972
FXUS62 KCHS 041909
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
309 PM EDT Fri Jul 4 2025

.SYNOPSIS...
Low pressure is expected to develop off the Southeast coast
tonight, then move north toward eastern South Carolina Saturday
into Sunday. High pressure will rebuild next week.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
The latest SPC mesoanalysis indicated MLCAPE around 2000 J/kg with
normalized CAPE between .15-.2 units across the forecast area this
afternoon. Satellite Day Cloud Phase product indicated clusters of
developing cumulus and isolated showers inland of the sea breeze.
Based on the recent mesoanalysis and satellite trends, isolated to
scattered showers and thunderstorms should gradually develop through
the rest of the afternoon. Interestingly, at 18Z DCAPE values across
inland GA/SC ranged from 1000-1400 J/kg. The DCAPE values will
likely decrease as the sea breeze approaches, however, values may
remain around 1000 J/kg. It is possible that one or two storms may
develop strong wind gusts.

Deep convection across SE GA/SC should dissipate this evening. Low
pressure off the Southeast U.S. coast will slowly track towards the
Carolina coast tonight. As the system approaches, it could become
better organized and could strengthen over the Gulf Stream. See
latest NHC information. Rain bands should push onshore along the
coast of the South Carolina Lowcountry late tonight into early
Saturday morning. The forecast will feature a tight gradient of PoPs
from likely across the adjacent Atlantic waters to SCHC PoPs along
the I-95 corridor. In addition, northeast winds along the coast will
gradually strengthen, with gusts around 25 mph possible along the
beaches late tonight. Low temperatures are forecast to range from
near 70 inland to the mid to upper 70s along the coast.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
The main concern over the weekend is a low pressure system well
off the GA/SC coast that is forecast by most models to gradually
strengthen as it moves NNW or N. An NHC aircraft is
investigating the system this afternoon so more information
should be available later this afternoon or early this evening.
The 12Z guidance is in reasonably good agreement that the system
would slowly strengthen as it moves NNW, then moves inland over
eastern SC somewhere between Charleston and the SC/NC border on
Sunday. There are currently no indications that it would
strengthen substantially. The reasonable worst case scenario
would be for it to strengthen into a low-end tropical or
subtropical storm before it makes landfall in SC during the day
Sunday. The latest NBM probabilistic guidance shows only a 10%
chance for peak wind gusts along the SC coast to exceed 45 mph
during the strongest winds Saturday afternoon/night.

A very moist airmass will overspread the area Saturday. PWATs
will exceed 2.2" over the eastern half of the area by Saturday
afternoon, then this moisture will spread across the remainder
of the area Saturday night into Sunday. An increase in cloud
cover will depress temperatures somewhat, which in turn will
limit instability. However, approximately 1000 J/kg CAPE
expected during the daytime hours both days. Isolated to
scattered showers and tstms could develop Saturday morning in
response to an early sea breeze, then greater coverage will
overspread the area from the east as rain bands from the low
move in.

Numerous showers and tstms will likely continue Saturday night
into Sunday morning until the low pressure system moves inland
over eastern SC and dissipates. Locally heavy rainfall will be
possible Saturday through Sunday given the very moist airmass
and potential for training cells.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
A deep layered ridge will build over the eastern U.S. next week,
with increasing temperatures and dewpoints. Heat indices
expected to rise above 108F for many areas Tuesday through
Thursday so Heat Advisories are possible.

&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
Prior to the 18Z TAFs, visible satellite indicated that the sea
breeze has pushed inland of the terminals. Convection this
afternoon should favor areas along and ahead of the sea breeze,
TAFs will indicate dry weather. East winds are forecast to
remain between 10 to 15 kts with gusts near 20 kts through the
rest of this afternoon. A coastal low will approach tonight into
Saturday. Rain bands and deep moisture associated with low are
timed to push onshore along the SC coast during the pre-dawn
hours, edging inland through the rest of the 18Z TAF period.
KCHS and KJZI will feature a mention of -SHRA by daybreak with a
TEMPO at KJZI from 12-16Z for -TSRA. As the system nears the
coast, it is expected to interact with an area of high pressure
centered over the Mid Atlantic states, resulting in gusty
northeast winds north of the center of low pressure. The
terminals may see gusts around 25 kts after sunrise Saturday.

Extended Aviation Outlook: Occasional ceiling restrictions
possible Saturday through Sunday as low pressure moves up the
coast. Brief ceiling/vsby restrictions possible Saturday through
Wednesday due to scattered showers and thunderstorms.

&&

.MARINE...
Tonight, low pressure off the Southeast U.S. coast will slowly track
towards the Carolina coast tonight. As the system approaches, it
could become better organized and could strengthen over the Gulf
Stream. See latest NHC information. As the system nears the coast,
it is expected to interact with an area of high pressure centered
over the Mid Atlantic states, resulting in gusty northeast winds
north of the center of low pressure. By late tonight, northeast
winds are forecast to strengthen to 20 kt with gusts around 25 kts.
In addition, seas should build through tonight, generally ranging
between 4 to 5 ft by sunrise Saturday.

The main challenge will be what happens to the developing low
pressure off the GA coast. It has the potential to develop into
a subtropical or tropical depression tonight, then possibly into
a low-end tropical/subtropical storm Saturday or Saturday night.
12Z guidance is in reasonably good agreement that this system
would move north toward the eastern SC coast, potentially moving
inland between Charleston and Myrtle Beach Sunday morning.

Regardless of the exact type and strength of the system, we
anticipate a tightening northeast gradient along the coast on
Saturday between the low pressure offshore and inland high
pressure. 6 ft seas and 25-30 kt wind gusts could spread into
the SC nearshore waters during the day Saturday, continuing into
Saturday night. These gusty winds would also impact Charleston
Harbor. We held off on the issuance of a Small Craft Advisory
with this package until we get more information later this
afternoon about the potential strength and track of the
offshore low pressure.

Conditions will drastically improve on Sunday as the flow
briefly becomes offshore, then settles into a SW flow as high
pressure rebuilds.

Rip Currents: Gusty winds and increasing swell energy will yield
a High Risk for rip currents along the SC coast and Moderate
risk for GA coast on Saturday. A Moderate Risk exists for all
beaches on Sunday, mainly due to residual swell.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...High Risk for Rip Currents from Saturday morning through Saturday
     evening for SCZ048>051.
MARINE...None.

&&

$$

NEAR TERM...NED
SHORT TERM...JRL
LONG TERM...JRL
AVIATION...JRL/NED
MARINE...JRL/NED