630
FXUS62 KCHS 181709
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
109 PM EDT Wed Sep 18 2024

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

&&

.NEAR TERM /THROUGH TONIGHT/...
Mid level low over the western Carolinas will slowly shift east
with time today. While at the surface, a weak trough/boundary
remains draped across the region. Radar early this afternoon
showed shower coverage expanding across the area. We should see
this trend continue with numerous showers and some thunderstorms
expected. High temperatures should peak in the mid 80s.

Tonight: Circulation center will be drifting northward to the
mid-Atlantic region with the stronger forcing for ascent
shifting offshore. With loss of heating, precip coverage will
diminish, although given the larger scale forcing, shower
activity might continue to percolate through the evening hours
and possibly into the overnight. Lows tonight will deep back
into the 60s.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY/...
Thursday: A vertically stacked low pressure will be located across
the eastern Mid-Atlantic Thursday morning and be slowly exiting the
coast. At the surface a remnant occluded front will be sagging south
into the Tri-County with a pronounced dry conveyor belt located over
coastal GA (as seen on RH fields). Due to this, have raised PoPs
across the TriCounty (30 - 40 %), while also keeping GA dry as 500/
300 MB RH is forecast to be only around 10%. Forecast soundings for
SC do show some instability in place (MLCAPE around 300 J/kg), but a
mid-level inversion does exist. As such, expect most of the coverage
to be shower based, with a few rumbles of thunder possible. Expect
high temperatures in the mid 80 across SC and upper 80s over GA.
This is thanks to a gradient of 1000/850 mb thicknesses with higher
values over GA (ahead of the occlusion) and slightly lower values
over SC. Low temperatures Thursday night will be in the upper 60s to
near 70.

Friday: The area of low pressure from Thursday will be just off the
coast of New England Friday with SC and GA falling on the convergent
side of the trough axis. This coupled with decreasing PWATs (down to
around 1.45") will keep the day precipitation free with surface high
pressure nudging in from the north. Expect high temperatures mostly
in the mid 80s with low temperatures Friday night in the mid
60s.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Global ensemble guidance is in very good agreement that a trough
axis will remain centered along and south of the Canadian Maritimes
this weekend with a slow translation of the wave axis east Monday
into Tuesday. This will allow for dry conditions Saturday and Sunday
with slightly above normal temperatures as surface high pressure
remains in control.

Monday into Tuesday, the long wave trough axis will move east of the
area with mid-level heights rapidly rising across the region. As
this occurs, the humidity will return to the region as well as the
chance of afternoon showers and thunderstorms (starting on
Tuesday).

&&

.AVIATION /17Z WEDNESDAY THROUGH SUNDAY/...
Prevailing VFR through 18z Thursday, although brief flight
restrictions are possible in showers and maybe a couple
thunderstorms this afternoon and evening. Shower coverage will
slowly diminish late evening and overnight. Towards Thursday
morning, there are some indications that fog/low clouds could
develop. Showed hints of this in the TAF but did not have high
enough confidence to include prevailing restrictions.

Extended Aviation Outlook:
Thursday: Morning MVFR cigs possible with prevailing VFR in the
afternoon. A few afternoon showers and thunderstorms are
possible which could temporarily restrict cigs and vsbys. A weak
boundary will cross the terminals Thursday turning the winds
from the northeast.

Friday through Sunday: VFR. No precipitation is expected.

&&

.MARINE...
Southerly winds around 10 knots will prevail across the coastal
waters through tonight with seas running 2 to 4 feet.

Thursday: Another round of morning showers and thunderstorms are
possible with a weak boundary crossing the waters Thursday. Winds
will turn from the northeast 5 to 10 kt. Seas 2 to 4 ft.

Friday: Northeast winds will slowly start to increase in speed 10 to
15 kt as surface high pressure builds in from the north. Wind gusts
of 15 to 20 kt possible, or below Small Craft Advisory criteria.
Seas 3 to 4 ft.

Saturday and Sunday: Northeast winds 10 to 20 kt with gusts 15 to 25
kt. Seas around 4 ft. A Small Craft Advisory might be required as
the pressure gradient tightens from building high pressure.

Rip Currents: 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
today.

&&

.TIDES/COASTAL FLOODING...
Positive tidal anomalies along with high astronomical tides from the
full moon will lead to elevated tides for the rest of this week and
through the weekend. Coastal Flood Advisories will probably be
needed for both the morning and evening high tides through Friday
for both Charleston Harbor and Fort Pulaski.

Saturday and Sunday, the astronomical high tides start to lower but
the morning high tides will likely be elevated enough to still
require Coastal Flood Advisories (especially for Charleston and
coastal Colleton Counties). More uncertainty exists for Fort
Pulaski.

&&

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

&&

$$

NEAR TERM...ETM
SHORT TERM...Haines
LONG TERM...Haines
AVIATION...ETM/Haines
MARINE...Adam/Haines