up into the low to mid 90s for
highs, and with dewpoints lingering in the low to mid 70s we
should see heat index values into the low 100s for much of the
area. We could even see some heat indices as high as 105 along
and south of I-16, but expect conditions to remain below Heat
Advisory criteria (108 degrees).

Tonight: Ongoing convection from the late afternoon will
gradually work eastward toward the coast into the evening.
Through the rest of the evening and overnight we will likely see
at least some redevelopment of convection as boundary trailing
behind the long departed Erin becomes aligned across the
forecast area. While the focus for convection should shift to
the coastal waters, we could see clusters of showers and storms
across land areas through the night as we transition into a more
active period. Lows are forecast to fall into the low to mid
70s.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY/...
Friday: A weak cold front will likely stall nearby on Friday
and allow an ample amount of moisture to return. This will
likely cause scattered to numerous showers to develop across the
region on Friday. Heavy rainfall will be the main concern as
PWATs range from 2.25" to 2.50". Not surprisingly, WPC has
highlighted the region in a Slight Risk on Friday for Excessive
Rainfall. The 00Z HREF indicates an elevated risk of rainfall
with a 50-70% of 3", and/or possibly greater, occurring within
the span of 3 hours across portions of SE South Carolina and SE
Georgia on Friday into Friday night. Also, individual CAM
outputs indicating rainfall rates of 2-4"/hr possible. This also
aligns with the frontal placement with strengthening agreement
considering the model EAS probability signal for both >1" and
>2" across the region. Therefore, there is increasing confidence
that Flash Flood Advisories/Watches will likely be needed.
Thanks to the stalling cold front, highs will only reach into
the low to mid 80s across SE South Carolina and mid to upper 80s
across SE Georgia. Lows will dip into the low 70s inland and
then mid 70s along the coastline.

Saturday: This weak cold front will continue to stall nearby
and cause scattered to numerous showers and thunderstorms to
develop across the region on Saturday. Localized heavy rainfall
will be the main threat again on Saturday. WPC has highlighted
the region in a Marginal Risk on Saturday for Excessive
Rainfall.

Sunday: The region will be situated on the weak lee side of an
mid-lvl trough as the weak cold front continues to stall
nearby. This might be a duplicate of Friday and Saturday as it`s
possible to see locally heavy rainfall again across the region.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
A deep upper-lvl trough located south of the Hudson Bay seems
to get reinforced by another shortwave diving south out of
Canada. As this happens, constructive wave amplification will
occur and allow for a strong cold front to approach the region
on Monday. There is chance showers and thunderstorms to develop
out ahead of this front on Monday afternoon. Once this front
pushes across the region, a drier airmass will shift into the
CWA and allow for an appreciable drop in dewpoints. This will
also decrease the chance for precipitation on Tuesday and
Wednesday. Temperatures will be near and/or slightly below
normal for this time of year.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
The 12z TAF period begins with VFR conditions at KCHS, KJZI,
and KSAV. VFR conditions are expected to prevail through the
period at KCHS and KJZI as thunderstorm activity this afternoon
and evening should remain to the west and southwest across
southeast GA. However, KSAV will likely be right in the middle
of where thunderstorm activity will be concentrated this
afternoon. Therefore, we have maintained VCTS starting at 19z
as well as a TEMPO group for -TSRA from 20-23z. Also, late
tonight there could be increasing shower activity around KCHS
and KJZI so we have added in VCSH starting at 08z. Also, the
potential for restricted ceilings will increase, though the best
chances will likely come beyond the 12z TAF period.

Extended Aviation Forecast: Brief flight restrictions possible
at KCHS/KJZI/KSAV with afternoon showers and/or thunderstorms.

&&

.MARINE...
Today through tonight: Erin will continue to pull away from the
area and conditions across the local waters will steadily
improve. Northwest winds will continue this morning, then winds
will diminish significantly this afternoon as the gradient
weakens and 5-10 knots of flow is all that is expected through
the overnight. We`ve made some significant adjustments to seas
based on the fact that model guidance has been significantly
overdone for portions of the waters throughout the event. We
have initialized closer to the observed seas of 10-11 feet at
41004 and 4 feet at 41008. By the afternoon we should see 3-5
feet across all the nearshore waters and 5-7 feet in the outer
waters. Then late tonight seas will diminish to be 2-4 feet
across all waters. This necessitates some changes to the Small
Craft Advisories. We have cancelled the nearshore GA waters, and
moved the expiration time of the SC waters to the afternoon.
Finally, the outer GA waters continue the longest, expiring
Friday morning.

Friday: As the swell from Hurricane Erin continues to dial
back, seas will drop out to 3 to 4 ft. Expect east-northeasterly
winds at 10 to 15 kts with gusts up to 20 kts possible in
afternoon (mainly along the immediate coastline).

Saturday through Tuesday: Surface high pressure will dominate
the coastal waters through the weekend with east-southeasterly
winds at 10 to 15 kts. By early next week, winds will switch
more southwesterly ahead of an approaching cold front. Seas will
be 3 to 4 ft through the weekend, before tapering out to 2 to 3
ft on Monday and Tuesday.

Rip Currents/High Surf: While we are past the worst of the
swell associated with Erin, we will still see enough to yield a
High Risk of rip currents at all beaches today. Another High
Risk of rip currents is expected for Friday. Also, breaking wave
heights in the surf zone will improve significantly through the
day. Based on current observations at buoy 41008 we have
cancelled the High Surf Advisory for the GA coast. The SC coast
is now set to expire this afternoon.

&&

.TIDES/COASTAL FLOODING...
Upcoming evening high tide (~7:45 pm): Winds have turned
northwest and become unfavorable for elevated tidal departures,
but much of the wind influence is being balanced by the swell
from Erin and the water still loaded in the tidal system. At
Charleston, the astronomical tide is 6.27 ft MLLW, meaning we
would only need about 0.75 ft of departure to get at least minor
coastal flooding. Guidance supports potentially approaching
moderate coastal flooding (7.5 ft MLLW). A Coastal Flood
Advisory has been issued for coastal Colleton and Charleston
counties. At Fort Pulaski, current thinking is that we will fall
just short of minor 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...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.
     High Surf Advisory until 5 PM EDT this afternoon for
     SCZ048>051.
     Coastal Flood Advisory from 6 PM to 10 PM EDT this evening for
     SCZ049-050.
MARINE...Small Craft Advisory until 5 PM EDT this afternoon for AMZ350.
     Small Craft Advisory until 2 PM EDT this afternoon for AMZ352.
     Small Craft Advisory until 8 AM EDT Friday for AMZ374.

&&

$$

NEAR TERM...BSH
SHORT TERM...Dennis
LONG TERM...Dennis
AVIATION...BSH/Dennis
MARINE...BSH/Dennis