452
FXUS62 KCHS 172043
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
443 PM EDT Tue Sep 17 2024

.SYNOPSIS...
Low pressure across the Carolinas will weaken through mid week.
High pressure will then develop inland late this week, and
persist into the weekend.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Tonight: Models continue to show that the closed upper low,
currently over western NC and northwest SC, will remain nearly
stationary tonight, with a slight drift east-southeast late.
Deeper moisture is expected to increase slowly through the night
as moisture on the west and southwest side of the upper low
pushes southward into the area. Some guidance is indicating a
very low chance for some showers to develop over our southern/GA
zones toward sunrise, but in collaboration with surrounding
offices, decided to leave out for now. Lows expected to fall
back into the mid to upper 60s, near to slightly below seasonal
normals.

With increasing moisture at the low and mid levels, along with
light winds and temperatures likely radiating near the surface
dewpoint temperatures, we could see some shallow/patchy fog,
but confidence not yet high enough to put in the grids.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...
Wednesday: The mid-levels will consist of a trough over the East
Coast. Embedded within it will be a Low, roughly 579 dam at 500 mb.
It`ll be located just to our northwest in the morning. But it`ll
shift to the north and elongate, becoming located over the Mid-
Atlantic States overnight. At the surface, a stationary front will
be spread over our far inland zones, or just to our west during the
day. It`ll start to transition to a cold front and move towards the
coast by daybreak Thursday. There will be a decent amount of
moisture in place with PWATs peaking around 2", which is around the
90th percentile for this time of year. Both the synoptic models and
the long-range CAMs have isolated, light showers developing over by
the late morning. By the afternoon, scattered showers are expected
across most of our area. A few rumbles of thunder are also possible.
The showers should gradually decrease as the atmosphere stabilizes
in the evening, then things dry our over land overnight. High
temperatures will be in the mid to maybe upper 80s, except cooler at
the beaches. Low temperatures will be in the upper 60s, except lower
70s at the beaches.

Thursday: A mid-level trough will be over the East Coast in the
morning. Embedded within it will be a Low located over the Mid-
Atlantic State. While the trough will stay in place, the Low will
shift towards New England. The surface stationary front will be
spread over our coast at daybreak. It`ll quickly shift offshore as
time progresses. High pressure will then form further inland. PWATs
will initially be as high as 2" in the morning. Though, they`ll
gradually trend lower as time progresses. The combination of this
moisture and lift from the front and maybe sea breeze will lead to
isolated showers along our coast in the afternoon, and scattered
shower across the Charleston Tri-County. A few rumbles of thunder
are also possible. These showers will quickly dissipate during the
evening, with it being dry overnight. High temperatures will again
be in the mid to maybe upper 80s, except cooler at the beaches. Low
temperatures will be in the mid/upper 60s, except lower 70s at the
beaches.

Friday: The mid-levels will consist of a trough over the East Coast,
with an embedded Low over or near New England. At the surface, broad
High pressure will be over roughly the mid-Appalachians. This will
usher much drier air into our region, with lower PWATs and dew
points. Expect a mostly sunny day with a bit of an increase in
clouds during the afternoon. Northeast winds will keep highs in the
low to mid 80s.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
WPC has High pressure over portions of the Southeast U.S. for much
of the long term. The NBM reflects this thinking well. Simply put,
we`ll have dry conditions with temperatures at or slightly below
normal.

&&

.AVIATION /20Z TUESDAY THROUGH SUNDAY/...
Tonight: VFR conditions are expected to prevail at all
terminals through 18z Wednesday. Some guidance showing potential
for light/shallow fog by sunrise Wednesday, but latest model
soundings look too dry to mention in TAF at this time. Have
introduced Prob30 for light showers late in the period for KSAV.

Extended Aviation Outlook: Very brief flight restrictions are
possible due to showers Wednesday and Thursday afternoon/evening.
Otherwise, VFR.

&&

.MARINE...
Tonight: No significant changes to previous forecast with no
highlights. West to southwest winds will dominate through today
before backing more southerly tonight. Wind speeds will
generally stay in the 5 to 10 knot range this afternoon and
tonight. Seas of 3 to 5 feet are anticipated rest of today,
subsiding to 2 to 4 feet tonight.

Extended Marine: Low pressure and a stationary front across the
Carolinas will weaken on Wednesday. The front should transition into
a cold front and quickly move through the waters on Thursday. High
pressure will then prevail inland Friday and persist into the
weekend. Additionally, Low pressure should be located well to our
northeast this weekend. Sustained winds will generally be 10 kt or
less Wednesday with seas 2-4 ft. Wind direction will change as the
front moves through on Thursday, while seas are 2-3 ft. Northeast
winds become more dominant starting on Friday. They may be at their
strongest each night. Regardless, both winds and seas appear to
remain just below Small Craft Advisory criteria throughout the
long term time period.

Rip Currents:
Wednesday: The combination of a lingering swell around
2 ft at 9 seconds and high astronomical tides from the full moon
will lead to a Moderate Risk of rip currents for all of our beaches.

&&

.TIDES/COASTAL FLOODING...
Latest trends and guidance indicate that tide levels for
Charleston and Colleton County coast will reach minor Coastal
Flood levels this evening. Thus, have issued a Coastal Flood
Advisory for the Charleston and Colleton coasts. Tide levels
are currently expected to peak just shy of Coastal Flood
Advisory levels for the remainder of the coast, but will
continue to monitor trends in the event an Advisory is needed
for that area too this evening.

Positive tidal anomalies along with High astronomical tides from the
full moon will lead to elevated tides for the rest of this week.
Coastal Flood Advisories will probably be needed, especially for
Charleston and coastal Colleton Counties.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...High Risk for Rip Currents until 8 PM EDT this evening for GAZ117-
     119-139-141.
SC...High Risk for Rip Currents until 8 PM EDT this evening for
     SCZ048>051.
     Coastal Flood Advisory until 10 PM EDT this evening for SCZ049-
     050.
MARINE...None.

&&

$$

NEAR TERM...RFM
SHORT TERM...
LONG TERM...
AVIATION...RFM
MARINE...RFM