970
FXUS62 KCHS 171518
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1118 AM EDT Wed Jul 17 2024

.SYNOPSIS...
High pressure will persist offshore, while a weak trough
resides inland today. A cold front will approach the region
late week and likely stall nearby, before high pressure returns
next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Thin line of beefier convection has developed in the outer
waters of South Carolina over the last few hours along a
pronounced low level convergence axis (SPC mesoanalysis) across
that region. Convection is progressing eastward away from the
coast.

Meanwhile, broader SW/W mid level flow will dominate across the
region through tonight along the southern periphery of a strong
short- wave trough digging into the Great Lakes region. Some
semblance of a sharpening surface boundary will align along the
eastern side of the Appalachians through today resulting in
increased southwesterly flow across the coastal Carolinas and
coastal Georgia.

Very warm and humid conditions persist with PWAT values in
excess of 2 inches per recent satellite total precip water
product. 12Z CHS sounding showed nearly 1500 J/Kg MLCAPE...capped
for the time being of course. But with heating, conditions will
become increasing unstable with MLCAPE values climbing to 2-3
J/Kg at peak heating, highest along the coastal corridor where
low level moisture values will again run highest. Showers and
thunderstorms will again develop across the region, likely
initially along the sea breeze as it sharpens before
progressing inland and interacting with any additional small
scale boundaries. Scattered to likely pops are still a good bet
for this afternoon into this evening.

Severe weather-wise: Similar to the last few days, well
organized severe storms are not likely with a lack of larger
scale support. But increasing DCAPE values could support strong
wind gusts with any convection this afternoon into this evening,
along with heavy rainfall.

Highs will warm into the lower-mid 90s away from the beaches
with a few upper 90s far inland, mainly across interior
Southeast Georgia. Heat indices will peak in the 105-108 range
with 100-105 at the beaches. A few instances of heat indices
108-109 can not be ruled out, but limited coverage and
durations do not support the issuance of a Heat Advisory.
Breezy conditions appear likely at the beaches this afternoon as
the sea breeze moves inland and the pressure gradient between
high pressure offshore and a sharpening lee-side trough across
the western Carolinas tightens.

Tonight: Scattered to numerous showers/tstms across the interior
will gradually weaken as the activity pushes east to the coast.
How quickly convection wanes will be dependent on how much
overturning occurs during the late afternoon hours. Pops were
capped at 40-60% (highest inland) for now, but these will
likely have to be adjusted depending how convection and its
influence on instability evolves during the afternoon. Lows
tonight will range from the lower-mid 70s across the interior to
around 80 at the beaches and Downtown Charleston.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY/...
Broad troughing will prevail over the eastern half of the
United States on Thursday and Friday, with high pressure
beginning to build into the region from the east on Saturday. At
the surface a cold front will approach the region Thursday into
Friday, likely stalling in the vicinity of the Carolinas
through Saturday. With PWATs over 2 inches as well as plentiful
instability, scattered to numerous showers and thunderstorms are
possible each afternoon, with widespread coverage forecast on
Friday. With plenty of moisture and instability, a strong to
marginally severe thunderstorm is certainly possible, as well as
the threat for heavy rainfall. With increasing precipitation
and cloud cover temperatures will likely be a degree or two less
than earlier this week, although still hot and humid. Heat
Index values are forecast to reach 104-107F each afternoon.
However, afternoon convection could inhibit temperatures from
reaching their full potential. Overnight lows are forecast to
dip into the low 70s inland and mid to upper 70s along the
coastal counties.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
High pressure aloft and at the surface will build into the
forecast area from the east into early next week. PWATs are
forecast to remain elevated along with instability. Scattered to
numerous showers and thunderstorms will be possible each
afternoon, generally due to boundary interactions and the
afternoon sea breeze. Guidance continues to be rather bullish
with PoPs through the period, so the current forecast maintains
chance to likely PoPs, still above climatology. With above
normal precipitation and increased cloud cover through the
period, temperatures are forecast to return to near normal or
even slightly below normal through the period.

&&

.AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...
17/12z TAF Discussion:
KCHS/KJZI/KSAV: The main forecast challenge for today is the
timing/coverage of tstms. Best chances for impacts this
afternoon/evening will be at KCHS and KSAV as the sea breeze
moves inland. TEMPO groups for MVFR conditions in TSRA were
maintained at both terminals, but times were adjusted slightly,
20-23z at KCHS and 21-00z at KSAV. Data now suggest tstms may
get closer to KJZI, but possibly hold just to the west, so VCTS
was introduced 20-02z for now. Convection should gradually
concentrate west of the terminals by early evening, but there
are signals decaying showers/tstms could make a run for the
coast by late evening. VCSH with some mid-level cigs were
maintained to try and account for this. Further adjustments
will be needed throughout the day as trends become more
apparent.

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

&&

.MARINE...
Today: A modest nocturnal surge over the waters will weaken a
bit as sunrise approaches. Southerly winds will diminish to
10-15 kt this morning. Winds will begin to pick up again this
afternoon as a modest sea breeze develops along the beaches and
the pressure gradient begins to tighten between high pressure
offshore and a sharpening lee-side trough over the western
Carolinas. Speeds will increase to 15-20 kt this afternoon as a
result. Frequent gusts to 25 kt appear likely over the
Charleston Habor as well as the nearshore waters from South
Santee River to Edisto Beach by mid-afternoon so Small Craft
Advisories have been posted for these waters. Seas will average
3-4 ft with a few sets as high as 5 ft.

Tonight: The gradient will remain fairly static supporting 15-20
kt all waters again tonight. Gusts to 25 kt are the most likely
over the South Santee-Edisto Beach nearshore legs, but could
extend south to include all remaining waters. It is not exactly
clear how frequent gusts to 25 kt will be south of Edisto Beach,
so a second period Small Craft Advisory was not posted. The
need for an advisory will be reevaluated later today. Seas will
build 3-5 ft.

Thursday through Sunday: High pressure will prevail across the
marine zones while a cold front approaches the inland zones.
Conditions are expected to remain below Small Craft Advisory
criteria. Generally southerly winds 10-15 knots are forecast, with
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: Gusty onshore winds along with 2 ft swell every
8-9 seconds will support a moderate risk for rip currents
today and Thursday.

&&

.CLIMATE...
Record High Minimum Temperatures:

July 17:
KCHS: 78/2023
KCXM: 82/2021
KSAV: 80/1883

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Small Craft Advisory from 2 PM this afternoon to 6 PM EDT this
     evening for AMZ330.
     Small Craft Advisory from 2 PM this afternoon to 6 AM EDT
     Thursday for AMZ350.

&&

$$