398
FXUS62 KCHS 131809
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
209 PM EDT Sat Jul 13 2024

.SYNOPSIS...
A weak front will meander across the area today. Atlantic high
pressure will then rebuild across the area while a surface
trough exists inland Sunday through the middle of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
This Afternoon: Aloft, a mid-lvl ridge will persist across the
Southeast United States. At the sfc, weak low pressure will meander
across Southeast Georgia with a subtle trough extending north across
the eastern portions of the Carolinas. The pattern will favor a
slightly weaker onshore wind compared to the previous day, but will
continue to advect moisture characterized by PWATs in excess of 2.0
inches across a large portion of the area. An afternoon sea breeze
interacting with the nearby front/boundary will remain the primary
zone for strongest moisture convergence resulting in scattered to
numerous showers/thunderstorms along and east of the I-95 corridor
and particularly across the Tri-County Area. Here, strong instability
characterized by SBCAPE between 3500-4000 J/kg, PWATs near 2.25
inches and slow storm motion support greatest convective coverage
and the potential for a few thunderstorms to produce a quick
1-2 inches of rainfall away from the coast mid to late afternoon.

Outside/before precip, warm and humid conditions are in place with
many areas expected to see heat index values up to 105-107 degrees.
A few locations that see precip late could briefly see heat index
values above 108 degrees, especially south of Charleston County near
the coast where sfc dewpts are less likely to mix out compared to
inland areas. For areas well inland where high temps approach the
mid-upper 90s, sfc dewpts will likely mix out into the mid-upper 60s
by mid afternoon. Given expected precip and low-lvl mixing limiting
the spatial coverage and duration of higher heat index values, a
Heat Advisory is not anticipated across the area at this time.

Tonight: Convection will quickly wane this evening with the loss of
insolation. Expect a mostly dry night with continued warm and humid
conditions. Lows will range from the mid 70s well inland to the
lower 80s at the beaches and Downtown Charleston.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY/...
Weak ridging aloft will persist across the local forecast area
as a mid-level trough swings across the eastern CONUS. At the
surface a weak, stalled front will persist just inland of the
local forecast area. Shortwave energy will ripple across the
southern periphery of the mid-level troughing, likely remaining
to the north of the local forecast area. PWATs are forecast to
be around or just over 2 inches. Weak forcing from the nearby
front as well as local enhancements from the sea-breeze
circulation will create scattered to numerous showers and
thunderstorms each afternoon. MLCAPE values are forecast to be
upwards of 2,000 J/kg each afternoon, however with little to no
shear the threat for organized severe thunderstorms is low.
However, a strong to marginally severe thunderstorm cannot be
ruled out.

The main forecast highlight for the short term period is the
increasing heat. Hot and humid conditions are forecast each day,
with Heat Indices reaching to around 105-110 Sunday through
Tuesday. Heat Advisories will likely be required for portions of
the forecast area, mainly along and east of I-95.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
Ridging aloft will begin to retreat as a mid-level trough
swings towards the East Coast late in the week. At the surface
high pressure will briefly build into the region, with a cold
front approaching late week. At least scattered showers and
thunderstorms will be possible each afternoon, typical of a
summerlike pattern. Outside of precipitation, hot and humid
conditions are expected again on Wednesday. Another Heat
Advisory will be possible on Wednesday. Temperatures and dew
points begin to decrease Thursday and into Friday as a cold
front approaches.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
KCHS/KJZI: Prevailing VFR conditions are expected through 18Z
Sunday. However, at least TEMPO MVFR and possibly IFR conditions are
possible between 18-20Z for ongoing showers and thunderstorms near
an active sea breeze circulation and nearby/weak front (especially
at CHS). Winds become light and variable overnight, then from the
southwest under 10 kt late Sunday morning. A few showers and
thunderstorms could impact the terminals Sunday afternoon, but
confidence in timing and occurrence are too low to include in the
latest TAF issuance.

KSAV: Prevailing VFR conditions are expected through 18Z Sunday.
However, TEMPO MVFR conditions are possible between 18-20Z due to
showers and thunderstorms developing near an inland moving sea
breeze and/or boundary interactions with ongoing convection. Winds
become light and variable overnight, then from the southwest under
10 kt late Sunday morning. A few showers and thunderstorms could
impact the terminal Sunday afternoon, but confidence in timing and
occurrence are too low to include in the latest TAF issuance.

Extended Aviation Outlook: Scattered afternoon showers/tstorms
could produce brief flight restrictions at all terminals through
next week.

&&

.MARINE...
This Afternoon and Tonight: A weak pressure gradient will
prevail across local waters between dissipating low pressure
inland and high pressure extending across the western Atlantic.
Southerly winds will remain 15 kt or less, strongest this
afternoon near the coast while a sea breeze shifts inland. Seas
will range between 2-4 ft.

Sunday through Wednesday: A pinched gradient could develop over
the marine waters through early next week as high pressure
persists offshore and a trough lingers inland. However,
conditions are expected to remain below Small Craft Advisory
criteria. Generally S winds are forecast, 10-15 knots. Slightly
stronger wind speeds are possible along the direct coastline in
association with the afternoon sea breeze. Seas should average 3
to 4 ft.

Rip Currents: A moderate risk for rip currents is in place for
the Charleston County beaches today where winds will be a bit
higher compared to the rest of the coast from Edisto Beach
south. 2-3 ft swells with periods of 7-8 seconds will persist.

&&

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

&&

$$

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