040
FXUS62 KCHS 142334
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
734 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/...
Early this evening: Radar imagery shows mostly scattered shower
activity continues across southeast Georgia and along the
Savannah River in southeast South Carolina. Instability is weak,
mostly 500-1,000 J/kg of MLCAPE, and we haven`t seen any
lightning activity at all. The main thing driving additional
shower activity is the progression of outflow boundaries
creating some low-level convergence. Shower activity will
steadily dissipate over the next hour or two with the loss of
heating, and the rest of the overnight is expected to be dry. A
few hi-res solutions hint that there could be some shower
activity along the Georgia coast late tonight, but this has been
discounted due to drier air and lower precipitable water values
that are poised to spread in from the northeast overnight. We
expect to see some of the coolest lows we have seen in a while
with widespread upper 60s inland tonight. We could even see a
few mid 60s in the typical cool spots.

&&

.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 /00Z THURSDAY THROUGH MONDAY/...
VFR conditions are expected to prevail at KCHS, KJZI, and KSAV
through 18z Thursday.

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 and
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...BSH
SHORT TERM...Haines
LONG TERM...Dennis
AVIATION...BSH/Haines
MARINE...Haines