Charleston, South Carolina Weather Forecast Discussion

372
FXUS62 KCHS 190917
AFDCHS
Area Forecast Discussion
National Weather Service Charleston SC
517 AM EDT Fri Sep 19 2025
.SYNOPSIS...
Weak high pressure will extend across the region this week.
Stronger high pressure will build into the region from the
north over the weekend and into early next week, while a
coastal trough develops offshore.
&&
.NEAR TERM /THROUGH TONIGHT/...
Satellite and surface observations show patches of shallow
ground fog are developing as expected, but its extent and
coverage is nowhere near what much of near term guidance members
were forecasting. KCLX also shows few showers have developed
across far interior Southeast Georgia. This activity should be
short-lived as daybreak approaches.
Through Tonight: Models show the broad, cyclonic flow that has
been place across the Southeast U.S. for the past several days
will persist through tonight, although it is becoming less
defined with time. Similar to Wednesday and Thursday, weak
impulses rounding the base of the trough will cross central
Georgia into Southeast Georgia and the South Carolina Lowcountry
this afternoon. Forcing with these impulses coupled convergence
ahead of the sea breeze may be enough to spark off another round
of isolated to perhaps scattered showers and tstms. Coverage may
not be as great as what was experienced Thursday afternoon owing
to slightly less mid-level RH, but the risk for measurable
rainfall is such that 20% pops were introduced for much of the
area along and west of the afternoon sea breeze. Convection
should quickly wane as sunset approaches with rain- free
conditions prevailing through the night. Another round of
shallow ground fog could occur as winds diminish and dewpoint
depressions approach zero.
Highs today will peak into the upper 80s/lower 90s with lower
80s at the beaches. Overnight lows will range from the mid-upper
60s inland to the lower-mid 70s at the beaches.
&&
.SHORT TERM /SATURDAY THROUGH MONDAY/...
A deep layer ridge will start the period, centered over the mid
Atlantic and northeast states. At the surface, a wedge of high
pressure will build southward from the mid Atlantic states
Saturday, while a weak trough of lower pressure forms over the
Atlantic waters. The ridge will shift eastward later Sunday and
Monday as a broad upper trough moves into the OH and TN River
valleys. This pattern will setup low level northeasterly winds,
which could get a bit breezy near the coast, with gusts of 15-20
mph possible, especially Sunday when the pressure gradient
looks to be the strongest.
No significant chances for rainfall through Sunday, with PoPs
below 15% as a deep layer of dry air remains over the region. By
Monday, blended model solutions start to bring in higher values
of deep layer moisture. Thus, have gone with slight chance to
low end chance PoPs, mainly for the eastern half of the forecast
area.
Temperatures, especially the high temperatures, are expected to
be near to slightly above normal on Saturday, then near to
slightly below normal Sunday and Monday. Humidity levels will
highest near the coast, with surface dewpoints near 70 through
the period. Lows generally mid to upper 60s, coolest inland, and
lower 70s closer to the coast.
&&
.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
The wedge of inland high pressure at the surface is shown by
global models to weaken and move eastward off of the mid
Atlantic coast Monday night into Tuesday. At upper levels, a
broad upper trough is shown by most models to move well north of
the area on Tuesday, then the flow generally becomes zonal
Wednesday through Friday. A weak surface front may stall over
the forecast area later Wednesday through Friday. With the
potential for increasing deep layer moisture and the presence of
a stalled surface front, have kept chance PoPs, mainly for the
afternoon hours. It should be noted that models diverge by mid
week on the upper flow pattern, which will lead to a good amount
of uncertainty in the overall forecast mid to late week.
Temperatures generally around normal through much of the period,
possibly falling below normal by Friday.
&&
.AVIATION /09Z FRIDAY THROUGH TUESDAY/...
19/12z TAFs:
KCHS/KJZI/KSAV: Some shallow ground fog will linger near the
terminals through daybreak. VFR will prevail through 20/12z.
Isolated showers/tstms will be possible this afternoon. The
impact risk looks too low to justify a mention at KJZI and KSAV,
but there has been a consistent enough signal in the guidance at
KCHS to include VCSH for the afternoon hours. Some shallow
ground fog could develop once again at the terminals prior to
daybreak Saturday. No major impacts are expected.
Extended Aviation Forecast: Through Sunday, VFR conditions are
expected to prevail at KCHS, KJZI and KSAV. By Monday and
Tuesday, expect a slight chance for showers, possibly a
thunderstorm with the potential for brief flight restrictions at
all sites.
&&
.MARINE...
Through Tonight: Southeast winds early this morning will back to
the north as daybreak approaches. These will then veer more
easterly near the coast this afternoon as the sea breeze
develops. Local sea breeze enhancements appear likely along the
land-sea interface with winds reaching as high as 10-15 kt with
gusts as high as 20 kt near the beaches and Charleston Harbor.
Otherwise, speeds will only average around 10 kt this afternoon.
Overnight, winds will tip back to the northeast as inland areas
cool. Seas will average 1-3 ft.
Saturday through Tuesday: Expect an increasing northeast
gradient Saturday and Sunday as a wedge of high pressure builds
inland and a trough of lower pressure forms over the eastern
Atlantic waters. Conditions are expected to remain just below
SCA levels, with winds generally 15-20 knots, with some gusts
near 25 knots possible. Seas generally 3 to 5 feet.
By Monday and Tuesday, the wedge of high pressure weakens and
moves eastward, allowing for lighter northeast winds, possibly
veering to southerly at 15 knots or less. Seas 2 to 4 feet.
Rip Currents: Increasing risk for rip currents still expected
into this weekend as gusty northeast winds develop between
strong high pressure inland, and coastal troughing offshore.
Increasing swell from the southeast will also favor a Moderate
Risk of rip currents along Georgia beaches by Saturday.
Conditions may support an enhanced risk of rip currents along
all beaches on Sunday.
&&
.TIDES/COASTAL FLOODING...
Strong northeasterly winds are expected to create larger tidal
departures this weekend, which could result in tide levels
approaching 7 ft MLLW (minor) in Charleston Harbor starting
with the Saturday evening high tide cycle. The risk for minor
coastal flooding should continue into early next week. Coastal
Flood Advisories could eventually be needed for minor saltwater
flooding in Charleston and Coastal Colleton Counties.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.
&&
$$

NWS CHS Office Area Forecast Discussion