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102
FXUS62 KCHS 220251
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1051 PM EDT Tue May 21 2024

.SYNOPSIS...
High pressure will persist into late week. Diurnal convection
is expected during the weekend. A cold front might approach
early next week.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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Tonight: Sfc high pressure will prevail across the region under a
ridge axis aloft, favoring a strong radiational cooling setup with
light/calm winds in place under clear skies. The main issue
overnight will be the potential for fog developing late. Crossover
temps are right around 60 degrees, which should be met across rural
areas a few hours prior to daybreak. Patchy to areas of fog remain
in the forecast late, mainly for locations along/west of the I-95
corridor and closer to the coast across the Francis Marion Forest.
Low temps should range in the upper 50s/lower 60s inland to mid-
upper 60s closer to the coast.
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&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...
Wednesday: A cut off low about halfway between Florida and Bermuda
lifts northeast, as a ridge extending from an anticyclone in the
western Gulf of Mexico stretches across the local area. While there
could be the formation of a weak lee side trough, high pressure at
the surface off the coast will be the main feature. The lack of
moisture and a continued subsidence inversion will maintain its
hold, so even though a weak short wave could brush nearby late, no
risk of any convection. 850 mb temperatures reach 15-16C, and that
along with an expansion of the low level thickness will support max
temperatures in the mid and upper 80s away from the beaches.

Wednesday night: Winds decouple in the evening, leading to another
night with good radiational cooling. We leaned toward the cooler
side of guidance as a result. Although there is another day of
drying in the boundary layer, guidance insists that fog can again
develop within a southerly synoptic flow. We added mention of
patchy fog to the forecast.

Thursday: The axis of the ridge aloft pulls east and gives way to
more of a zonal flow, while at the surface the gradient does tighten
some between Atlantic high pressure and a lee side trough. TRhere`s
another short wave that could move through, and with less subsidence
and a much greater supply of moisture (Pwat up near 1.5 inches),
it`s possible the sea breeze could try and initiate some showers and
t-storms. For now we keep it rainfree. 850 mb temperatures climb
another degree C, so we added a couple of degrees to max values,
which will hit 90F most places away from the shoreline. A warmer
night with higher dew points.

Friday: The flow aloft will be mainly zonal, with a decent short
wave moving through the Ohio Valley. At the surface, Atlantic high
pressure is again the main feature, with a lee side trough possible.
The sea breeze again looks to be the main mechanism for any
convection that might occur, as well as the upstream trough. So
perhaps a few t-storms pop in the afternoon. Both the low level
thickness and the 850 mb temperatures climb even more, so we added
highs another 1-2F.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
A weak trough should pass to our north Friday night into early
Saturday, followed by zonal flow over the Southeast through Monday,
with indications of a trough moving closer by on Tuesday. Surface
high pressure will remain in the western Atlantic while fronts are
forecasted to pass to our north. Expect convection along/near the
sea breeze each afternoon/evening, decreasing during the overnight
hours, maybe increasing in coverage Tuesday, dependent upon how far
south the cold front can get. Temperatures will remain a few degrees
above normal each day and night.

&&

.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
VFR conditions will prevail at CHS/JZI/SAV terminals through the
first half the night, but at least tempo MVFR vsbys are possible
between the 09-12Z Wednesday time frame as patchy/shallow ground fog
develops near the terminals. VFR conditions should then return
around 12-13Z Wednesday through 00Z Thursday.

Extended Aviation Outlook: Mainly VFR. Brief flight restrictions
are possible late Wednesday night/early Thursday due to fog, and
again in SHRA/TSRA Saturday and Sunday afternoon.

&&

.MARINE...
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Tonight: Very subtle coastal troughing along the southern edge
of high pressure extending across the region will lead to a few
showers across offshore Georgia waters this evening. Otherwise,
expect east-northeast winds around 10-15 kt to gradually diminish
to 5-10 kt as the pressure gradient relaxes across local waters
for much of the night. Seas will also slowly subside to 1-3 ft
across nearshore waters to 3-4 ft across offshore Georgia waters.

Extended Marine: High pressure remains the main synoptic feature
through the weekend, with the likely formation of a lee side
trough. Otherwise, expect a typical summerlike wind pattern
beginning Thursday. That`s when each day the winds will back and
be stronger along the land/sea interface with the formation of
the afternoon breeze. Gusts could approach 20 kt in the
Charleston Harbor with the passage of the sea breeze. Each
night, winds should veer as the low level jet sets up along the
coast. But no Small Craft Advisories are anticipated. Eventually
convection should return, especially this weekend.

Rip Currents: Given the astronomical influences of the Full Moon, it
won`t take more than a small swell to lead to an enhanced risk of
rip currents at the local beaches. Both the in-house Rip Current
Calculator and the Rip Current MOS point to a Low Risk Wednesday.
But if the swell is higher than anticipated, then the risk will need
to be raised. Conditions look better for an elevated risk on
Thursday with a little more wind and swell energy.
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&&

.TIDES/COASTAL FLOODING...
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Minor flooding is possible with the evening high tides Wednesday
and Thursday along coastal Charleston and coastal Colleton
Counties. There are no concerns at this time along the remainder
of our coast.
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&&

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

$$

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