Saint Helena Island, South Carolina Weather Forecast Discussion

441
FXUS62 KCHS 300621
AFDCHS
Area Forecast Discussion
National Weather Service Charleston SC
221 AM EDT Tue Sep 30 2025
.SYNOPSIS...
Tropical Storm Imelda will move northeast away from the
Southeast U.S. coast tonight through Wednesday. A cool, dry
high pressure will then build in from Canada and allow for
fall-like weather to take place towards the end of the week.
&&
.NEAR TERM /THROUGH TODAY/...
The forecast area will remain between a sfc ridge across the western
Carolinas and Imelda and Humberto over the western Atlantic. The
pressure gradient across the forecast area will support gusty north-
northeast winds through most of the near term period. Temperatures
today will be limited by the gusty NNE winds and thick cloud cover,
highs ranging from the upper 70s across the SC Lowcountry to the low
80s across SE GA. Light rain may occur from time to time within a
plume of deep moisture across the Atlantic waters and coastal
counties. QPF should remain less than a tenth of an inch.
Tonight, drier air will dive southward across the forecast area as
the tropical cyclones track to the east. The arrival of the drier
air should end and SCHC PoPs with decreasing cloud cover. Low
temperatures are forecast to range from the low 60s inland to the
mid 60s along the coast.
&&
.SHORT TERM /TONIGHT THROUGH FRIDAY/...
As Imelda pushes farther away from the CONUS, strong Canadian high
pressure will build in from the northwest and advect drier air into
the region. This allow for a decrease in cloud coverage and breezy
north-northeasterly winds to persist across the region (w/ winds
highest near the coastline)as the local pressure gradient over the
region tightens up. With the dry and cool airmass present, PWATs
will fall well below normal on Thursday and Friday and this will
support a more fall-like climate with temperatures in the mid to
upper 70s. Additionally, dewpoints will drop into the upper 50s and
low 60s! Thereafter, ensembles have been depicting an weak coastal
trough forming in the Gulf and into the Deep South on Friday, and
then becoming entrapped under this building high pressure from the
northwest. This will trough will slowly allow for moisture to return
to the region on Friday and expect chance for shower and
thunderstorm activity to increase Friday afternoon (mainly along
the immediate coastline).
&&
.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
There is some uncertainty this weekend depending on how quickly the
moisture returns and how this weak coastal trough situated over the
Deep South evolves throughout the period. Some model guidance has
been hinting at the trough shifting more inland towards the region
over the weekend, with some ensembles showing it dissipating before
even reaching our area. Regardless, given the moisture returning,
it`s possible to see isolated to scattered showers and thunderstorms
develop along and east of I-95 each afternoon/evening through early
next week. Temperatures should gradually warm back up to near normal
on Sunday and Monday as upper-lvl heights increase and flow turns to
the more to the east.
&&
.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
6Z TAFs: Regional observations indicated widespread IFR to MVFR
ceilings across the Southeast U.S. Based on simulated satellite
products, restrictive ceilings should remain across the
terminals until around sunset today. Each TAF will indicate IFR
to MVFR ceilings until 1Z Wed. Otherwise, terminals will remain
within a tight pressure gradient between Imelda and a ridge of
high pressure over the western Carolinas. North-northeast winds
should remain between 10 to 15 kts with gusts between 20-25 kts.
Extended Aviation Forecast: An extended period of sub-VFR ceilings
could possibly continue through Tuesday night, along with occasional
vsby reductions due to showers and thunderstorms. Also, expect
breezy northeasterly winds through Wednesday.
&&
.MARINE...
Today and tonight: The marine zones will remain between a ridge
across the western Carolinas and Imelda and Humberto over the
western Atlantic. Northeast winds will remain between 20 to 25 kts
with gusts into the low 30s through this evening. Winds may begin to
slowly weaken late tonight. Swell sourced from major hurricane
Humberto and strengthening Imelda will build across the marine zones
through today. By late this afternoon, seas should peak from 8 to 14
ft. Small Craft Advisories are in effect for all marine zones
through the near term.
Wednesday through Sunday: Breezy north-northeasterly winds at 20 to
25 kt with gusts up to 30-33 kt will likely hold through the latter
part of the week as Imelda and Hurricane Humberto meander over the
western Atlantic and a strong high pressure builds down from Canada
allowing for the pressure gradient to tighten up across the local
waters. Additionally, swell from Imelda with long-period swell from
Humberto will continue to build into the local waters through the
weekend causing seas to slowly increase to 8 to 10 ft in the
nearshore waters, and 10 to 12 ft in the outer Georgia waters
(possibly 14-15 ft) on Wednesday and Thursday. By Friday, the swell
should begin to taper off some, but seas will remain quite volatile
into the weekend with waves +6 ft across all marine zones.
Therefore, Small Craft Advisories (SCAs) have been issued for all
marine zones through the end of the week w/ the Charleston Harbor
SCA likely ending sooner) due the combination of high winds and
seas.
Rip Currents/High Surf: A High Risk of rip currents is expected
Tuesday (today) and Wednesday at all beaches due to large,
long- period swells and strong winds. In addition, large
breaking waves of 5+ feet are expected through much of the week
and a High Surf Advisory remains in effect.
&&
.TIDES/COASTAL FLOODING...
Strengthening and persistent north-northeasterly winds and swell
wave run-up this week will result in increasing tidal
departures along the southeast South Carolina and southeast
Georgia coast. Minor coastal flooding is possible during the
late afternoon/early evening high tide cycle, mainly for the
Charleston and Colleton County coastlines, starting as early as
this afternoon. The risk will continue into late week.
Heading into this weekend and early next week, astronomical tides
will increase due to the upcoming Full Moon (Oct 7) and Perigee (Oct
8). This in combination with the anticipation of continued
northeasterly flow will cause the possibility of coastal flooding to
become more likely along the entire coastline, including both
Downtown Charleston and Fort Pulaski. Saltwater inundation could
then occur during both the morning and evening high tide cycles
during this time. Although there is considerable uncertainty this
far out, persistent favorable winds have the potential to produce up
to major coastal flooding.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...High Risk for Rip Currents through this evening for GAZ117-119-139-
     141.
     High Surf Advisory until 8 AM EDT Saturday for GAZ117-119-139-
     141.
SC...High Risk for Rip Currents through this evening for SCZ048>051.
     High Surf Advisory until 8 AM EDT Saturday for SCZ048>051.
MARINE...Small Craft Advisory until 2 AM EDT Wednesday for AMZ330.
     Small Craft Advisory until 2 AM EDT Monday for AMZ350-352-354.
     Small Craft Advisory until 8 PM EDT Monday for AMZ374.
&&
$$
NEAR TERM...NED
SHORT TERM...Dennis
LONG TERM...Dennis
AVIATION...Dennis/NED
MARINE...Dennis/NED

NWS CHS Office Area Forecast Discussion