553
FXUS62 KCHS 090929
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
529 AM EDT Wed Jul 9 2025

.SYNOPSIS...
Weak high pressure will extend across the area through the
weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
Today: Atlantic-based deep-layered subtropical ridging that has
extended west into the Southeast U.S. for the past few days
will begin to steadily erode today as a shortwave propagates
across the Great Lakes and a mid-level weakness that was over
the lower Mississippi Valley Tuesday shifts east into western
portions of the Deep South. A Tropical Upper Tropospheric Trough
(TUTT) over the Bahamas is forecast to meander a farther to the
west today which will also help to weaken and erode the southern
flanks of the subtropical ridge. The net result will be lower
mid-level heights across the Southeast U.S. and about a 1-2
degree drop in 500 hPa temperatures.

Today is shaping up to be a convectively active day. Forecast
soundings show convective temperatures have lowered quite a bit
since Tuesday with a tropical airmass, characterized by PWATS
2.15-2.30", holding across the region. The position and geometry
of the Bermuda-Azores high offshore suggests the resultant sea
breeze will form fairly early and progress steadily inland as
the afternoon progresses. The combination of lower convective
temperatures and a sharpening low-level convergence field within
the deepening sea breeze circulation should support a fairly
early (late morning/early afternoon) convective initiation
across the coastal counties. Convection will then begin to
refocus along/west of the I-95 corridor through the afternoon as
strong mixed-layer instability beneath of a plume of cooler
mid-level temperatures (-7 to -8C at 500 hPa) helps to spark
additional clusters of showers/tstms, becoming focused along
convective outflows and near other mesoscale boundary collisions.
09/01z NBM pops of 60-80% look reasonable based on the latest set of
CAMS and output from the HREF.

Similar to the past few days, shear will remain weak with
modified soundings showing an environment favorable for pulse
severe tstms. The primary hazards look to be damaging winds due
to wet microbursts as well as frequent cloud-to-ground lightning
and heavy rainfall. Quite a bit of H-CAPE (~1300 J/kg) is noted
on forecast soundings which could support some large hail as
well, but mostly likely no larger than half dollar (1.25")
size. The risk for severe tstms (especially those with hail)
looks greatest where updrafts become enhanced near/along
mesoscale boundary collisions. In addition to severe weather,
there will be a risk for isolated flash flooding. HREF
neighborhood probabilities are showing probabilities for
>3"running in the 20-30% range west of I-95. In fact, the HREF
Ensemble Localized Probability Matched Mean (LPMM) output shows
a potential for as much as 5" spots. These values certainly look
reasonable given the amount of instability, weak wind fields
and elevated PWATs that are in place. This could lead to areas
of at least minor flooding, especially of low-lying and poor
drainage areas, but pockets of mostly isolated flash flooding
could occur.

Highs today will be curtailed somewhat by the amount of
convection that is expected to form. Highs will range from the
lower 90s inland to the lower-mid 80s at the beaches. Dewpoints
will mix out again by peak heating, but likely not as much as
previous days. Some dewpoint pooling back into the mid-upper 70s
could occur near/behind the sea breeze with a few spots likely
registering an 80 dewpoint. Heat indices will generally run into the
100-105 range and well below local Heat Advisory criteria.

Tonight: Convection will gradually wind down through the night
although the risk for isolated showers/tstms will likely persist
through daybreak Thursday. Lows will range from the lower 70s
well inland to around 80 at the beaches and Downtown Charleston.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY/...
The surface pattern will feature high pressure fixed offshore
and a weak trough of low pressure across the Appalachians. A
mid-level shortwave located over the Tennessee Valley will shift
toward the Mid-Atlantic Thursday into Friday. Afterwards,
ridging aloft will begin to build back over the Southeast Friday
night and Saturday. At the least, scattered showers and
thunderstorms are possible each day through Saturday, mainly in
the afternoon and evening. Thursday looks to be the greatest
coverage with upper forcing mechanisms spreading in from the
northwest along with the usual convection initiating along the
sea breeze and other mesoscale boundaries. Friday and Saturday
show a decreasing trend in coverage due to the transition to
zonal flow then ridging aloft. Although lesser coverage, we
still anticipate at least scattered convection as there does not
appear to be any shortage in moisture (PWATs ~2.2") with west
southwesterly flow continuously advecting Gulf moisture into the
region.

A gradual warming trend will ensue through the period, thanks
to the building upper ridge, with high temperatures starting in
the upper 80s/low 90s Thursday. By Saturday, mid 90s will be
common just about everywhere except for the beaches with highs
peaking near 90 degrees. Overnight lows both Thursday and Friday
night will remain in the low/mid 70s away from the coast, and
upper 70s at the beaches.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
Ridging will continue to build over the Deep South late this
weekend and into early next week. Otherwise, little change
expected in the overall synoptic pattern and the forecast.
Typical diurnal convection will continue with scattered showers
and thunderstorms forming each day in the afternoon/evening.
Sunday will be rather hot as highs in the mid 90s could approach
the upper 90s in some areas. Heat indices could make a run for
our local Heat Advisory criteria (108 degrees), thus we will
continue to monitor in the event advisories are needed.
Thereafter, temperatures will still remain above normal, but
highs will settle back into the lower 90s.

&&

.AVIATION /10Z WEDNESDAY THROUGH SUNDAY/...
09/12z TAF Discussion:
KCHS/KJZI/KSAV: The risk for tstms impacting the terminals will
be elevated this afternoon, especially compared to the past few
days. Impacts look greatest at KCHS and KSAV roughly 18-21z.
TEMPO groups for TSRA where included during these periods to
trend. Tstms may end up just west of KJZI given an early push to
the sea breeze, but VCTS was included 17-19z given their likely
proximity to that terminal. Showers/tstms may linger near KSAV
into this evening, but data suggests it will remain concentrated
to the west of the terminal. Activity should end by late
evening with VFR prevailing at all terminals overnight.

Extended Aviation Outlook: Flight restrictions are possible
each day due to scattered showers and thunderstorms each
afternoon/evening.

&&

.MARINE...
Through Tonight: South winds will persist today, but will back
slightly with the sea breeze this afternoon. Speeds will
generally range from 10-15 kt through tonight, but will be
closer to 15 kt with gusts to 20 kt near the land/sea interface
and Charleston Harbor near and behind the sea breeze. Southwest
winds may end up higher than what the NBM is depicting for
tonight with the surface pattern favorable for deep summer
nocturnal surging. Seas will average 2-3 ft.

Thursday through Monday: A fairly typical summertime pattern
will remain in place for much of the week with Atlantic high
pressure centered offshore and a weak trough developing inland
each day. Relatively benign conditions are expected across the
local waters as a result, with south to southwest winds 15 kt or
less and seas between 2-4 ft, dropping to 2-3 ft late this
weekend. Gusts up to 20 kt are possible along the coast and in
the Charleston Harbor due to sea breeze influences each
afternoon.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.

&&

$$