020
FXUS62 KCHS 021926
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
326 PM EDT Tue Jul 2 2024

.SYNOPSIS...
A weak area of low pressure will linger across Southeast
Georgia through Wednesday. Through the rest of the week, a hot
and humid air mass will build over the region. A weak cold front
could approach the region by early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
02/18z mesoanalysis placed the stationary front just south of
the Altamaha Sound. An area of concentrated showers with
isolated tstms persists near the front, but overall, the risk
for heavy rainfall for the remainder of the afternoon has mostly
ended. The front will begin to buckle back to north across the
coastal waters overnight while a wedge of high pressure holds
over land. Increasing convergence near the front should promote
an uptick in showers and tstms over the Atlantic later tonight.
There has been a fairly consistent signal in directing the bulk
of this activity into the far southern South Carolina coast
and into the Savannah River Entrance early Wednesday morning. Pops
up to 50% were highlighted in this region to account for this.
There will also be a risk for locally heavy rainfall and minor
flooding given some pretty hefty rain amounts have been
observed here over the past 24-hours. Otherwise, 20-40% pops
were held for the coastal counties overnight with far interior
areas mostly remaining rain-free. Lows tonight will range from
the lower 70s well inland to around 80 at the beaches.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
Wednesday: A weakening stationary front or surface trough will
remain across southeast GA through the afternoon. The HREF
indicates a pool of 1500 to 2000 J/kg of CAPE will remain along
and south of the trough. At the surface, the center of a 1020 mb
high will remain off the mid-Atlantic coast, resulting in broad
east flow across the forecast area. As temperatures warm into
the upper 80s to lower 90s, a seabreeze should develop and
advance inland during the afternoon hours. Scattered to numerous
showers and thunderstorms are expected to form over the coastal
waters of GA early Wednesday morning, the convention is
expected to spread onshore generally south of the Savannah River
from midday through the afternoon.

Independence Day: A large H5 ridge will expand across the Deep
South and Southeast US region. Forecast soundings indicate a
subsidence inversion centered at H75. This inversion should
maintain at 30 to 50 J/kg of CIN through the heat of the
afternoon. In addition, PW values should remain limited to 1.5
inches across the region. As a result, the forecast will feature
dry conditions through much of the day. However, a SCHC PoPs
are possible across portions of southeast GA, and the far inland
counties of SC. Little to no QPF is expected. Given the
position of the mid-level ridge, and expected partly sunny
conditions, temperatures are forecast to peak in the mid to
upper 90s with heat index values between 100 and 105.

Friday: GFS indicates that the center of the +590 DM ridge will
remain over the Deep South. Forecast soundings indicate that
the subsidence inversion will remain centered at H75, resulting
in at least weak capping. However, given the passage of a weak
late afternoon sea breeze, isolated showers and thunderstorms
may develop during the afternoon. High temperatures should range
in the mid to upper 90s for most areas. In addition, dewpoints
along and behind the sea breeze may increase into the mid to
upper 70s, with a few spots reaching the low 80s. Heat index
values may exceed 108 in spots, especially across portions of
the SC Lowcountry.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
The mid-level pattern through the long term will be very
interesting. The ridge will generally remain across the
Southeast U.S. as a closed low associated with TC Beryl enters
the western Gulf of Mexico. To the east, GFS and ECMWF indicate
that a closed low south of Bermuda will drift toward the
Southeast coast. As a result, moisture will gradually build
across the region under the ridge, especially as the closed low
over the Atlantic approaches from the east. At the sfc, a weak
cold front will approach from the west, expected to become
nearly stationary east of the Appalachians early next week. This
pattern should support generally diurnal showers and
thunderstorms, greatest coverage expected on Monday and Tuesday.
Conditions will remain hot across the CWA, high in the mid to
upper 90s with heat index values around Heat Advisory values.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
02/18Z TAF Discussion:
KCHS/KJZI: VFR through the period. There is a chance near MVFR
cigs could develop near KJZI after midnight as shower activity
off the lower South Carolina coast tries to develop. VCSH was
highlighted at KJZI 08-14z for now.

KSAV: MVFR cigs will improve to VFR 20-21z. VFR should then
dominate through late evening. After that, the risk for MVFR
cigs will increase again as shower activity off the coast draws
closer to the coast.

Extended Aviation Outlook: Brief flight restrictions are
possible in showers and thunderstorms, mainly in the afternoon
and evening through the period.

&&

.MARINE...
Tonight: Winds continue to frequently gust 25-30 kt across South
Carolina nearshore waters and the Savannah River Entrance this
afternoon as pinched gradient conditions persist. Models have
not handled the evolution of the pinched gradient well at all
today. Given the current trends, the advisory has been extended
until 6 PM. Winds should diminish after this the front begins to
buckle north and resulting pinched gradient relaxes a bit. Seas
will diminishing to 2-4 ft through the night.

Wednesday through Sunday: Winds are forecast to remain from the
northeast on Wednesday, generally between 10 to 15 kts. Seas
will range between 2 to 3 ft. Thursday through this weekend,
south winds are forecast to remain less than 15 kts. Seas will
favor values between 2-3 ft.

&&

.TIDES/COASTAL FLOODING...
Charleston Harbor: Minor coastal flooding is likely at
Charleston Harbor this evening (606 PM) as departures remain
around +1.35 ft above astronomical (as of 215 PM). Taking a look
at the latest P- ETSS and ETSS guidance shows models running
behind at initialization with a a 0.5/ 0.7 ft anomaly needed for
correction. This is likely due to guidance not handling the
tight pressure gradient/ stalled cold front along the coast
well. Given the above, the latest forecast for Charleston Harbor
is for a 7.4 ft (minor) high tide this evening (606 PM). A
coastal flood advisory is currently in effect for Charleston and
Coastal Colleton Counties. Another round of coastal flooding is
then possible Wednesday evening as winds veer around from the
southeast.

Fort Pulaski: Tidal departures continue to hold steady this
afternoon around ~1.65 ft (as of 215 PM). Forecast guidance also
is running behind this afternoon, and this is likely due to
global guidance (which the ETSS and P-ETTS use as forcing) not
capturing the tightening gradient along the coast with multiple
offshore reporting sites observing wind gusts just shy of 30
mph. The current forecast high tide at Fort Pulaski this evening
(608 PM) is 9.5 ft (minor). As such, a coastal flood advisory
is now in effect for Beaufort, Coastal Jasper, Coastal Chatham,
Coastal Bryan, Coastal Liberty and Coastal McIntosh counties.
There is some upside potential here as the tight pressure
gradient from the stalled frontal zone remains in the region.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Coastal Flood Advisory until 8 PM EDT this evening for GAZ117-
     119-139-141.
SC...Coastal Flood Advisory until 8 PM EDT this evening for
     SCZ048>051.
MARINE...Small Craft Advisory until 6 PM EDT this evening for
     AMZ350-352.

&&

$$