704
FXUS62 KCHS 201120
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
720 AM EDT Sat Jul 20 2024

.SYNOPSIS...
High pressure will remain over the western Atlantic while a
surface trough lingers inland.

&&

.NEAR TERM /THROUGH TONIGHT/...
early on, there will be some fog and areas of low stratus due
to the wet grounds, light winds, and near 100% relative humidity
through 8 or 9 am. The greatest potential for fog is far inland
where the more favorable condensation pressure deficits will
occur. However, given the warm grounds, no significant
visibility concerns will transpire.

The large scale pattern today reveals a broad trough aloft
covering much of the central states, with the sub-tropical
Atlantic ridge across Florida and into the Gulf of Mexico. The
result is for a continued very moist southwesterly flow across
the entire forecast district, with PWat as high as 2.0 to 2.25
inches. At the surface, the Bermuda-Azores High is in a similar
position to the ridging aloft, while trough will persist inland.

There could be just enough low level convergence to generate
a few showers brushing parts of the coastal counties this
morning. Otherwise, no convection is expected until this
afternoon with NVA and modest capping in place when we achieve
our convective temperatures in the mid and upper 80s. Forcing
will also transpire the second part of the day as a short wave
approaches, and the right entrance region of 45-55 kt upper jet
moves across parts of the Southeast. This will lead to the
formation of scattered and numerous showers and t-storms after
about 2 or 3 pm. There will even be widespread coverage from
Chatham to McIntosh and Long County late in the afternoon, where
the Atlantic sea breeze interacts with convection coming in
from the west-southwest.

Rainfall so far this month is around 1.5 to 2.5 inches above
climo, so it won`t take much to generate at least minor flooding
concerns, especially with the risk of back building and/or
training to occur. We anticipate at least minor flooding will
occur, and Flood Advisories could be required, mainly near the
I-95 corridor, as well as near the Beaufort area, where we have
a good 1.0 to 1.5 inches forecast. As usual locally higher
amounts will occur.

Conditions support a few strong to perhaps marginally severe
t-storms during the mid and late afternoon due to MLCAPE of
1500-2500 J/kg and some stronger mid and upper level winds
moving through. Where boundary interactions occur there could be
the consolidation of a few multicellular clusters capable of
generating localized downbursts. The better chances are over
inland South Carolina, but could be anywhere in Georgia.

Temperatures look to reach the upper 80s and lower 90s before
convection develops, but when it does, temperatures will drop
into the 70s.

Tonight: Convection shifts east through the evening, to the east
of I-905 early on, impacting the coastal corridor prior to
midnight, before activity pulls offshore and/or wanes due to the
loss of heating and the passage of a short wave. The higher QPF
amounts look to occur over Charleston County after dark, where
about 1/3 to 2/3 inches are forecast. Since it is convection,
locally higher amounts can occur. High tide over the coastal
counties this evening is generally around 8 or 9 pm, and there
could still be some moderate rains ongoing near those times. So
minor flooding could be a concern.

There could be some stratus and/or light fog forming if we get
enough clearing overnight. But not enough probability to show in
the forecast. Low temperatures will essentially be a persistence
forecast; lower and middle 70s.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY/...
Deep/closed upper level low pressure will continue to cycle through
eastern Canada through the short-term period with troughiness
extending all through way down through the eastern CONUS and
southwest flow through the southeast states. Stalled boundary will
also be lingering along the lee of the Appalachians with deep
moisture (PWAT values largely > 2 inches) draped through the Deep
South and southeast states. Daily heating/destabilization cycle
coupled with weak short-wave energy rippling through the region and
some larger scale forcing along the tail end of an upper jet will
lead to scattered-numerous showers and thunderstorms each day,
particularly during the afternoon and evening hours when instability
is greatest and the sea breeze is active. However, modest
instability could persist through overnight hours, so isolated
convection will be possible just about any time of day. Highs will
be in the lower to mid 90s each day with dewpoints in the 70s. Heat
indices currently expected to remain below Heat Advisory criteria.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
The typical summertime pattern will persist through next week with
deep layered ridging to our east across the Atlantic and tropical
moisture continuing to stream across the area. Scattered to numerous
mainly afternoon/evening showers and thunderstorms anticipated each
day. Daytime highs will continue to run in the lower to middle 90s
through the period with nighttime lows in the 70s.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
KCHS/KJZI/KSAV: Given the wet grounds and light or calm winds
there will be some low stratus around through mid morning,
mainly at KCHS and KJZI, where we have MVFR ceilings.

Convection will develop during the afternoon and continue into
this evening, resulting from daytime heating, the interaction of
various boundaries, and an added boost from a short wave moving
in late. For the 12Z TAFs we have higher confidence of flight
restrictions at KSAV, but all sites could experience sub-VFR
weather, especially between 19Z Saturday and 04Z Sunday.

The risk for low stratus and/or light fog late tonight is not
sufficient enough to show anything in the TAFs at this time.

Extended Aviation Outlook: Convection could produce brief flight
restrictions, especially each afternoon/evening.

&&

.MARINE...
The locally derived waterspout Index has an enhanced risk this
morning, the SPC Non-supercell Parameter shows 2-3 units over
the nearby waters, and satellite has a thin line of towering
cumulus, we opted to issue a Marine Weather Statement for the
possibility of waterspouts through this morning.

Today and tonight: The coastal waters will be positioned under
the west and northwest side of the typical sub-tropical ridge,
while a trough remains inland. There will be some modest
increases in the S and SW winds this afternoon with the sea
breeze, and maybe again tonight with nocturnal low level jet
enhancement. But in general, no more than about 15 or maybe 20
kt. Seas will average 2-4 feet, highest further out. Mariners
will experience t-storms throughout the period, most numerous in
coverage late this afternoon and early tonight. Marine Weather
Statements and/or Special Marine Warnings could be required for
winds in excess of 30 or 35 kt.

Saturday through Wednesday: Bermuda high pressure will remain the
dominant feature through the period. This will yield the typical
summertime southerly/southwesterly winds across the coastal waters.
The strongest winds will be along the coast each afternoon as the
sea breeze develops. We could also see a slight wind enhancement
along the coast overnight due to a nocturnal jet. Seas will average
2-4 ft.

Rip Currents: Based on the in-house calculator and the Rip
Current MOS Average both showing a low risk for today, that`s
what we`re forecasting. However, a low-end moderate risk
forecast for Sunday due to the 2-3 ft swell period increasing
from 7 to 8 seconds, combined with greater than normal tidal
range and daytime onshore winds.

&&

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

&&

$$

NEAR TERM...
SHORT TERM...Adam
LONG TERM...Adam
AVIATION...
MARINE...