-- Discussion containing changed information from previous version are highlighted. --
390
FXUS62 KCHS 241707
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
107 PM EDT Tue Jun 24 2025

.SYNOPSIS...
High pressure will remain across the Southeast U.S. over the
next couple days, then slowly shift offshore by the end of the
week. Hot and humid conditions are expected to continue with
rain chances increasing mid to late week as surface troughing
begins to form over the region.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
Early this afternoon: No change to the forecast. Previous
discussion continues below.

Late this morning: The primary forecast issue is the heat. Low-
level thickness values from the 12z KCHS RAOB are higher than 24
hours ago as anticipated, and support highs in the upper 90s
away from the immediate coast. These temperatures, combined with
dewpoints in the upper 60s to low 70s will yield heat index
values solidly in the 105-110 degree range across the area.
Inland areas will likely see dewpoints mix out a bit more (upper
60s) and in these areas heat indices will likely fall a little
short of our explicit Heat Advisory criteria (heat index of
108-112). The areas most likely to exceed 108 heat index are
along the coastal corridor where dewpoints will sit a bit
higher, and across the entire Charleston Tri-County region.
Regardless of specific heat index criteria, it will be quite hot
and humid and supportive of the Heat Advisory that is already
in place. The other forecast issue of the day concerns afternoon
convection. The environment is slightly more supportive of
thunderstorm development, and we have kept the small area of 20
percent rain chances in the forecast. The best chances will be
across inland portions of Colleton County and the Charleston
Tri-County region.

Tonight: No significant changes are expected to the overall
pattern in regards to high pressure dominating the weather
pattern across the Southeast. Sfc winds will likely decouple
early evening, with most areas experiencing light/calm winds
away from the coast after midnight. Temps will remain mild, with
lows generally ranging in the mid-70s inland to upper
70s/around 80 closer to the coast and across Downtown
Charleston.
-- End Changed Discussion --

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
This strong upper-lvl ridge that has been sitting across the
Southeastern CONUS the last couple of days will finally begin to
break down Wednesday afternoon. According to latest model
guidance, 500MB heights on Wednesday morning will be ~594 dam,
and then weaken to ~590 by Wednesday evening. While these are
still high heights for the region, the highest heights will
continue to remain just to the north. Temperatures will climb to
the mid to upper 90s on Wednesday, with heat indices creeping
~104-106 in the afternoon. Over the last couple days, the NBM
has been overplaying temperatures and dewpoints and thus, have
adjusted the temperatures and dewpoints down a little in this
period due to these recent trends. As of right now, heat indices
remain below Heat Advisory criteria (108F), but this will
continue to be monitored. Models have been fairly consistent
with a weak surface trough forming over the Bahamas sometime on
Wednesday and then meandering across the northeastern portion of
the Gulf through the weekend. This feature will allow for some
moisture to finally return back into the region. Additionally,
SPC has placed the majority of region in a marginal risk and the
far interior South Carolina counties in a slight risk for
severe thunderstorms on Wednesday. According recent runs of the
NAM and GFS, PWAT values will be ~1.75 to 2.0 inches for
Wednesday afternoon. This will yield the chance for showers and
thunderstorms to develop in the afternoon along the seabreeze.
With strong instability ~1500-2500 J/kg, mid-lvl lapse rates
~7.5-8.0 C/km, and DCAPE values in excess of 1250 J/kg in the
afternoon, thunderstorms on Wednesday could become severe with
the main threat being damaging wind gusts.

As this weak surface trough floats nearby, the aforementioned
upper-lvl ridge will continue to weaken and eventually move
offshore by the end of the week. Therefore, a more typical
summertime pattern will set up for Thursday and Friday, with
showers and thunderstorms developing in the afternoon along the
seabreeze. Overnight lows will remain mild and only dip into the
low to mid 70s.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
This weak surface trough will meander across northeastern
portion of the Gulf before eventually dissipating sometime on
Sunday. A more zonal pattern will set up over the Southeastern
CONUS thereafter. With moisture making a full return into the
region, ensembles continue to indicate daily chances of rain
through early next week. Temperatures will remain above normal
for this time of the year.

&&

.AVIATION /17Z TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --
VFR conditions will prevail at KCHS, KJZI, and KSAV through 18z
Wednesday. Any isolated thunderstorms this afternoon are
expected to remain inland of the terminals. There is a better
chance of thunderstorms Wednesday afternoon, but likely beyond
the 18z TAF period.

Extended Aviation Outlook: VFR will mainly prevail throughout
the period, however there could be brief flight restrictions in
the afternoon hours through the end of the week as rain chances
make a return.
-- End Changed Discussion --

&&

.MARINE...
Today and Tonight: Atlantic high pressure will dominate the
pattern across local waters, favoring conditions that remain
well below Small Craft Advisory levels through tonight. In
general, a westerly offshore wind associated with a land breeze
will take place early, but sfc winds will gradually turn
southwest mid-late morning, then south this afternoon as a sea
breeze develops and pushes inland. Wind speeds should top out
around 10 kt for a bulk of the day. Winds should then turn more
southwest by mid evening, remaining around 10 kt through the
night. Seas will generally range between 1-2 ft.

Wednesday through Saturday: As a weak ESE swell continues to
mix in, seas will remain around 1 to 3 ft. Expect winds at 5 to
10 kt to prevail throughout the period. It could become a bit
gusty each afternoon with gusts up to 15 to 20 kt as the
seabreeze pushes inland (gusts strongest across the immediate
coastline and the Charleston Harbor).

&&

.TIDES/COASTAL FLOODING...
Astronomical tides will peak around 6.5 ft MLLW at Charleston
with the evening high tide cycle this evening and Wednesday
night. Afternoon winds will only be marginally supportive of
increasing tidal departures each day. The evening high tide will
likely peak around 6.8-6.9 ft MLLW each evening, falling just
short of Coastal Flood Advisory criteria.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Heat Advisory until 8 PM EDT this evening for GAZ087-088-
     099>101-114>119-138.
SC...Heat Advisory until 8 PM EDT this evening for SCZ040-042>045-
     047>052.
MARINE...None.

&&

$$

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