545
FXUS62 KCHS 130510
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
110 AM EDT Tue Aug 13 2024

.SYNOPSIS...
A cold front will move slowly south into the area today, then
passing through on Wednesday. High pressure will build from the
north into late week, before giving way to a cold front early
next week.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Suppressed upper level heights extend down through the mid
Atlantic and into the Carolinas with some semblance of a
boundary/tight low level theta-E gradient extending from the
central SC coast into the Atlantic. Thin line of showers and
thunderstorms continue to fire along the boundary from the upper
Charleston coast into the Atlantic, and there have been a few
showers in the last hour across northern Berkeley County where
there is some residual uncapped instability remaining.

Boundary is not expected to move much through the balance of the
night and high-res guidance suggests that convection will trend
downward through the overnight hours. Will see how that goes,
but the forecast may need to have isolated pops extended through
the night.

Otherwise, a warm and muggy night is on tap (still 83 at CHS).
Lows will end up largely in the upper 70s to lower 80s with a
few middle 70s inland.

Some model guidance suggests there could be some shallow
ground fog. But given unfavorable condensation pressure deficits
and such warm grounds, no significant visibility reductions are
expected.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH THURSDAY/...
Tuesday: The region will be caught between a broad upper trough
over the mid Atlantic and Northeast states and a mid/upper
level ridge centered over the Gulf of Mexico. A surface trough
or weak backdoor front is expected to move southward toward the
area during the day. Given PWs just above 2 inches, the presence
of some upper forcing from an upper level short wave over North
Carolina, and the approaching surface trough/backdoor front,
all point toward above climo PoPs, especially for our SC zones.
Have capped PoPs in the high end chance/low end likely for now
over the northern 1/3 of the area, but they may need to be
raised. Models also show adequate deep layer shear of 35-45
knots, but instability limited due to warm mid levels. Thus,
there is only a small chance for isolated strong to severe
storms, especially within boundary interactions later in the
afternoon. Locally heavy rainfall possible, which could easily
cause ponding of water, especially in/around urbanized areas.
Highs ranging from around 90 northern 1/3 of the area to mid 90s
southern GA/Altamaha region. Convection should decrease in
coverage later Tuesday night, but kept slight chance/chance PoPs
through about midnight. Lows in the lower to mid 70s.

Wednesday and Thursday: The upper trough axis begins to shift
off the mid Atlantic coast, while a surface trough/backdoor
front continues to slowly push southward, likely reaching the
southern forecast area by late afternoon. The front is expected
to stall near or just south of our region later Wednesday and
Thursday. For Wednesday, lingering deep layer moisture and
instability, along with the potential for a weak upper shortwave
on the backside of the upper trough, will keep at least chance
PoPs for much/all of the area, especially GA zones. By Thursday,
a deep layer ridge is shown by models to build west and north
of the region, helping to push deep layer drier conditions
southward. This will translate to much lower PoPs. Have kept
slight chance for the extreme southern GA region, and below 15%
elsewhere. Would not be surprised if the entire area stays
convection free. Highs Wednesday in the upper 80s to around 90,
then mid to upper 80s Thursday, which would be a welcome few
degrees below normal if it verifies. As the drier air pushes
southward, this will help to lower our surface dewpoint
temperatures, especially by Thursday, where many will see
dewpoints in the mid to upper 60s, especially northern and
interior zones. These lower dewpoints will allow nighttime lows
to get cooler than they have been for a while, in the upper 60s
inland to the lower 70s coast Wednesday night.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
The deep layer ridge that was building from the west and
northwest in the near term is shown by global models to flatten
and push southward by later Thursday and early Friday and
another upper level trough builds into the Great Lakes Saturday,
then weakens as it moves into the northeast U.S. into Sunday.
Friday looks dry with PoPs below mention/15% as the deep layer
ridge hangs on for one more day. With more cyclonic upper level
flow Saturday and Sunday, along with increasing deep layer
moisture as the low level flow turns southerly, expect a return
to at least slight chance PoPs both days. Will continue to
monitor the potential for strong to severe storms this coming
weekend given the presence of a full latitude upper trough and
higher values of deep layer shear. High temperatures near to
slightly below normal Saturday, then a tad warmer by Sunday.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
KCHS/KJZI/KSAV: VFR tonight into early Tuesday afternoon.

Late tonight and early Tuesday there could be some shallow
ground fog around, but no reduced visibility expected at the TAF
sites.

Scattered convection will develop after 18Z at all three sites
as the interaction of the sea breeze and a weak cold front
occurs in the area. It`s too far in advance to show anything
more than VCTS at this time. But flight restrictions can occur
at times, especially at KCHS and KJZI.

Extended Aviation Outlook:

Wednesday: Additional brief flight restrictions possible at all
sites, mainly with afternoon/early evening convection.

Thursday and Friday: Less than 15% chance for convection, with
VFR expected to prevail as deep layer dry air tries to push
southward through the region.

&&

.MARINE...
Overnight: The sub-tropical ridge si suppressed across the
southern half of Florida, as a stationary front wavers just
inland over the Southeast. This will result in mainly SW winds
at 10 to 15 kt and a little gusty early on, then mainly 10 kt or
less late. There are some indications that the front could slip
into the northernmost waters late, turning winds to the NE
around daybreak. Seas will average just 2 to 3 feet throughout.

No highlights expected through the period. A weak surface
trough/backdoor front is expected to approach the waters late
Tuesday/Tuesday night, then move slowly southward, possibly
reaching the southern/GA waters Wednesday night remaining just
south of the waters through Friday before weakening. Southwest
winds 10 knots or less Tuesday and seas 2 to 3 feet, veering to
northeast from north to south beginning Tuesday night, with
northeast winds expected all waters by later Wednesday through
Friday. Winds Wednesday through Friday generally 10-15 knots
with some gusts near 20 knots possible, especially SC waters.
Seas building to 3 to 5 feet, possibly touching near 6 feet
beyond 20 nm offshore by Thursday and Friday. By Saturday, high
pressure builds briefly over the waters with lighter winds from
the south, but seas may still hang on at 3 to 5 feet.

Rip Currents: There will likely be an enhanced risk of rip
currents late this week, as swells from distant Tropical
Cyclone Ernesto impact the beaches.

&&

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

&&

$$

NEAR TERM...
SHORT TERM...RFM
LONG TERM...RFM
AVIATION...
MARINE...