177
FXUS62 KCHS 211117
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
717 AM EDT Fri Aug 21 2026

.WHAT HAS CHANGED...
Aviation section updated to represent the 12Z TAF.

&&

.KEY MESSAGES...
- 1) Heat remains a concern into Friday.

- 2) Increased risk for showers and thunderstorms into the
  weekend.

&&

.DISCUSSION...
KEY MESSAGE 1: Hot and humid conditions will persist today.

Today should be the final day in this extended stretch of dangerous
heat. High temperatures will peak back up in the mid to upper 90s,
with heat indices of 105-110F. The highest heat indices will occur
closest to the coast where a Heat Advisory has been issued. There
will be convection developing in the afternoon, however it looks to
be late enough where these areas look to reach 108+ for at least a
couple of hours. No additional heat headlines are expected over the
weekend as a mid level trough and associated surface front shifts
into the region. Heat indices should generally remain below 105.



KEY MESSAGE 2: Increased risk for showers and thunderstorms
into the weekend.

Friday: A more appreciable change in the pattern is expected on
Friday as this mid-lvl ridge finally breaks down and broad
troughing begins to build across the eastern half of the CONUS.
Several embedded shortwaves are forecast to round the base of
this trough while a slow-moving surface front approaches the
region from the west and northwest. Coverage is expected to
increase this afternoon compared to the past few days as a
surface boundary slowly inches into the area. PWAT values are
expected to rise above 2 inches (near the 90th percentile for
late August at KCHS). With deep moisture rich profiles and
plenty of surface heating instability values are expected to
climb into the 1500 to 2000 Joules of MLCAPE which is more than
sufficient for deep convection. Albeit shear is paltry at best,
the influences of the upper shortwave trough should be enough to
get widespread storms mainly across and west of I-95 with some
multi-cellular clusters possible. Depending on how hot we get
during the afternoon, surface dewpoint depressions look to range
around 20 to 25 degrees and DCAPE values around 1000 to 1200
J/kg which could be supportive of damaging wind gusts with any
storms that cluster up. This threat is also supported within
some of the machine learning guidance showing a higher risk of
damaging winds along and west of I-95 during the afternoon. As a
result that portion of the area has been upgraded to a
Slight(level 2 of 5) risk for severe weather with a Marginal
(level 1 of 5) for the remainder of the area.

Saturday: The boundary looks to stall along or near the I-95
corridor allowing for another day of rather widespread coverage
as the next shortwave overspreads the area. Scattered showers
and storms look to begin throughout much of the day as subtle
height falls/ascent continue over the area. This will likely
keep temperatures a few degrees cooler than Friday; however, we
should be able to muster up enough instability to support a more
widespread round of thunderstorms during the late afternoon.
Current guidance supports a little more focus over the tri
county areas Saturday afternoon. The good news is that with the
increased cloud cover and limited instability on Saturday, the
severe risk might be a bit more marginal at best. While a strong
to severe damaging wind gust cannot be ruled out, the
probability of this occurring is certainly lower on Saturday
than Friday. The bigger issue may become heavy rainfall as slow
moving storms moving over some poor drainage areas of metro
Charleston certainly raises an eyebrow. We will continue to keep
an eye on this potential as confidence increases.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
21/12z TAFs: VFR conditions should prevail for much of the
period with light southwesterly winds becoming southerly during
the afternoon with the passage of the sea breeze. Scattered to
numerous showers and thunderstorms will likely develop after 18z
leading to possible reductions in vsbys and ceilings at all
area terminals. PROB30s were introduced after 18z to account for
this and depending on confidence in timing and coverage TEMPOs
may be needed. Continued showers and storms will be possible
along the coast around JZI and CHS during the overnight hours as
winds become more southwesterly once again.

Extended Aviation Outlook: A front in our vicinity will bring
showers and thunderstorms Saturday and Sunday, leading to
occasional flight restrictions.

&&

.MARINE...
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 Tuesday: Outside of showers and thunderstorms,
overall marine conditions will remain fairly typical for late
summer, with south-southwesterly winds generally 5-15 kt with
seas ranging from 2-4 ft through early next week. The main
concern for mariners will be the increasing thunderstorm threat
through the weekend as a front approaches and then stalls
nearby.

&&

.CLIMATE...
Record High Temperatures:

August 21:
KSAV: 101/1902


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...Heat Advisory from 11 AM this morning to 8 PM EDT this evening
     for GAZ137-216>219-238>241.
SC...Heat Advisory from 11 AM this morning to 8 PM EDT this evening
     for SCZ148>152.
MARINE...None.

&&

$$

Black/ETM