857
FXUS62 KCHS 211957
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
357 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/...
Rest of today: Surface high pressure remains centered across
the Piedmont of North Carolina this afternoon with a mid-level
ridge located overhead. This persistent seasonably cool and dry
weather is thanks to a quasi-stationary mid-level wave off of
the southeast coast of the United States. Temperatures have
warmed into the mid 80s today across most of the area with
dewpoints falling to the 60 degree mark.

Tonight: Surface high pressure will remain overhead with winds
quickly falling off as the PBL decouples. Temperatures will
decrease rather quickly into the mid 60s and then slowly fall
towards the 60 degree mark (especially across the rural zones).
The main question overnight remains the possibility of fog.
Crossover temperatures are right around 60 degrees, which isn`t
completely supported across the urban zones. Over the rural
areas, this is quasi- supported (at least patchy fog).

&&

.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 /19Z TUESDAY THROUGH SUNDAY/...
KCHS/KJZI: The Charleston terminals are all VFR this afternoon
with only some diurnal CU. Winds are currently out of the
northeast 5 to 10 kt with a sea breeze expected to move inland
this afternoon into evening. As this occurs, winds will veer
around from the southeast and increase in speed to around 10 kt.
Overnight, winds will quickly go calm as the PBL decouples with
temperatures falling towards the crossover temperature (upper
50s to lower 60s). Another round of patchy fog will again be
possible, but will likely hold to only KJZI and surrounding
areas outside of Charleston.

KSAV: Savannah is currently MVFR this afternoon, but will likely
go VFR very soon. Winds are currently out of the northeast
around 5 kts with a sea breeze expected to move inland this
afternoon. As this occurs, winds will veer around from the
southeast and increase in speed to around 10 kt. Overnight,
winds will quickly go calm as the PBL decouples with
temperatures falling towards the crossover temperature (upper
50s to lower 60s). Another round of patchy fog will again be
possible, but will likely hold outside the city and KSAV.

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...
Today and tonight: Surface high pressure will persist over the
Piedmont of North Carolina allowing for northeast flow over the
waters. The elevated pressure gradient has allowed for 2 to 4 ft
seas and wind gusts approaching 20 kt as times. Tonight, seas and
winds will start to diminish as high pressure slowly moves east, or
away from the region.

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.

&&

.TIDES/COASTAL FLOODING...
A coastal flood advisory is in effect for Coastal Colleton and
Charleston Counties this evening as another round of minor coastal
flooding is forecast. The current tidal anomaly is lower than
it was last night (1.6 ft vs 1.3 ft), but the astronomical is
higher (5.56 vs 5.79 ft). This will likely create a very similar
high tide this evening as compared to yesterday/ Monday evening
(7.2 ft at Charleston Harbor).

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.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...Coastal Flood Advisory until 10 PM EDT this evening for SCZ049-
     050.
MARINE...None.

&&

$$

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