568
FXUS62 KCHS 171807
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
207 PM EDT Sun Aug 17 2025

.SYNOPSIS...
Weak high pressure will build into the region early this week
as Hurricane Erin passes well offshore through the middle of
the week. A cold front could drop into the area later in the
week.

&&

.NEAR TERM /THROUGH TONIGHT/...
This Afternoon: Aloft, weak mid-lvl troughing and associated h5 vort
energy will drift across the Southeast for the rest of the day while
weak ridging persists across Florida and the Gulf. At the sfc, weak
high pressure will attempt to spill into the area within a light
north/northeasterly flow, while a front remains well south of the
local area and subtle troughing occurs across the Midlands during
peak heating. The pattern continues to support few to scattered
showers/thunderstorms across Southeast South Carolina and Southeast
Georgia through the day, although hires guidance favors a more
confined zone of precip coverage/intensity across the I-95 corridor
along and south of Walterboro and Beaufort, SC into Southeast
Georgia coastal zones. Here sfc instability strengthens (SBCAPE
~3000-3500 J/kg) as sfc temps warm into the lower 90s this
afternoon, and is supportive for a few strong thunderstorms capable
of gusty winds, frequent lightning and heavy downpours. As was the
case for yesterday, an isolated/brief severe thunderstorm can not be
ruled out mid-late afternoon across far Southern Southeast South
Carolina into Southeast Georgia, with the greatest potential south
of the I-16 corridor across Southeast Georgia where instability is
highest and the potential for thunderstorm outflow/boundary
interactions with a local sea breeze is more likely.

One caveat to stronger thunderstorms through today is thick high
clouds shifting onshore due to ongoing/morning convective activity
across the nearby Atlantic, especially across coastal zones.
However, ample moisture will reside across the coastal corridor with
PWATs in the 2.25-2.40 inch range, which remains supportive for
showers and/or thunderstorms capable of heavy downpours and at least
minor flooding issues given slow storm motion and already saturated
grounds persisting from yesterday`s convective activity. A risk for
minor/flash flooding remains along and south of Walterboro and
Beaufort, SC in Southern Southeast South Carolina and into Southeast
Georgia along/near the I-95 corridor through late day. WPC continues
to highlight these areas in a Slight Risk for Excessive Rainfall.
Flood Advisories and/or Flash Flood Warnings could eventually be
needed.

Tonight: Few to scattered showers/thunderstorms remain in the
forecast early evening, but the bulk of activity will likely wane
and/or dissipate within an hour or two post sunset. The exception
remains along the immediate Georgia coastline, where an isolated
shower/thunderstorm is possible overnight. Attention turns over to
fog potential late tonight. Winds are expected to decouple this
evening, remaining light/calm away from the coast for much of the
night. Additionally, skies should become clear/mostly clear by late
evening and persist for much of the night. These conditions along
with favorable condensation pressure deficits suggest at the least
some potential for patchy fog to develop late tonight/early morning,
especially across Southern South Carolina into Southeast Georgia
where saturated grounds remain due to rainfall received during the
past 24 hours. Overnight lows should generally range around 70
degrees inland to mid 70s near the coast.

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY/...
The forecast area will largely stay on the eastern periphery of a
mid level ridge through mid week, with occasional weak vort maxes
poised to drop through the region. At the surface, a weak boundary
is expected to sink south into the area later Monday into Monday
night, allowing high pressure to build inland thereafter for Tuesday
and Wednesday. Meanwhile, powerful Hurricane Erin will track well
off the Southeast coast (its center forecast to stay ~500 miles to
the east). Convective coverage is not expected to be particularly
high on any given day, with just isolated to scattered showers and
thunderstorms highlighted in the forecast, mainly Tuesday and
Wednesday. Temperatures will be warmest on Monday with most areas
inland of the coast peaking in mid 90s. Heat indices will stay in
the 100-105 range. Highs settle closer to normal for Tuesday and
Wednesday. Lows will average in the low to mid 70s.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
Hurricane Erin will quickly pull away from the region on Thursday.
As this occurs, a cold front will sink into the area and could
linger in the vicinity into late week or early weekend. While
isolated to perhaps scattered showers and thunderstorms are possible
Thursday, higher rain chances arrive Friday and Saturday as deep
moisture returns, and the front and mid level energy provide
potential forcing.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
CHS/JZI: TEMPO MVFR conditions are possible between 18-20Z due to
showers and/or possibly thunderstorms. Confidence is slightly higher
at the CHS terminal, where a TEMPO group has been included. VFR
conditions are then expected this evening and tonight, but there are
some indications that patchy fog could limit vsbys a few hours prior
to sunrise. Confidence is too low to include in the latest TAF
issuance. VFR conditions are then expected between 13-18Z Monday.

SAV: TEMPO MVFR conditions are possible with thunderstorms between
20-22Z this afternoon. VFR conditions should then prevail through
the evening and early overnight. Guidance suggests patchy fog
developing near the terminal for a few hours prior to daybreak. A
prevailing group with 4SM has been introduced between 08Z-13Z Monday
to account for this potential. Otherwise, VFR conditions are
expected between 13-18Z Monday.

Extended Aviation Forecast: Brief flight restrictions are possible
in afternoon showers/thunderstorms Tuesday through late week.

&&

.MARINE...
This Afternoon and Tonight: Weak high pressure across local waters
will favor wind/sea conditions that remain well below Small Craft
Advisory levels. In general, east-northeast winds will remain 10-15
kt or less today, highest near the coast where a sea breeze occurs,
then turn more directly onshore (east), but weaken to 5-10 kt during
the night. Seas will generally range between 2-3 ft.

Monday through Friday: Attention for the week will be on Hurricane
Erin passing well off the Southeast Coast. Seas will really begin
building later Monday into mid-week, potentially peaking in the 8-11
foot range later Tuesday night through Wednesday. Winds also pick up
with some marginal 25 kt gusts possible through this period. Small
Craft Advisories have been issued for all coastal waters outside of
the Charleston Harbor, largely due to seas, beginning overnight
Monday. Hazardous seas will maintain Advisories through at least
Thursday, although they will start subsiding as Erin pulls away from
the region.

Rip Currents/High Surf: A period of dangerous beach conditions is
expected this week as Hurricane Erin passes well offshore.
Increasing long period swell will result in an enhanced risk of rip
currents at all area beaches, beginning Monday and continuing
through much of the week. A Moderate Risk is in place for Monday,
with a High Risk of rip currents forecast for Tuesday. In addition,
large breaking waves are expected, and a High Surf Advisory could be
needed towards mid week.

&&

.TIDES/COASTAL FLOODING...
Increased swell and elevated winds associated with Hurricane Erin
passing well offshore could cause higher tidal levels during the
middle of the week. At least minor coastal flooding is possible with
the evening high tide cycles as early as Tuesday. Coastal Flood
Advisories could be needed.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Small Craft Advisory from 4 AM Tuesday to 8 PM EDT Thursday
     for AMZ350-352-354.
     Small Craft Advisory from midnight Monday night to 8 AM EDT
     Friday for AMZ374.

&&

$$

NEAR TERM...DPB
SHORT TERM...ETM
LONG TERM...ETM
AVIATION...DPB/ETM
MARINE...DPB/ETM