Cainhoy, South Carolina Weather Forecast Discussion

756
FXUS62 KCHS 290055
AFDCHS
Area Forecast Discussion
National Weather Service Charleston SC
855 PM EDT Sun Sep 28 2025
.SYNOPSIS...
Tropical Storm Imelda will move through the northern Bahamas
Monday, then northeast away from the Southeast coast Tuesday
and Wednesday. Cooler high pressure will then build in from the
northwest.
&&
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
Tonight: The mid-levels consist of a broad trough over the Southeast
U.S. At the surface, a stationary front is located just off our
coast. While the front could drift back toward the coast this
evening, it is expected to move back offshore overnight. The setup
continues to usher deep moisture into our region, with PWATs near
1.7 to 2 inches closer to the coast. The CAMs and the deterministic
models have showers approaching the coast this evening, then moving
onshore by late evening, before potentially shifting further inland
(I-95 corridor) late. Locally heavy rainfall is possible, mainly
near the coast, which is where WPC continues to highlight the local
area under a Marginal Risk for excessive rainfall. Even with this in
mind, rainfall accumulations should generally remain around an inch
or less with the risk for widespread flash flooding being low. Low
temperatures will be around 70 degrees.
&&
.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
Tropical Storm Imelda is forecast to move slowly north and out
of the Bahamas on Monday while gradually strengthening.
Fortunately the guidance and official forecast continue to show
the system turning abruptly to the ENE on Tuesday, keeping the
system well away from SC/GA. However, we still expect some
impacts, primarily from rainfall, marine winds, coastal
flooding, and high surf and rip currents.
A fairly large area of 2+ PWATs is forecast to overspread
southern SC and coastal GA Monday and remain in place through
Tuesday before drier high pressure sinks into the area from the
northwest Tuesday night and Wednesday. Most guidance continues
to show a large area of synoptic forcing across the eastern half
of the area between an in-situ upper trough and Imelda
offshore, particularly Monday into Tuesday. There should be
ample moisture and forcing for ascent for scattered to numerous
showers and a few tstms. Models have been trending downward with
overall QPF, though we still show the potential for 1-3" across
the eastern half of the Charleston Tri-County Area Monday-
Tuesday.
Tuesday night and Wednesday now look dry as strong high
pressure builds in from the north and west as Imelda pushes
farther away from the Southeast coast.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Cool and dry weather expected for most of the area Wednesday
night through Friday, though a weak coastal trough along the GA
coast could bring isolated showers to far southern areas. The
weekend is trending wetter with the potential for Gulf low
pressure to move north toward the area.
&&
.AVIATION /00Z MONDAY THROUGH FRIDAY/...
TEMPO MVFR cigs are possible at CHS/JZI/SAV terminals between 00-03Z
Monday as low stratus shifts onshore, before MVFR cigs prevail into
early morning hours at all sites. Light showers could produce lower
cig/vsby conditions prior to midnight, but the bulk of guidance
supports IFR conditions and light showers by around 07Z Monday at
all terminals, which should persist through at least 18Z Monday and
possibly through 00Z Tuesday with moderate showers also impacting
the terminals through a bulk of the afternoon. However, a few hour
period of MVFR cigs could return Monday afternoon while northwesterly
winds become gusty at all terminals, generally in the 15-20 kt range.
Confidence in improving conditions temporarily Monday afternoon
is too low to introduce prevailing groups at any terminal at this
time.
Extended Aviation Forecast: An extended period of MVFR ceilings
is expected through Tuesday night or Wednesday, along with
occasional vsby reductions due to showers and thunderstorms.
Gusty NE winds also expected through Wednesday.
&&
.MARINE...
Tonight: A stationary front will meander over or just east of local
waters overnight, resulting in a gusty showers and/or thunderstorms
drifting across coastal waters for much of the night. Outside this
activity, the pressure gradient will slowly tighten across local
waters between high pressure inland and tropical low pressure well
offshore. This will generally yield northeast winds in the 15-20 kt
range with a few higher gusts. Seas will also slowly build through
the period, from 2-4 ft to 4-5 ft overnight. However, latest marine
obs indicate 5 ft seas already at buoy 41008. Given the earlier
arrival of larger seas, have initiated the Small Craft Advisory
across outer Georgia waters at 2 AM tonight. Elsewhere, conditions
should remain just below Small Craft Advisory levels through
the night.
A prolonged period of strong NNE winds expected Monday through
Saturday due to a tight gradient between inland high pressure
and TS Imelda offshore. We have Small Craft Advisories for all
waters except Charleston Harbor starting Monday morning,
continuing through Friday night, for a combination of winds/seas.
We`ll likely eventually need a Small Craft Advisory for
Charleston Harbor starting later Monday or Monday night.
Rip Currents: A High Risk of Rip Currents will continue through
at least Tuesday due to large, long-period swells and strong
winds.
&&
.TIDES/COASTAL FLOODING...
Strengthening NNE winds this week will result in an increase in
tidal anomalies. There is quite a bit of uncertainty about
exactly how large the positive anomaly will be given that the
wind directions could be more NNE rather than NE. There is a
fine line between what wind directions cause the greatest Ekman
forcing along the SC/GA coast. A wind direction closer to 040
degrees is much more favorable than 010-020 degrees. The latest
forecast for Imelda points toward a more northerly fetch, in
which case the anomaly may not get much higher than +1.6 ft. We
trended the tide forecast upward a bit with the morning
forecast, but at this point the only flooding we are showing is
minor coastal flooding at Charleston Wednesday afternoon.
A High Surf Advisory may be needed for part or all of the
coastline as early as Monday afternoon, though the greatest
threat for 5+ ft breaking waves would be Tuesday and Tuesday
night.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...High Risk for Rip Currents from 8 AM EDT Monday through Monday
     evening for GAZ117-119-139-141.
SC...High Risk for Rip Currents from 8 AM EDT Monday through Monday
     evening for SCZ048>051.
MARINE...Small Craft Advisory from 10 AM Monday to 8 AM EDT Saturday
     for AMZ350-352-354.
     Small Craft Advisory from 2 AM Monday to 8 AM EDT Saturday for
     AMZ374.
&&
$$
NEAR TERM...DPB
SHORT TERM...JRL
LONG TERM...JRL
AVIATION...DPB/JRL
MARINE...DPB/JRL

NWS CHS Office Area Forecast Discussion