031
FXUS62 KCHS 050035
AFDCHS

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

.SYNOPSIS...
A tropical system is expected to move slowly north-northwest
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/...
As we head into the overnight, convection across SE GA/SC has
mostly cleared out for the evening. Earlier this afternoon, the
aforementioned low pressure off the Southeast U.S. coast formed
into a tropical depression. NHC has labeled the name of the
system as Tropical Depression Three. Charleston County is
currently under a Tropical Storm Watch until Sunday. As the
system approaches the coast, it could become better organized
and could strengthen over the Gulf Stream. Thus, this might
yield Tropical Storm Warnings if this does happen. Regardless
of the strength, 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 /00Z SATURDAY THROUGH WEDNESDAY/...
00Z TAFs: Showers and thunderstorms have cleared out for the
most part across the Lowcountry as we head into the overnight.
A tropical depression 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 00Z TAF period. KCHS and KJZI
will feature a TEMPO at all terminals for -SHRA by daybreak. 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. As rainbands from this system continue to
break off throughout the day and move onshore, a TEMPO groups
was added at all terminals for -TSRA beginning at 18Z. Outside
of the TEMPO group, all terminals will feature a mention of VCSH
throughout the day.

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: A tropical depression 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.

This tropical depression has the potential to develop into
tropical storm Saturday or Saturday night. Recent guidance
suggests this system would move north toward the eastern SC
coast, potentially moving onshore 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.

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...Tropical Storm Watch for SCZ050.
     High Risk for Rip Currents from Saturday morning through Saturday
     evening for SCZ048>051.
MARINE...Tropical Storm Watch for AMZ330-350.
     Small Craft Advisory until noon EDT Sunday for AMZ352.
     Small Craft Advisory until 6 AM EDT Sunday for AMZ354-374.

&&

$$

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