Charleston, South Carolina Weather Forecast Discussion

788
FXUS62 KCHS 280618
AFDCHS
Area Forecast Discussion
National Weather Service Charleston SC
218 AM EDT Sun Sep 28 2025
.SYNOPSIS...
A weak front will remain stalled along the coast through today.
Tropical Depression Nine is forecast to become a tropical storm
near the Bahamas today then approach the Southeast U.S. coast
early next week as a tropical storm or hurricane.
&&
.NEAR TERM /THROUGH TONIGHT/...
Patchy to areas of fog and stratus across portions of SE GA/SC early
this morning should dissipate during the first hour or two of
daylight.
A broad H5 trough will remain across the forecast area through today
and tonight. At the sfc, a coastal trough will gradually deepen this
afternoon and evening, drifting inland. Instability will slowly
increase along the SC coast, peaking around 1000 J/kg. As the trough
shift onshore late this afternoon, scattered showers and
thunderstorms will develop along the coastal counties, especially
along the SC coast. High temperatures are forecast to range from the
low to mid 80s across the SC Lowcountry to the upper 80s across SE
GA.
Tonight, the sfc trough will continue to push inland through the
night. Moisture convergence and weak instability within the trough
should support scattered to numerous showers overnight. Low
temperatures are forecast to range around 70 degrees.
&&
.SHORT TERM /MONDAY THROUGH WEDNESDAY/...
A great amount of uncertainty still remains as Tropical Depression
Nine (TD9) approaches the region from central and northwestern
Bahamas. It is notable to point out that there has been this steady
trend in a slower northward track with TD9 in the deterministic
models and ensembles in last 24 hours, and this could have
significant impacts on the ultimate track. It seems like Hurricane
Humberto`s quick intensification and a more northeastward track is
having a greater influence on TD9 than previously expected. This
slower track means less interaction with the upper-lvl trough
situated across the Southeast and has the system taking a sharp
eastward turn with Humberto out to sea. This appears to be the most
likely scenario at the moment and the latest NHC track forecast has
shifted slower and further east in response. However, it is
important to note that there are still a couple outlier
solutions that stalls the system offshore and then has it make
landfall along the SC/NC coastline in the middle of next week as
a strong tropical system, or a weak hurricane. Right now, TD9
remains a broad, diffuse structure and is not showing signs of
intensification yet. However, steady intensification should
occur once the central core of the system develops.
Potential Impacts: If this slower northward track solution plays
out, the wind field is expected to expand quite a bit, and will pose
a risk of significant heavy rainfall, storm surge, and wind impacts
for the region even though the center of TD9 remains offshore in
this scenario. Everyone should prepare observe a high end tropical
storm, or low end hurricane wind speeds. Recent WPC guidance shows
the greatest precipitation along and east of I-95, with potential
for 4 to 6 inches possible. All residents should monitor the latest
forecast updates and ensure that they have their hurricane plan in
place.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
This forecast remains largely uncertain as most of it depends on the
movement and intensity of TD9. However, if TD9, follows this slower
track, then heavy rainfall could continue to be concern into
Wednesday night. Once TD9 heads out of the way, a strong upper-lvl
ridge will build down from southern Canada on Thursday through the
end of the week and allow for fairly breezy northeasterly winds to
take shape across the region. This will make it feel more like fall
next week as dry air advects down and dewpoints drop into the low to
mid 60s.
&&
.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
6Z TAFs: GOES Nighttime microphysics indicated an expanding area
of fog and stratus across inland SE GA/SC. Based on satellite
trends, fog and restrictive ceilings may spread over the
terminals during the pre-dawn hours. Each TAF will feature a
TEMPO from 9-12Z for MVFR vis and IFR ceiling. Conditions should
improve to VFR by 13Z. Showers and thunderstorms are forecast to
develop over the Hwy 17 corridor of Charleston County late this
afternoon. KCHS and KJZI TAFs will highlight the potential for
deep convection with PROB30 from 21-1Z. Forecast soundings and
MOS indicate that MVFR ceilings may develop across the terminals
this evening, beginning around 3Z.
Extended Aviation Forecast: A prolonged period of gusty north-
northeasterly winds possible Monday through Thursday due to
interactions between TD9 and inland high pressure. Expect MVFR, or
possibly lower ceilings and occasionally vsby reductions for
CHS/JZI/SAV beginning as early as Sunday night and persisting for
much of the week.
&&
.MARINE...
Today and tonight: The pattern will generally support an northeast
wind between 10 to 15 kts with gusts into the low 20s. Wave heights
should range between 3 to 4 ft today, increasing to 4 to 5 ft
tonight. Some 6 ft seas may reach the outer GA waters by daybreak
Monday.
Monday through Friday: As TD9 approaches the region from the from
central and northwestern Bahamas, expect northeasterly winds to
increase to 20 to 25 kts with gusts up to 30-35 kts by Monday
afternoon. Northeasterly winds will hold at this strength through
the end of the week as this upper-lvl ridge builds down from the
north and keeps the pressure gradient tight. Swell from TD9 with
some long period swell from Humberto will build into the local
waters on Monday causing seas to increase to 6 to 8 ft in the
nearshore waters, and 8 to 10 ft in the outer Georgia waters.
Heading into Tuesday and Wednesday, seas will continue increase and
seas will be 8 to 10 ft in the nearshore waters, and 10 to 14
(possibly 15 ft) in the outer Georgia waters. By Friday, the swell
should begin to taper off some, but seas will remain quite volatile
with waves reaching above 8 ft across all marine zones. Mariners
should closely monitor the tropics and the local marine forecast as
dangerous conditions are anticipated next week. In addition to the
strong winds and volatile seas, expect multiple rounds of showers
and thunderstorms as potential bands from TD9 traverse across the
local waters.
Rip Currents: Due to increasing swells and winds, a Moderate Risk of
rip currents is expected today for the SE GA beaches and a High Risk
for rip currents for all beaches on Monday. An enhanced risk will
continue through at least Wednesday.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.
&&
$$
NEAR TERM...NED
SHORT TERM...Dennis
LONG TERM...Dennis
AVIATION...Dennis/NED
MARINE...Dennis/NED

NWS CHS Office Area Forecast Discussion