589
FXUS62 KCHS 201136
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
736 AM EDT Wed Aug 20 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: The main story of the day will be Hurricane Erin making
its closest passage to the southeast GA/SC coastline (~400
miles) and likely the peak of the peripheral impacts associated
with it. From the perspective of convection, today should be
very quiet as the forecast area sits solidly under the influence
of subsidence surrounding the large storm. The suite of hi-res
model solutions as well as probabilistic precipitation data from
the HREF strongly support there being little to no diurnal
convection today. We will see our strongest period of winds as
the gradient peaks, especially along and east of I-95 and along
the SC coast. Gusts as high as 20- 25 mph will be possible,
especially along the coast from Fripp Island north to the entire
Charleston County coast. We should also see increased cloud
cover this afternoon, mainly across the eastern half of the
forecast area. Temperatures are forecast to peak around 90 for
most of southeast SC, with low 90s across southeast GA.

Tonight: The area is expected to remain rain-free under the
influence of subsidence around Erin. The storm will move north
of the latitude of the forecast area and start to move further
away through the late night hours. Overnight lows should fall
into the low to mid 70s in most areas.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY/...
Thursday: Powerful Hurricane Erin will pass well offshore to
the northeast on Thursday morning w/ the circulation of Erin
expected to expand considerably throughout the day as it moves
farther away from the region across the Atlantic. This large
swell associated with Erin will finally begin to dial back
across the marine zones as Erin speeds away, however dangerous
surf and rip currents will continue through at least Friday.
Beachgoers should continue to follow advice from lifeguards,
local authorities, and beach warning flags. At the surface, a
weak surface high pressure will situate itself over southeast
Georgia. This will allow winds to swing from northerly to west-
northwesterly before tapering out in the afternoon. A good
amount of subsidence will remain across the region, and most of
southeast South Carolina should stay dry. However, there is some
indication that showers and thunderstorms could develop off the
seabreeze in the afternoon in southeast Georgia, and thus PoPs
were kept ~30%.

Friday and Saturday: A dissipating cold front will gradually
progress through the region on Friday morning. This front will
likely stall nearby throughout the weekend and allow for a great
deal of moisture to return. Expect scattered to numerous
showers to develop on Friday and Saturday (highest chance across
southeast Georgia). Heavy rainfall will be the main concern
this weekend as PWATs rise back up again to 2.0 inches. Not
surprisingly, WPC has highlighted the region in a Marginal Risk
for Excessive Rainfall on Friday and Saturday w/ the majority of
the rainfall occurring throughout Saturday. Highs will be near
normal as temperatures are expected to reach into the low to mid
90s on Thursday. However, as this cold front stalls nearby,
expect somewhat of a cool off as highs only reach into the mid
to upper 80s across SE South Carolina and low 90s across SE
Georgia. Lows will dip into the low 70s inland and then mid 70s
along the coastline.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
This aforementioned cold front could potentially stall across
the region into Sunday. A good amount of moisture will linger
along with the front and allow scattered to numerous showers and
thunderstorms to develop on Sunday. Therefore, it is possible
to see locally heavy rainfall again on Sunday as well. A deep
upper-lvl trough situated over New England will relinquish an
associated cold front across the region on Monday and allow for
an appreciable drop in dewpoints. On the backside of the frontal
passage, strong mid-lvl ridging will push into the region and
PoPs will be less an 20% on Monday and Tuesday. Temperatures
will be near and/or slightly below normal for this time of year.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
The 12z TAF period begins with an area of IFR stratus trying to
expand to the southwest and impact the terminals. So far, IFR
conditions have impacted KCHS but still mostly stayed inland of
KJZI and KSAV. We could see at least periodic IFR ceilings at
all 3 sites through mid morning, then VFR should prevail
thereafter. There will be little to no shower and thunderstorm
activity today. Winds will be strongest at KJZI where gusts
into the 15-20 knot range will be possible at times.

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

&&

.MARINE...
Today through tonight: Winds across the local waters will peak
today as Erin makes its closest passage. The strongest winds are
expected through midday with sustained winds as high as 20
knots and gusts to around 25 knots. We could even see a period
of gusts up to 30 knots in the outer GA waters. Winds will turn
more northerly by the evening and then northwesterly overnight.
Seas will peak through the period as well, thanks to powerful
swell generated by Erin. Seas are forecast to peak overnight,
with a fairly wide range of 5-13 feet, lowest across the
nearshore GA waters and highest in the outer reaches of the
Charleston County waters. Small Craft Advisories remain in
effect for all the waters outside of Charleston Harbor,
primarily for seas. We will have to watch Charleston Harbor
carefully today as there could be a period of gusts up to 25
knots.

Thursday: As the swell from Hurricane Erin finally dials back,
seas will still linger from 6 to 8 ft across the nearshore
waters and 8 to 10 ft across the outer Georgia waters. This
swell will continue to produce dangerous surf and rip currents
at all beaches. Along with the swell, strong northwesterly winds
at 15 to 20 kts with gusts up to 25 kts will be present through
most of the morning, and then switch more south-southwesterly
at 10 to 15 kts in the afternoon.

Friday through Monday: With Hurricane Erin well away from the
region, swell will continue to taper off and seas will drop out
to 3 to 4 ft in the nearshore waters and 5 to 6 ft in the outer
Georgia waters by Friday afternoon. Thereafter, seas will be
mainly be from 3 to 4 ft across all marine zones through the end
of the period. Expect east-southeasterly winds at 10 to 15 kts
through the weekend, before switching more southwesterly early
next week.

Small Craft Advisories will continue through at least Friday,
although seas should start subsiding as Erin pulls away from the
region.

Rip Currents/High Surf: The combination of elevated northeast
to north winds and impressive long period swell from Erin will
peak today along the southeast GA/SC coast. This will produce
dangerous conditions within the surf zone. A High Risk of rip
currents is in effect as well as a High Surf Advisory for large
breaking waves of 5 feet or higher, for all beaches today. All
beachgoers are urged to stay out of the water today due to these
uncommon and dangerous conditions.

Another High Risk of rip currents is expected Thursday and the
High Surf Advisory continues through Thursday evening.

&&

.TIDES/COASTAL FLOODING...
Upcoming evening high tide (~7 pm): The evening high tide is
expected to be the peak for the week as swell arriving from Erin
maximizes along with northeast winds. Tide departures have
increased over the last 6-12 hours, but there remains some
question as to how high they will get this evening. We fully
expect Charleston will peak above minor flood stage (7 ft MLLW),
with a high likelihood for moderate flooding (7.5 ft MLLW). At
Fort Pulaski, minor coastal flooding (9.5 ft MLLW) appears
likely. However, current departures need to rise over the next
6-12 hours to maximize these values. It seems likely we will
need a Coastal Flood Advisory for the entire southeast GA/SC
coast, and we could potentially issue the advisory with the next
update around 7 am.

Though winds will become less supportive and swell will
diminish, residual elevated tide levels will continue into
Thursday and Friday. Charleston could make another run for
moderate coastal flooding on Thursday, with minor likely again
Friday. At Fort Pulaski, peak tide values could be near minor
coastal flooding threshold on Thursday, but should fall short on
Friday.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...High Risk for Rip Currents through this evening for GAZ117-119-139-
     141.
     High Surf Advisory until 8 PM EDT Thursday for GAZ117-119-139-
     141.
SC...High Risk for Rip Currents through this evening for SCZ048>051.
     High Surf Advisory until 8 PM EDT Thursday for SCZ048>051.
     Coastal Flood Advisory from 5 PM this afternoon to 9 PM EDT
     this evening for SCZ049-050.
MARINE...Small Craft Advisory until 2 PM EDT Friday for AMZ350-352-354.
     Small Craft Advisory until 8 AM EDT Saturday for AMZ374.

&&

$$

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