016
FXUS62 KCHS 061112
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
712 AM EDT Sun Sep 6 2026

.WHAT HAS CHANGED...
The Aviation section has been updated for the 12 TAF issuance.

&&

.KEY MESSAGES...
- 1) Numerous to widespread thunderstorms are expected to
  impact southeast Georgia and southeast South Carolina this
  afternoon and evening. These thunderstorms will bring a risk
  for damaging wind gusts as well as locally heavy rainfall and
  flooding.

- 2) Hot and humid conditions expected again today.

- 3) The potential for coastal flooding will increase beginning
  Monday and persist through the middle of the week.

&&

.DISCUSSION...
KEY MESSAGE 1: Numerous to widespread thunderstorms are
expected to impact southeast Georgia and southeast South
Carolina this afternoon and evening. These thunderstorms will
bring a risk for damaging wind gusts as well as locally heavy
rainfall and flooding.

The forecast continues to focus on the potential for widespread
thunderstorms to produce severe weather and heavy rainfall this
afternoon and evening. Overall, the setup is unchanged from
previous forecast cycles as thunderstorms are expected to
develop just to our north across the SC Midlands and then
progress southward ahead of an upstream cold front.

Severe Weather: The environment ahead of these thunderstorms
should be conducive to maintaining the storms and perhaps even
strengthening. Temperatures will warm into the mid 90s today and
we expected to see MLCAPE values in excess of 2,000 J/kg. Model
soundings also suggest DCAPE values upwards of 1,000 J/kg,
supporting the potential for damaging wind gusts. There should
even be ~20 kts of deep layer shear which could be enough to
support some organization in the form of multi-cell clusters.
Hi-res guidance is still mixed on exactly where the biggest
severe weather threat will be, and will likely be highly
dependent on exactly where convective initiation takes place
upstream. Once storms do get going and propagate to the south,
the progression and interaction of outflow boundaries will play
a notable role in the areas at the biggest risk of seeing severe
thunderstorms.

Heavy Rain: Precipitable water values across the area will be
in the 2-2.25" range and thunderstorms will be very efficient
rainfall producers. We should see hourly rainfall rates of 2+
inches within the strongest storms which will heighten the
locally heavy rainfall and flash flood risk. The 06/00z HREF
shows 30-50% probabilities of 3 inches of rain in a 3 hour
period. So, needless to say, the ingredients for locally heavy
rainfall are present and the question is how quickly do these
storms move through and is there potential for either training
or persistent development. There remains some question as to
what areas are at the biggest risk of seeing the heaviest
rainfall. Overall, model guidance has generally shifted the
focus from around the Charleston metro area to be further south
to be more towards the Beaufort and Savannah areas. But, much
will be determined based on where convective initiation takes
place upstream. The overall risk period will run from the mid to
late afternoon through the late evening hours, depending on how
quickly storms progress.

KEY MESSAGE 2: Hot and humid conditions expected again today.

Today will again bring high temperatures peaking in the mid 90s
across the entire forecast area and even a few upper 90s
possible across portions of southeast GA. Dewpoints are expected
to be in the mid to upper 70s along the coast with low to mid
70s elsewhere. This setup should yield heat indices peaking in
the 105-110 degree range. However, current thinking is that we
will not meet the duration component of Heat Advisory criteria
(108 for 2 hours or more) and overall heat indices will be quite
marginal. Afternoon convection could also be robust and disrupt
peak heating and peak heat indices. Therefore, we will not
issue a Heat Advisory. Fortunately, Sunday will be the last day
with Heat Advisory concerns for the week.

KEY MESSAGE 3: The potential for coastal flooding will increase
beginning Monday and persist through the middle of the week.

Astronomical tides will continue to rise through the middle of
the week thanks to the lunar perigee which peaks today and the
upcoming new moon (9/11). These factors will push astronomical
tides as high as 6.55 ft MLLW at Charleston Wednesday evening,
setting the stage for coastal flooding potential. A cold front
will push through Sunday night and usher in an extended period
of elevated northeast flow through Tuesday which will drive
increased tidal departures. Coastal flooding will be favored
during the evening high tide cycles at Charleston and the Monday
evening high tide looks like the first one that could exceed
the minor coastal flooding threshold of 7 ft MLLW. While minor
coastal flooding is the most likely scenario, the potential for
moderate coastal flooding (7.5 ft MLLW) will increase with the
Tuesday and Wednesday evening high tides as tidal departures
build within the persistent northeast flow. Coastal Flood
Advisories will likely be needed for Charleston and coastal
Colleton counties.

For the rest of the from Beaufort County south including the
southeast GA coast, tidal departures would need to exceed 1 ft
to reach the minor coastal flood threshold (9.5 ft MLLW) at Fort
Pulaski. Therefore, coastal flooding is less likely along this
part of the coast but still can`t be ruled out especially if the
northeast flow behind the passing cold front turns out a bit
stronger than currently forecast.

&&

.AVIATION /12Z SUNDAY THROUGH THURSDAY/...
The 12z TAF period begins with VFR conditions at KCHS, KJZI,
and KSAV. The main forecast issue for this TAF period concerns
thunderstorm potential this afternoon and evening. Storms are
expected to develop north of the area and drop southward toward
the TAF sites through the late afternoon and into the evening.
We have timed thunderstorms into KCHS first around 22-23z,
followed by KJZI around 23-00z, and then KSAV last around
00-01z. There could be isolated storm development ahead of the
later line, but confidence isn`t high enough to account for this
explicitly. These storms will be capable of producing strong
wind gusts, so we have bumped up winds in the PROB30 groups to
include gusts to 30 knots. This could be stronger, but will
depend on if the terminals take a direct hit or not. These
storms should bring at least MVFR conditions with reduced
visibilities due to heavy rain, but at least brief IFR
conditions will be possible as well. Also, at the very end of
the 12z TAF period we could start to see some MVFR ceilings
spread in within the northeast flow. This potential is greater
beyond 12z and will need to be considered with the 18z TAF
issuance.

Extended Aviation Outlook: Showers and thunderstorms could
again impact the terminals on Monday and Tuesday before coverage
diminishes mid to late week. Breezy northeast winds will also
set up along the coast Monday and Tuesday.

&&

.MARINE...
Today through tonight: Winds will turn light and variable this
morning, followed by onshore southeasterly flow this afternoon.
Wind speeds should peak in the 10-15 knot range. The main change
across the local waters will come late tonight when a cold
front drops through from the north. As sunrise Monday
approaches, the surge of northeast flow behind the front will
begin to spread in across the SC waters. Seas should remain in
the 2-3 ft range through the period.

Also of note, thunderstorms are expected to develop inland this
afternoon and evening. These storms could impact the coast and
the coastal waters with strong wind gusts and frequent
lightning.

Monday through Thursday: The surge of northeast flow behind the
cold front will ramp up Monday morning and spread across all
waters through the afternoon. Sustained wind speeds are forecast
to be near 20 knots with gusts around 25 knots across all
waters. These conditions should persist through Tuesday as well.
Small Craft Advisories will almost certainly be needed for all
waters, including Charleston Harbor at times. Seas will ramp up
in response to the northeast surge, with 4-6 feet across much of
the nearshore waters and as high as 6-7 feet across the outer
waters peaking Tuesday. Overall continues will begin to improve
quickly Tuesday night into Wednesday as the gradient weakens.

Rip Currents: Persistent and gusty northeast winds and building
seas will support a Moderate Risk of rip currents at all
beaches along the southeast SC and southeast GA coast on Monday.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.

&&

$$