Saint Stephen South Carolina Weather Forecast Discussion

037
FXUS62 KCHS 071758
AFDCHS
Area Forecast Discussion
National Weather Service Charleston SC
158 PM EDT Tue Oct 7 2025
.SYNOPSIS...
High pressure will persist into Wednesday. A cold front will
drop south through the area Wednesday night into Thursday with
inland high pressure prevailing into early next week. Low
pressure will develop off the Southeast U.S. coast this
weekend.
&&
.NEAR TERM /THROUGH TONIGHT/...
Early afternoon surface observations show the coastal trough
stubbornly remaining along the coast, with radar showing weak
scattered showers moving across the area. Guidance now suggests that
the weak trough should remain along the coast, or at least near the
coast, with temperatures in the lower 80s. The weak scattered
showers should linger into the late afternoon hours before
dissipating given the weak lift. Heading into the evening hours, a
weak surface high pressure develops across central South Carolina
into far eastern Georgia on the northern edge of the ridge aloft,
which does look to finally mix out the coastal trough. Basically
under the center of the high pressure, the winds will be weak and
given the continued dreary and damp conditions there is potential
for fog overnight. The NBM would suggest only a 20% chance for
visibilities below 1 mile, while the convection-allowing ensembles
(REFS and HREF) are more convinced with probabilities up to 60%.
Given the rain showers lingering into the late afternoon hours,
which helps increase moisture content in the boundary layer, can`t
rule out at least isolated quarter-mile visibilities by Wednesday
morning. Overnight lows in the mid to upper 60s expected.
&&
.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
Wednesday: A potent shortwave exiting out of the Great Lakes and
across the Northeast U.S. will help drive a cold front south into
the Southeast U.S. Wednesday. The front looks to remain to the west
and northwest through during the day, then backdoors into area
overnight as high pressure begins to wedge south. Quasi-geostrophic
forcing associated a passing lobe of mostly channeled vorticity
aloft looks a bit stronger in the guidance than what depicted Monday
with modest deep-layered UVVs noted on model cross-sections,
especially as the front pushes into southern South Carolina. With
sufficient lift and moisture in place, it does appear a band of
scattered light to moderate showers with possibly a few tstms will
accompany the front with most of the activity occurring Wednesday
night. The frontal structure is looking a bit more anafrontal with
some isentropic ascent noted atop the deepening inland wedge in
addition to the QG-forcing previously noted. This will likely result
in most of the shower activity occurring behind front. Pops 30-50%
were maintained north of I-16 Wednesday night (highest far interior
into the Charleston Tri-County area) with 20-30% pops elsewhere.
Highs will warm into the upper 80s away from the immediate coast
with a few spots across mainly interior Southeast Georgia making a
run for the 90 degree mark. Overnight lows will drop into the 60s as
cooler, drier air begins to advect south behind the front.
Thursday and Friday: Some degree of post-frontal rains may be
ongoing Thursday morning, especially over Southeast Georgia. The
wedge will become further established during the day Thursday as the
1035 hPa parent high shifts into New England and the confluent flow
across the northeastern U.S. becomes better defined. The risk for
some showers moving onshore with the northeast low-level flow will
persist into Friday with most of the activity likely being
redirected into northeastern Florida. 07/13z NBM pops of 20-50% at
the coast are likely overdone, especially along the lower South
Carolina coast, but were maintained as "Break the Glass" criteria is
not met. It will be considerably cooler both days with highs ranging
from the upper 60s/lower 70s north of I-16 (coolest interior
Southeast South Carolina) with mid 70s elsewhere. Highs Friday could
be a few degrees warmer, but still well below normal with most areas
holding in the 70s. Lows Friday morning will drop into the mid-upper
50s inland to the lower-mid 60s closer to the coast. Breezy to
locally windy conditions will occur across the coastal corridor,
especially near the immediate coast and beaches both days where a
very tight pressure gradient will occur with the building wedge.
Lake Winds: Winds on Lake Moultrie are expected to increase Thursday
into Friday in response to a tightening pressure gradient associated
with and inland wedge. Winds could reach as high as 20 kt with gusts
to 25-30 kt both days with waves building as high as 2-3 ft. A Lake
Wind Advisory may be needed.
&&
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Confidence continues to grow that rapid cyclogenesis will occur off
the Southeast U.S. Coast Friday night into Saturday in response to a
developing upper low interacting with a coastal trough offshore and
solid Gulf Stream induced baroclinicity. While is still lingering
uncertainty on exactly where the surface low will form and
eventually track, there does appear to be a bit more consistency in
the GFS and ECMWF ensemble members compared to Monday. Most of the
rain impacts will remain offshore although some coastal showers
could still rotate onshore through Saturday before even drier air
advects south as it pulls away from the area. Slight chance pops
were maintained for the coastal corridor Friday night into Saturday
to account for this. Breezy to locally windy conditions will linger
near the coast and beaches. Rain-free conditions will dominate
Sunday into Tuesday as inland high pressure becomes reinforced by
the cyclonic flow around the departing surface low. Below normal
temperatures over the weekend will gradually moderate to more
seasonable levels Monday into Tuesday.
Lake Winds: Hazardous conditions will persist on Lake Moultrie
Friday night into Saturday with winds as high as 20 kt with gusts 25-
30 kt and waves 2-3 ft. Winds will begin to subside Sunday as the
pressure gradient relaxes in response to departing low pressure. A
Lake Wind Advisory may be needed.
&&
.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
Scattered light rain showers continue to move across the region,
mostly south of I-26. MVFR to IFR cigs and visbys are accompanying
the showers at times, resulting in quickly changing conditions as
showers move over any given location. Rain showers will be
dissipating throughout the afternoon hours, bringing the lowered
flight categories along with them. However, the break from flight
restrictions will be brief as chances for fog increase into the
overnight hours and early morning hours on Wednesday.
Extended Aviation Outlook: Gusty north to northeast winds will impact
the terminals Thursday and Friday, possibly lingering into Saturday
as a strong wedge develops inland and low pressure forms offshore.
There are no other high confidence concerns at this time.
&&
.MARINE...
Through Tonight: Light rain showers will be moving out of the waters
into the late afternoon hours, with winds well below small craft
advisory. Near-shore waters will continue to see 3 to 5 waves, while
outer Georgia waters are in the 5 to 6 foot range, with seas calming
down overnight which will allow for the small craft advisory in the
outer Georgia waters to expire. In the late overnight/early morning
hours, we could see some patchy fog along the coast, possibly
spilling over into the Charleston Harbor and/or the entrance to the
Savannah River.
Wednesday: High pressure over the Atlantic will give way to an
approaching cold front Wednesday night. Winds Wednesday will
generally be out of east and southeast 10 kt or less with some
degree of sea breeze enhancements in the Charleston Harbor and along
the land/sea interface during the afternoon hours. Winds will
quickly turn northeast late Wednesday night as a backdoor front
surges south and a wedge of high pressure strengthens inland. Winds
from the South Santee-Edisto Beach nearshore leg and possibly
Charleston Harbor have the greatest chance of reaching Small Craft
Advisory criteria (20 kt with gusts 25-30 kt, except 15-20 kt with
gusts to 25 kt in the Charleston Harbor) by daybreak Thursday. Waves
will average 3-4 ft nearshore waters and 4-5 ft offshore waters both
Wednesday and Wednesday night.
Thursday through Sunday: Confidence is high that a hazardous marine
event will impact the coastal waters beginning Thursday and lingering
into the weekend the region gets pinned between low pressure
developing offshore and wedge of high pressure inland. The risk for
gale conditions is increasing within the resulting pinched gradient
with the probabilities of seeing frequent gusts to 35-40 kt running
between 50-70% per the latest LREF Grand Ensemble. Northeast gales
could develop as early as Thursday with winds peaking (25-30 kt with
gusts 35-40 kt) roughly in the Thursday night to Saturday time frame
before slowly diminishing and backing more northerly Friday night
into Saturday as low pressure begins to develop offshore. Winds will
further diminish into Sunday. Gale Watches and Warnings are likely
with a Small Craft Advisory in the Charleston Harbor (although wind
gusts could get close to gales near the entrance). Seas will peak 6-
10 ft nearshore waters and 10-13 ft over the Georgia offshore waters
for the even with waves as high a 2-3 ft in the Charleston Harbor.
Rip Currents: A lingering 8-9 sec swell will keep the rip current
risk into the moderate range for all beaches Wednesday. The risk
tips into the high category once again for all beaches Thursday as
northeast winds increase behind a backdoor wedge front. An enhanced
risk will linger through early next week due to a combination of
gusty winds and building surf.
High Surf: The risk for high surf will increase Thursday night into
Saturday as wave heights build across the coastal waters due to a
combination of wind wave and 9-11 sec easterly swell. A High Surf
Advisory may be needed for some area beaches.
&&
.TIDES/COASTAL FLOODING...
Latest tide observations and guidance supports minor coastal
flooding for Charleston and Coastal Colleton Counties with this
evenings high tide, which will be occurring 8:01 PM this
evening. Coastal flooding is possible an hour prior starting at
7 PM as we approach 7 ft MLLW, with the crest this evening
expected to stay in the 7.1 to 7.3 ft MLLW range, dropping back
below flood stage by 10 PM.
Astronomical tides will continue to increase this week due to the
full moon today (Oct 7) and perigee (Oct 8). Additionally, tidal
departure values will begin to increase again late week and into the
weekend due to strong NE winds. As a result, the threat for minor to
moderate coastal flooding continues through mid-week. Late week the
threat for major coastal flooding arrives for the late morning high
tides.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...High Risk for Rip Currents until 8 PM EDT this evening for GAZ117-
     119-139-141.
SC...Coastal Flood Advisory from 7 PM to 10 PM EDT this evening for
     SCZ049-050.
MARINE...Small Craft Advisory until 6 AM EDT Wednesday for AMZ374.
&&
$$
NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...

NWS CHS Office Area Forecast Discussion