665
FXUS62 KCHS 141944
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
344 PM EDT Wed Aug 14 2024

.SYNOPSIS...
High pressure will build in from the north through late week.
Another cold front may approach the area early next week, then
remain nearby through late week.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
A deep trough extending from low pressure aloft over Nova Scotia
will cover the eastern states and western Atlantic, while a
5940-5950 meter anticyclone remains centered over the Arklatex
region. We lie near the southern apex of the trough, and within
a northwest flow that covers the entire vertical column locally
above 700 mb. The trough will also cause TC Ernesto to lift
northward to the east of the Bahamas. At the surface across the
immediate region we find a fairly strong high pressure ridge to
continue to build in, providing us with a noticeable change in
air mass. An indication of that air mass change can be seen over
the Charleston quad-county district, where many dew points are
down in the mid and upper 60s. These dew points will push
further south through the night, and will cover much of the
northern and western counties after midnight.

Through the evening there will continue to be isolated to
scattered showers and a few t-storms, mainly near and inland
from the sea breeze. The highest PoPs of 40-50% will be found in
georgia for bryan, Liberty, Long, and Mcintosh County. This is
where we find the best MLCAPE and moisture convergence, while
further north there is actually some CINH and those areas are
deeper into the drier air. As we go through the early evening
this activity will fade, and we will be rainfree by about 9 pm.
the HREF hints at a few showers developing across McIntosh
overnight. But since the vast majority of guidance shows nothing
at all, we ignored the HREF solution for now.

As the diurnal cumulus clouds diminish this evening and winds
decouple across much of the region, this will set us up for a
less warm and muggy night that we`ve grown accustomed to the
past few months. With the 1000-850 mb thickness to get down
about 1401-1407 meters by daybreak, we`re looking at min
temperatures dropping to the upper 60s and lower 70s most areas.
The exceptions will be some middle 60s in the Francis Marion
National Forest and maybe in upper Dorchester and far inland
Colleton. While the barrier islands, the Charleston-North
Charleston metro and the Savannah area will be mainly in the
middle 70s.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/...
Thursday: A mid-level wave located over the Canadian Maritimes will
wave break early Thursday and become vertically stacked. As this
occurs, the newly formed area of closed low pressure will start to
sink south as Ernesto accelerates towards Bermuda. For GA and SC,
this will allow surface high pressure to build south and west across
the coastal plain of SC and NC. PWATs are also forecast to be only
around 1.25" (or around the 10th percentile for this time of year).
1000/ 850 mb thicknesses also respond, and are also only supposed to
be around 1410 m Thursday afternoon. This will keep high
temperatures at or just below 90 degrees, with no precipitation
expected and dewpoints falling into the mid 60s.

Friday: Sunrise will likely occur with temperatures in the low to
mid 60s for most areas Friday morning along with mid 70s at area
beaches. Surface high pressure will again remain directly overhead
Friday with no precipitation expected as the region remains on the
ageostrophic convergent side of the upper level trough axis. High
temperatures on Friday look similar to Thursday as 1000/ 850 mb
thicknesses hold at 1410 m. Low temperatures Friday night into
Saturday morning do stay several degrees warmer compared to Friday
morning or near 70 degrees.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
As the weak upper ridge moves southward, an upper-level trough is
expected to pass across the Great Lakes Saturday, and push into
Southeast Canada and northern New England Sunday and Monday. A cold
front extending southward from the associated trough is
anticipated to approach the forecast area early next week. There
is potential for this low to stall nearby into mid-week before
a mid-level trough forces it offshore. Some guidance suggests
that the upper-level trough will deepen as Ernesto passes nearby
in the Atlantic off to the East. If this holds true, then it is
possible to see an increase in instability and slightly cooler
temps Sunday through Wednesday. However, the pattern should
favor more unsettled weather conditions while the front and h5
shortwave energy provide sufficient forcing across ample
moisture.

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
KCHS/KJZI/KSAV: VFR will prevail through 18Z Thursday.

The sea breeze boundary will generate isolated to scattered
SHRA and a few TSRA this afternoon and early evening. However,
coverage is less than recent days, so nothing more than VCSH is
shown at KCHS and KSAV, with no mention at KJZI. The best chance
for any brief flight restrictions would be at KSAV between 20Z
and 23Z.

Unlike the past two mornings, there doesn`t appear to be any
chance for low stratus Thursday morning as the air mass drier
than before.

Extended Aviation Outlook: VFR conditions will prevail at
CHS/JZI/SAV terminals through Saturday as surface high pressure
remains in control. Brief flight restrictions are possible early
next week to all terminals as a front brings showers/thunderstorms
to the region starting Sunday

&&

.MARINE...
Tonight: The synoptic set-up is somewhat unusual for August,
featuring a 1021 mb high centered over Pennsylvania that ridges
south to Florida and the northern Gulf of Mexico. TC Ernesto
will be found east of the Bahamas, and the resulting pressure
difference between these two systems, will create NE and E winds
of 15 or 20 kt. There will be some gusts at times approaching 25
kt, but the duration and coverage is not enough to hoist any
Small Craft Advisories. Seas within this favorable fetch will be
as high as 3-5 feet.

Thursday: Surface high pressure will center across the coastal plain
of SC/ NC on Thursday with winds out of the northeast 10 to 15 kt.
Wind gusts up to 20 kt are likely with conditions remaining below
Small Craft Advisory criteria.

Friday: Winds will slowly veer around from the east on Friday as
surface high pressure slowly nudges east. Also at this time,
Hurricane Ernesto will be approaching Bermuda with increased swell,
period, and wave height affecting all waters. Latest GFS spectral
guidance has wave period approaching 15 feet Friday afternoon with
wave heights nearing 7 ft. The wave height here is likely slightly
underdone. Waves of 6 - 8 ft are likely out 20 nm. Small Craft
Advisories might be required for all waters on Friday.

Saturday - Monday: Through the weekend, surface high pressure will
collapse as the next mid-level wave approaches the region. As this
occurs, winds will veer around from the southwest near 10 kt through
Monday. Each afternoon winds will back from the south and slightly
increase in speed as a sea breeze circulation begins. Winds will
then calm in the evening and veer around from the southwest once
again. Small Craft Advisories may still be needed on Saturday due to
swell from Ernesto, but wave heights will subside later Saturday
below criteria. No advisories will then be needed for Sunday or
Monday.

Rip Currents: There is a low risk of rip currents on Thursday as
wave heights remain around 4 ft with mainly 6 second or less period
swell. On Friday however, Ernesto will be approaching Bermuda with
13 to 15 second swell reaching the SC and GA coast. This working in
combination with onshore winds will produce a high risk of rip
currents at all area beaches.

&&

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

&&

$$

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