Charleston, South Carolina 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

634
FXUS62 KCHS 150556
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
156 AM EDT Fri Aug 15 2025

.SYNOPSIS...
A weak cold front will pass through the region on Saturday and
increase rain chances over the weekend. Thereafter, high
pressure will build into the region as Erin passes well offshore
to the east, likely as a hurricane.

&&

.NEAR TERM /THROUGH TONIGHT/...
The upper-level high over Florida will maintain its influence
today as the Atlantic surface high builds west. Heights at 500
hPa are forecast to nudge slightly higher through the afternoon
as the center of upper high meander a bit farther to the north.
A weak surface trough is progged to drop south into parts of the
Lowcountry this afternoon as a weak cyclogenesis tries to
initiate just off the North Carolina Crystal Coast in response
to passing shortwave energy off the Outer Banks. This feature
could interact with the afternoon sea breeze to help spark off
convection along the lower South Carolina coast with additional
isolated to scattered activity forming farther inland as
mixed-layer instability builds and mesoscale boundary collisions
begin. Modified soundings show moderate to strong instability
building through the day (MLCAPE 3500-4000 J/kg) as dewpoints
hold well into the 70s with PWATs in the 2.0-2.3" range. The
coverage of showers/tstms will remain somewhat curtailed given
the lack of shortwave forcing aloft and warm 500 hPa temperatures.
Pops 20-40% were highlighted for all areas this afternoon.
Shear is forecast to remain weak, but with somewhat elevated
DCAPE values of 800-1000 J/kg in place, a few strong could occur
with gusty winds and frequent cloud-to-ground lighting. An
isolated severe tstm with damaging winds could also occur,
especially where updrafts are enhanced near boundary interactions.
There is a risk for locally heavy rainfall with at least minor
flooding of low-lying and poor drainage areas possible. HREF
neighborhood probabilities are ~30-60% for >1" in 3 hrs (highest
over southern South Carolina) and 10% for >3" in 3 hrs centered
over the Charleston Tri-County. The risk for flash flooding
would increase over the Charleston Metro Area, particularly in
Downtown Charleston, if tstms were concentrate there as some
CAM members suggest. Convection will slowly wane this evening
with redevelopment possible over the Atlantic after midnight.

Hot and muggy conditions will persist. Highs are expected to
peak in the lower-mid 90s. Dewpoints should mix out in the
lower-mid 70s across the interior with upper 70s/near 80 holding
across the coastal corridor. This yields heat indices of 103-107
inland and across the Charleston Tri-County with 108-112 across
the Georgia coastal counties and up into Jasper and Beaufort
Counties in the Lowcountry. A Heat Advisory remains in effect
from 11 AM to 6 PM for these areas. If convection is slower to
spark along the Charleston and Colleton County coasts, then a
northward extension of the advisory may need to be considered.
For now, it is assumed convection will initiate early enough to
keep heat indices below the 108 threshold. Warm and humid
conditions will linger into tonight with lows dropping in the
lower-mid 70s inland with upper 70s/near 80 closer to the coast
and beaches, including Downtown Charleston.

&&

.SHORT TERM /SATURDAY THROUGH MONDAY/...
As an upper-lvl ridge builds over central CONUS, a weak area of
low pressure will shift northeastward offshore. Simultaneously,
a weak cold front associated with the weak low will drop in
from the north on Saturday, then move offshore by Sunday
morning. With an ample amount of moisture (PWATs > 2.0")
remaining over the Southeast, expect scattered showers and
thunderstorms to develop in the afternoon and evening hours
throughout the weekend as the seabreeze pushes inland. At the
moment, model soundings do not indicate anything severe taking
place, however isolated chances of strong to severe storms are
always possible in the summertime. The main concern will be
localized heavy rainfall on Saturday and Sunday as model
guidance showcases slow storm motion. Thus, any storm that
trains over an area for an extended period of time might cause
localized flash flooding. Heading into Monday, this upper-lvl
ridge will build into the region from the north and allow for a
drier airmass to take over and the chance for precipitation will
decrease to less than 20% (with highest chance across Southeast
Georgia). Expect highs reach into the low to mid 90s, with heat
indices staying under Heat Advisory Criteria.

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
This aforementioned weak low will meander offshore through
Tuesday, before it becomes absorbed by likely then Hurricane
Erin as it passes to the east of the region, remaining
comfortably well offshore, and becomes almost parallel to the
coastline by the middle of the week. Even though Erin will
likely remain well offshore, we will still experience impacts
from the system. A large swell associated with Erin will likely
cause a long period of dangerous surf and rip currents as early
as Monday. Otherwise, high pressure will build into the region
and allow for precipitation chances to be close to normal, or
below normal for this time of the year. Another cold front could
potentially approach the region by the end of the week.

&&

.AVIATION /04Z FRIDAY THROUGH TUESDAY/...
15/06z TAF Discussion:
KCHS/KJZI/KSAV: VFR will prevail through 06z Saturday. Scattered
showers/tstms are expected to develop near KCHS and KJZI by
early afternoon. TEMPO groups for MVFR conditions in TSRA were
included 18-21z at KJZI and 19-22z at KCHS to account for tstm
impacts. Tstm chances look lower at KSAV, but some activity will
be around the terminal. VCTS was highlighted 20-23z to trend.

Extended Aviation Outlook: Brief flight restrictions possible
at all terminals with afternoon showers/thunderstorms.

&&

.MARINE...
Waterspouts: Conditions could favor the development of
waterspouts this morning. Coastal RAP soundings show waterspout
indices reaching well into the 50s by daybreak, which is
solidly in the moderate risk category. Non-supercell tornado
parameter values are rather elevated over the coastal waters
this morning. If this trends continue, a Marine Weather
Statement may be issued prior to sunrise to alert mariners to
the potential for waterspouts.

Through Tonight: There are no concerns with a typical summer
flow in place. Speeds will remain less than 15 kt with seas 2-3
ft. Thunderstorms cloud cluster near the beaches and Charleston
Harbor later this afternoon/evening. Gusts >34 kt, frequent
cloud-to-water lightning and reduced vsbys in moderate to heavy
rainfall could occur. Special Marine Warnings may be needed.

Saturday through Wednesday: High pressure will prevail over the
local waters through early next week, yielding sub-advisory
conditions. Expect north-northeasterly winds at 10 to 15 kts. It
could become quite gusty along the coastline in the afternoon
as the sea breeze pushes inland. Expect seas 2 to 3 ft over the
weekend, but then build to 4 to 6 ft overnight on Monday as the
swell from likely then Hurricane Erin mixes into the marine
zones. It`s possible seas will build 6 to 8 ft on Wednesday as
Erin will be its closest, still remaining comfortably well
offshore, to the region then. Erin will likely cause a long
period of dangerous surf and rip currents as early as Monday.
Small Craft Advisories will likely be needed for all marine
zones on Monday night as seas begin to ramp up then. Also, High
Surf Advisories will likely be needed on Wednesday as 8 footers
start creeping into surf zones.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Heat Advisory from 11 AM this morning to 6 PM EDT this evening
     for GAZ101-116>119-137>141.
SC...Heat Advisory from 11 AM this morning to 6 PM EDT this evening
     for SCZ047-048-051.
MARINE...None.

&&

$$