035
FXUS62 KCHS 191052
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
652 AM EDT Thu Sep 19 2024

.SYNOPSIS...
Weak high pressure will develop over the region on Thursday.
The area of high pressure is expected to gradually strengthen
through early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Early morning update: Batch of mid level cloud cover has expanded
across a good portion of the forecast area over the last few
hours, largely north of I-16. This has curtailed the development
of widespread dense fog. Skies are a bit clearer south of I-16
where there are observations of 1/2SM or less visibility. Don`t
think it rises to the level of a Dense Fog Advisory...but I
have issued a Special Weather Statement for that area addressing
the fog.

Previous discussion...
Mid-level circulation center is now across the mid-Atlantic region
with drier mid level air wrapping around the western and southern
side of the low and down through Georgia. Ill-defined boundary
(difficult to pick out with our decoupled boundary layer) appears to
stretch from the South Carolina coastal waters and into southeast
Georgia, helping to kick off convection near the Gulf Stream. A few
showers have redeveloped north of the tri-county, up near the Grand
Strand. But quiet weather dominates across the forecast area at the
moment, with fog the main concern in the early going.

Today: First off, keeping an eye on surface obs and fog development.
Several stations have dipped to 1/2SM or less visibility at
times, but low vsbys have not locked in as of yet. Suspect that
as we approach sunrise and the boundary layer begins to stir,
there may be a period of dense fog to contend with. Stay
tuned...

Meanwhile, mid-level circulation will continue to migrate toward the
New England region with its associated trough axis aligned along the
southeast coast through the day. Aforementioned surface boundary and
better moisture will likely get suppressed further south/east away
from the forecast area as northerly flow develops across the region
later this morning. But enough low level moisture to yield a few to
several hundred J/Kg of MLCAPE this afternoon particularly across
the South Carolina counties along a pinned marine layer in the
coastal corridor. Probably enough instability and low level
convergence to kick off isolated-scattered showers across the South
Carolina counties this afternoon into early evening. But given the
marginal instability, I`m inclined to not put thunder in the
forecast.

Across southeast Georgia, a bit drier along with stronger mid level
capping per forecast soundings. A few showers are not out of the
question along the coastal corridor, but plan to have a dry forecast
across the Georgia counties today.

Lastly, highs today will warm into the middle 80s for most
areas, upper 80s across the far southeast Georgia counties.

Tonight: Any diurnally driven shower activity will fade this
evening with quiet conditions dominating. Some fog will again be
possible although with lower probabilities compared to this
morning. Lows back into the middle to upper 60s...warmer along
the coast.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY/...
Friday: The area of low pressure from Thursday will be just off of
the coast of New England 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 to upper 80s with low temperatures Friday night in the
mid to upper 60s.

Saturday: Mid-level high pressure centered over southeast Texas will
continue to elongate northeast allowing heights to rise across GA
and SC. PWATs due rise to around 1.6", but mid-level lapse rates
remain poor with an inversion in place around 800 mb. This will keep
the region dry.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
Below normal precipitation and above normal temperatures are
forecast through the long term, with above average confidence for
this especially in the Sunday through Tuesday timeframe.

There have been several notable trends in the ensemble guidance over
the last couple of days, as a cornucopia of blocks persist across
the Northern Hemisphere. The main issue that ensemble guidance has
been trying to resolve the last couple of days is a Rex block that
is forecast to develop over northern Quebec. This then influences an
upper level low over the Canadian Maritimes and the southern
decaying weakness off of the Mid-Atlantic coast. The trend in the
ensemble guidance has been for the Rex Block to center further east
and allow the decaying weakness off of the Mid-Atlantic coast to
exit the region quicker. This further east Rex block also means that
temperatures and dewpoints continue to trend up for this weekend.

Sunday into Monday: Mid-level heights will start to rise across SC
and GA from a building 500 mb ridge. This will allow temperatures to
also increase into the upper 80s to low 90s inland. No precipitation
is expected as mid-level ridging builds and PWATs remain around 1.5".

Tuesday through Wednesday: 500 mb ridging looks to translate east
and center across the southeastern United States. As this occurs,
temperatures will remain seasonably warm, or above average, in the
upper 80s to low 90s. Mostly dry weather is expected, but afternoon
sea breeze convection can`t be completely ruled out as PWATs rise
towards 1.75".

&&

.AVIATION /10Z THURSDAY THROUGH MONDAY/...
19/06z TAF Discussion:
KCHS/KSAV/KJZI: A touch of fog/mist/shallow ground fog will
impact the terminals through 13Z this morning. Dense fog at the
terminals is looking less likely however, owing to a band of mid
cloud cover moving through the region. But 12Z TAF forecasts
will feature minor (MVFR) vsby restrictions until 13Z. VFR
conditions should return after 13Z with scattered to briefly
broken Cu development during the afternoon hours.

A few showers are possible across southeast South Carolina this
afternoon. Probabilities for showers to impact any one terminal
are too low to include in the forecasts.

Tonight: Some fog/mist is again possible overnight into Friday
morning producing low end MVFR visibilities.

Extended Aviation Outlook: VFR. No precipitation is expected.

&&

.MARINE...
Light and somewhat variable winds out there this morning will
give way to north/northeasterly winds 10 knots or less later
this morning and through tonight. Seas 3 feet or less.

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 through Monday: Building high pressure will result in
northeast winds 10 to 15 kt with gusts 15 to 20 kt. Seas 3 to 4 ft.
Winds and seas should remain below advisory criteria.

&&

.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.

The astronomical high tides start to lower Saturday and Sunday, 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...Coastal Flood Advisory until 11 AM EDT this morning for GAZ117-
     119-139-141.
SC...Coastal Flood Advisory until 11 AM EDT this morning for SCZ048-
     051.
     Coastal Flood Advisory until noon EDT today for SCZ049-050.
MARINE...None.

&&

$$

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