Jamestown, South Carolina Weather Forecast Discussion

457
FXUS62 KCHS 140827
AFDCHS
Area Forecast Discussion
National Weather Service Charleston SC
427 AM EDT Sun Sep 14 2025
.SYNOPSIS...
High pressure will extend across the region this week. Low
pressure will develop well offshore into Monday before
meandering closer the North Carolina Outer Banks by mid week.
&&
.NEAR TERM /THROUGH TONIGHT/...
Today: On water vapor a baroclinic leaf has formed near coastal
South Carolina with dry air wrapping in on the back side of the low.
Latest 500 mb hand analysis revealed a mid-level ridge axis extending
well north with the 588 dam line extending to KMSP. Also noted
at 500 mb, was the well forecast shortwave beginning to wave
break over eastern Canada as it approaches the Maritimes. As
this occurs, surface cyclogenesis will continue east off of the
coast of South Carolina with pieces of vorticity beginning to
be absorbed by the primary shortwave over Canada. The wave
breaking will occur to far north though to completely absorb the
left over 500 mb low. However, this will keep the surface low
rather weak off of the South Carolina coast this afternoon.
Precipitation in association with the coastal low will be north
of the region with only high and mid clouds across the region
(albeit thick at times).
On the back side of the mid-level low PWATs will fall off to near
0.80" (or approaching daily minimum values for this time of year)
which will foster dewpoints mixing out into the lower to mid
50s with minimum RH values in the 25% to 35% range. Expect high
temperatures in the lower 80s across SC (with the thicker high
clouds) and mid to upper 80s for interior GA (due to mostly
clear skies and a dry air mass). No precipitation is expected
today.
Tonight: The mid-level low pressure will remain centered near the
South Carolina coast as the potent shortwave over the Canadian
Maritimes rapidly pulls east. The low dewpoints and climatologically
dry air mass will favor temperatures falling quickly as the sun sets
with lows Monday morning being in the upper 50s in rural locations
(were the winds completely decouple).
&&
.SHORT TERM /MONDAY THROUGH WEDNESDAY/...
The long span of quiet weather across the Lowcountry and Southeast
Georgia will persist. The sharp upper trough aligned along the
Southeast U.S. coast is steadily starting to pinch off from the
westerlies with a high amplitude ridge beginning to evolve into an
upper-level anticyclone over the Great Lakes. These two features
will eventually morph into a brief rex block with the upper low
meandering over the Carolinas and the upper high remaining quasi-
stationary over the Great Lakes. At the surface, guidance is
starting to converge on a more consolidated solution showing surface
cyclogenesis occurring well offshore of the South Carolina coast
which is supported by both the operational runs of the GFS and ECWMF
with strong support by most of their associated ensemble members.
Given the broad baroclinic leaf structure noted offshore of the
Southeast U.S. coast on both GOES-E IR and mid-level water vapor
imagery this morning, the strong signal of surface cyclogenesis
seems well supported.
The surface low is forecast to meander towards the North Carolina
Outer Banks and Crystal Coast regions through mid-week with any
direct shower activity associated with the low itself likely to
remain well offshore. A few showers could occur Monday afternoon and
evening east of the I-95 corridor in the Lowcountry where a weak sea
breeze could spark off some activity within a pocket of some
slightly higher moisture. Overall, mostly dry conditions will
prevail through mid-week as the inland wedge holds as the confluent
flow to the north helps to keep the parent high locked in over the
Mid-Atlantic states and will work in tandem with the increasing low-
level cyclonic flow induced by the developing surface low offshore
to help reinforce the wedge. Highs each day will peak mid-upper 80s
west of I-95 with lower-mid 80s at the coast and upper 70s/near 80
at the beaches. Readings could make a run for the 90 degree mark
across far interior Southeast Georgia by Wednesday. Lows each
morning will range from the lower-mid 60s inland, mid-upper 60s
coast with upper 60s/lower 70s at the beaches. A few upper 50s could
occur each night across the far interior, mainly in the typical
colder, more sheltered areas.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
The rex block over the eastern CONUS will quickly break down by mid-
week with broad ridging forecast to prevail across the Southeast
U.S. into Friday. A southern stream shortwave could impact the
region Saturday which could result in an uptick in rain chances as
the weekend begins. Highs will generally max out in mid 80s to lower
90s each afternoon (a bit cooler at the beaches) with overnight lows
dropping into the mid-upper 60s inland to the lower-mid 70s at the
beaches.
&&
.AVIATION /08Z SUNDAY THROUGH THURSDAY/...
Sunday 06z TAFs: VFR through the issuance expected. Surface low
pressure is beginning to from east of the South Carolina coast this
morning (as noted on water vapor) with high and mid clouds streaming
across KJZI and KCHS. No precipitation is expected today though as
the surface low meanders northeast.
Extended Aviation Forecast: There are no high confidence
concerns.
&&
.MARINE...
Today and Tonight: A surface low has already begun to form east of
the South Carolina coast this morning with precipitation remaining
past 20 nm. The surface low will keep the pressure gradient tight
though with wind gusts up to 25 kt and seas 3 to 6 ft. This
afternoon, the surface low will pull far enough north to allow
seas to fall below 6 ft across the nearshore GA waters. As such,
the Small Craft Advisory end time for the nearshore GA waters
has been moved up to 5 PM this afternoon. The nearshore SC and
offshore GA waters will maintain seas up to 6 ft and wind gusts
up to 25 kt through tonight though and therefore the Small
Craft will continue for the aforementioned zones.
Monday through Friday: The pinched gradient associated with the
inland wedge will begin to steadily relax Monday as low pressure
develops offshore and the wedge begins to build south. The tightest
pressure gradient will shift north of the waters Tuesday into
Wednesday as low pressure meanders north closer to the North
Carolina Outer Banks. This will result in a gradual decrease in both
winds and seas. The combination of lingering elevated winds and seas
will keep Small Craft Advisory conditions in place across the South
Santee-Edisto nearshore and the Georgia offshore legs into Monday
night. From Tuesday on, both winds and seas will remain below
advisory thresholds.
Rip Currents: Gusty northeast winds will persist today due to
the enhanced pressure gradient. This coupled with 4-5 ft swells
(and associated 8 second period) will keep a continued high
risk for rip currents along the Georgia beaches and a moderate
risk for the South Carolina beaches.
For Monday, lingering winds and elevated swell will keep the rip
current risk in the moderate category for all beaches.
&&
.TIDES/COASTAL FLOODING...
Today: A coastal flood advisory has been issued for Charleston
and Coastal Colleton counties this morning due to minor coastal
flooding forecast at Charleston Harbor. The tidal anomalies have
come down slightly from Saturday, but remain around +1 to +1.2
ft. This would favor a high tide around 7.3 ft MLLW at 224 PM
this afternoon. No coastal flooding is forecast at Fort Pulaski.
Monday through Wednesday: Tide levels will remain elevated
through the middle of next week due to large tidal departures
resulting from a pinched pressure gradient with persistent
northeast winds. The potential for coastal flooding will extend
into Monday with the early afternoon high tide cycle, especially
for coastal portions of Charleston and Colleton Counties.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...High Risk for Rip Currents through this evening for GAZ117-119-139-
     141.
SC...Coastal Flood Advisory from noon today to 4 PM EDT this
     afternoon for SCZ049-050.
MARINE...Small Craft Advisory until 2 AM EDT Tuesday for AMZ350-374.
     Small Craft Advisory until 8 PM EDT Monday for AMZ352.
     Small Craft Advisory until 5 PM EDT this afternoon for AMZ354.
&&
$$
NEAR TERM...Haines
SHORT TERM...
LONG TERM...
AVIATION...Haines
MARINE...Haines

NWS CHS Office Area Forecast Discussion