363
FXUS62 KCHS 212320
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
720 PM EDT Fri Aug 21 2026

.WHAT HAS CHANGED...
The Heat Advisory has been cancelled. Saturday will be another
hot and humid day, but should be more typical of late August
with high temperatures only a degree or two above normal in the
low to mid 90s. Dewpoints will remain elevated in the mid to
upper 70s along the coast, and the result is expected to be heat
indices more commonly in the 100-105 degree range across the
forecast area. There could be a small area along the immediate
coast that could briefly rise to around 108 degrees, but at this
time we do not anticipate sufficient areal or temporal coverage
to warrant any Heat Advisories.

&&

.KEY MESSAGES...
- 1) Strong to severe thunderstorms possible this afternoon. An
  increased risk for showers and thunderstorms will continue
  through Saturday.

&&

.DISCUSSION...
KEY MESSAGE 1: Strong to severe thunderstorms possible this
afternoon. An increased risk for showers and thunderstorms will
continue through Saturday.

Rest of Today: The ridging aloft that has been driving the hot and
humid conditions this last week has been replaced by troughing along
the east coast. A shortwave trough will ripple across the southern
periphery of the large scale troughing this afternoon and into
tonight. At the surface a cold front will approach the region from
the W/NW. Scattered to widespread convection is expected this
afternoon as the nearby front aids the sea breeze as an extra
forcing mechanism. CAMs are not in great agreement with the overall
picture of this afternoon and the current forecast features the pure
NBM as it appears to be a good middle ground amongst the suite of
guidance. Isolated convection is forecast to fire along the sea
breeze this afternoon with additional storms forming upstream across
the SC Upstate/SC Midlands. These additional storms will then
progress towards the local forecast area around sunset this evening.
Given the hot and humid airmass strong to severe thunderstorms are
possible with any storm that is able to form. SPC Mesoanalysis shows
that there is roughly 1500 J/kg of ML CAPE across the forecast area
as of noon. This is forecast to increase to around 2000 J/kg by this
afternoon. DCAPE values are also forecast to reach upwards of 1000
J/kg. Therefore, damaging wind gusts are the main hazards with any
strong/severe storm. Additionally, there is a threat of heavy
rainfall with any storm as storm motion will be slow. The 12Z KCHS
RAOB sounding had a PWAT of 2.19", which is above the 90th
percentile according to SPC Climatology.

The boundary from Friday should be positioned nearly right across
the forecast area to begin Saturday. The biggest change should come
in the depth of available moisture as drier mid and upper level air
begins to infiltrate from the west throughout the day. In fact, some
model guidance suggests that precipitable water values will fall to
less than 1.5 inches across our far inland tier of counties while
values up to 2 inches persist along the coastal corridor. There is
decent agreement among the hi-res models and the HREF that the best
convective coverage should occur along and east of I-95 with
development beginning by around midday. Model soundings aren`t don`t
suggest a particularly high severe weather threat, but there could
still be an isolated strong to marginally severe storm where
boundary interactions enhance updraft strength. Instead, there could
be more a locally heavy rainfall threat, primarily from the
Charleston metro area and to the northeast.

Sunday Onward: The aforementioned drier air should spread across the
area Sunday into Monday and yield little to no convection at all.
However, this should begin to recover starting Tuesday and into the
middle of the week with a return to more typical diurnal convective
coverage.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
22/00z TAFs:
KCHS/KJZI: Convection to the west is expected to remain west of
the terminals this evening. As an impulse moves up the coast
late, another round of showers/tstms could develop along the
lower South Carolian coast and impact the terminals. Confidence
in this scenario is only modest at best and details are
uncertain. PROB30 groups for tstms were included 07-10z at both
KCHS and KJZI to account for this. Another round of shower/tstms
could bring impacts during the late afternoon. PROB30 groups for
TSRA were included 21-00z to trend.

KSAV: Convection to the west is expected to weak as it
approached the terminal through 03z. While impacts are possible,
current trends suggest most of this should remain to the north.
A last minute change may be needed prior to issuance time.
Another round of shower/tstms could bring impacts during the
late afternoon. PROB30 groups for TSRA were included 21-00z to
trend.

Extended Aviation Outlook: Thunderstorms will again be a
concern Saturday afternoon and evening. Otherwise, VFR
conditions will prevail.

&&

.MARINE...
Rest of Today: No significant marine concerns are expected
across the local waters through today, with winds and seas
remaining below Small Craft Advisory criteria. A typical
summertime pattern will dominate with generally south-
southwesterly flow around 10 kt and seas 2-3 ft.

Saturday through Wednesday: Saturday could bring a period of
modestly stronger southwest flow late in the day and into the
evening, though wind speeds should top out in the 15-20 knot
range. Perhaps the main concern for Saturday will be
thunderstorms which are expected to develop along the coast and
move out into the coastal waters, potentially producing strong
wind gusts and frequent lightning. Thereafter, conditions look
pretty typical of summer and should remain well below Small
Craft Advisory thresholds through mid week.

&&

.CLIMATE...
Record High Minimum Temperatures:

August 21:
KCHS: 79/2010
KCXM: 82/2023
KSAV: 80/1902

August 24:
KCHS: 76/2010

August 25:
KCHS: 77/1982

&&

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

&&

$$