683
FXUS62 KCHS 230830
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
430 AM EDT Mon Sep 23 2024

.SYNOPSIS...
High pressure will linger across the region until mid week. A
tropical cyclone is forecast to move generally northward across
the Gulf of Mexico, then possibly tracking inland across
portions of the Deep South or Southeast U.S. later this week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Today: Aloft, a ridge centered across the northwestern Gulf of
Mexico and extending across the Deep South and Southeast United
States will slowly nudge east as a trough advances across the
Central United States. At the sfc, weak high pressure will linger
locally this morning into early afternoon while weak low pressure
placed across the Midlands gradually drifts east and into western
most zones late day into early evening. Weak h5 shortwave energy
rippling along the northwest periphery of the mid-lvl ridge will
eventually traverse the local area, spawning a few showers and/or
thunderstorms across far inland areas late day where SBCAPE
approaches 1000-1500 J/kg. Convection will struggle somewhat with a
downslope wind aloft, but the flow is weaker and moisture levels
(PWAT near 2.0 inches) are higher than conditions yesterday under a
similar pattern, so there should be a slight uptick in precip
coverage late day into early evening. Temps should also be a degree
or two warmer than the previous day with the mid-upper lvl ridge
shifting closer to the region. In general, highs should range in the
lower 90s away from the coast, although a few locations could peak
in the mid 90s across far interior locations of Southeast Georgia
and Southeast South Carolina. Closer to the coast, high temps will
be a bit cooler (low-mid 80s) due to onshore flow and sea breeze
shifting inland during the afternoon.

Tonight: A few showers could linger across inland areas into early
evening, but expect activity to slowly diminish with the loss of
daytime heating. By around midnight, most areas should be dry. Weak
sfc high pressure should linger through the night while mid-lvl
ridging prevails aloft. Low temps should also remain a degree or two
warmer than the previous night with light southerly winds and some
clouds persisting locally. In general, lows should range in the low-
mid 70s, warmest near the beaches.

&&

.SHORT TERM /TUESDAY THROUGH THURSDAY/...
Tuesday and Wednesday: An upper ridge will traverse eastward across
the Florida Peninsula Tuesday and shift over the Atlantic by
Wednesday, meanwhile an amplifying upper trough across the Midwest
digs into the Ark-La-Tex region. Surface high pressure anchored over
northern Maine and extending southward along the Eastern Seaboard
will persist, in addition to a developing tropical system in the
Gulf of Mexico. A subsidence inversion around the 600-550mb layer
noted via model soundings will limit convection, resulting in mostly
quiet weather both days. Deep dry air aloft with some moisture
trapped in the lower levels will result in a few low clouds with
sunshine Tuesday. There are some indications within the models that
show spotty light showers far inland Tuesday, due to weak shortwave
impulses aloft. However, low cloud tops indicate any showers that
may develop should be brief with little measurable rainfall. We will
continue with no mentionable rain chances for most areas with low-
end slight chance (15%) POPs across northern Dorchester and Berkeley
counties. Increasing cloud coverage will occur Wednesday as the
tropical system and upper trough nears.

Temperatures will be relatively mild Tuesday due to the ridge aloft,
the forecast features highs in the upper 80s/low 90s. Wednesday will
be a bit cooler with highs in the mid to upper 80s owing to
increasing clouds. Tuesday night will feature lows around 70 degrees
inland and low/mid 70s along the coast with some radiational cooling
influence. Wednesday night will be warmer in the low to mid 70s
for most locations, as clouds thicken overnight.

Thursday: We turn attention to the tropical system that guidance has
been alluding to for several previous runs. Specific details will
depend on the eventual track and intensity of the system. Based on
the collaborated low position per WPC and model guidance trends, the
tropical cyclone is progged to track in a general northward
direction across the Gulf of Mexico and make landfall along the Gulf
Coast, somewhere between the AL/MS coast to the Florida Big Bend.
The proximity of the low will result in increasing rainfall
potential and gusty conditions across the forecast area. We
currently show rain spreading in the from south/southwest Thursday
with POPs ranging 40-55%. Temperatures will be cooler with overcast
skies and rains, topping out in the low to mid 80s.

&&

.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
Concern is increasing for impactful weather Thursday night into
Friday, with the potential for a rainband associated with the
tropical system to lifting northward across the region. This band
could bring rounds of heavy rainfall, gusty winds, and the potential
risk for tornadoes. Again, much will depend on the eventual track,
forward speed, and intensity of the system.

The forecast is even more uncertain for the weekend. It is possible
that dry air could wrap around the central CONUS closed low and
bring drier conditions to the region. Some guidance indicates that a
CAD may develop over the region, with rain, thick cloud cover and
cool NE winds. The forecast will keep scattered convection with
highs in the 80s trending cooler late weekend.

&&

.AVIATION /09Z MONDAY THROUGH FRIDAY/...
VFR conditions are expected to prevail at CHS/JZI/SAV terminals
through 06Z Tuesday.

Extended Aviation Outlook: VFR conditions expected to prevail
through Wednesday. Gusty conditions are possible at the terminals
during the end of the week. Potential for periodic flight
restrictions are increasing.

&&

.MARINE...
Today and Tonight: A weak pressure gradient will prevail across
local waters between broad high pressure over the western Atlantic
and weak low pressure well inland. In general, southwest winds
between 5-10 kt will become south while a sea breeze develops along
the coast, then shifts inland during the afternoon. Seas will range
between 1-2 ft across nearshore waters and 2-3 ft across offshore
Georgia waters today, then slowly build about 1 foot during the night.

Tuesday and Wednesday: Weak, broad high pressure offshore will
result in southeast winds around 10 kt. Seas will average 2-3 ft for
the nearshore waters out 20 nm and 3-4 ft for the outer GA waters
from 20-60 nm.

Wednesday night through Saturday: Winds and seas are progged to
increase/build Wednesday night due to a tropical system that is
expected to develop in the Gulf of Mexico. Details still need to be
fine tuned as much will hinge on the eventual track and intensity of
the system. Regardless, the pressure gradient across the local
waters will support wind gusts reaching Small Craft Advisory
criteria (25 kt or greater) across all marine zones with the chance
for gales Thursday into Friday. Seas could peak around 6-10 feet in
the nearshore waters out to 20 nm and 11 ft or higher in the
offshore Georgia waters from 20-60nm. Conditions look to improve
near the end of the period.

High Surf and Rip Currents: Five foot breakers are possible at the
beaches Thursday night. Additionally, an elevated risk for rip
currents is likely Thursday and Friday with gusty winds, large
breakers, and long period (10 second) swells.

&&

.TIDES/COASTAL FLOODING...
For today, a Coastal Flood Advisory will likely be needed during the
afternoon high tide cycle along Charleston and Colleton County
coasts with minor flooding expected with 1-2 hours of high tide,
which occurs around 1:10 PM.

Positive tidal anomalies and high astronomical tides from the recent
full moon will lead to elevated tides through the first half of the
week. Although the astronomical high tides are lowering, minor
coastal flooding is expected with the daytime high tide cycle along
the Charleston and Colleton County coasts Tuesday, and potentially
Wednesday.

&&

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

&&

$$

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