274
FXUS62 KCHS 041046
AFDCHS
Area Forecast Discussion
National Weather Service Charleston SC
646 AM EDT Tue Aug 4 2026
.WHAT HAS CHANGED...
The fog key message was removed. The Aviation discussion was
updated for the 04/12z TAFs.
&&
.KEY MESSAGES...
- 1) Another round of scattered to numerous showers and
thunderstorms will impact the region today. Locally heavy
rainfall is possible along with a risk for an isolated strong
to severe thunderstorm.
- 2) A typical summertime pattern returns from midweek through
the weekend, with isolated strong to severe thunderstorms
possible each day.
&&
.DISCUSSION...
KEY MESSAGE 1: Another round of scattered to numerous showers
and thunderstorms will impact the region today. Locally heavy
rainfall is possible along with a risk for an isolated strong to
severe thunderstorm.
Water vapor imagery shows the upper trough to the west has
completely cut off from the main belt of the westerlies and has
closed off into an upper-level cyclone. The upper low is
forecast to meander over northern/central Georgia through
tonight with the local area located along its far eastern
periphery. A large area of dry air observed on moisture imagery
is poised to push in from the southwest later today which will
result in a considerable decrease in PWAT values compared to
the near record levels observed from the past several days,
likely dropping down into the 1.50-1.90" range by this afternoon
(lowest PWATs at the coast, highest far interior Southeast
Georgia). Despite this, modest instability (MLCAPE 1500-1800
J/kg) is still expected to occur with highs warming into the
upper 80s/lower 90s with dewpoints generally in the lower-mid
70s (some upper 70s at the coast in the vicinity of the sea
breeze). MLCAPE values should peak in the 1500-2000 J/kg range
this afternoon. With the upper low holdings to the west, several
around of showers/tstms are poised to impact the region through
tonight.
Round 1: The first round is expected to impact parts of the
Charleston County coast through daybreak. As low-level
convergence builds over the Atlantic near the west wall of the
Gulf Stream within a lingering plume of PWATs 2.25-2.45",
convection is expected to slowly build. A number of the short-
term CAMS suggest convection could consolidate into a fairly
large complex, which could brush much of Charleston County,
especially along/east of the US-17 corridor, including Downtown
Charleston. Given the level of PWATS noted, intense hourly
rainfall rates could occur with 04/00z HREF neighborhood
probabilities for >1"/3-hr running 60-90% and >3"/3-hr 10-30%
(both highest across the middle and upper portions of the
Charleston County coast). Depending on how convection evolves,
will need to watch for a possible short-term flood threat for
this area, especially since will be during the morning commute.
Fortunately, the mean 850-250 hPa steering flow remains in the
20-25 kt range out of the southwest which will keep storms
fairly progressive.
Round 2: Once convection moves northeast of Cape Romain by mid-
morning, dry conditions should prevail. Convection is expected
to initiate by early afternoon across interior Southeast Georgia
where a region of higher 850 hPa theat-e will be found. There
are no discernible impulses forecast to cross the area this
afternoon even with the upper low to the west. In fact, the
main vorticity channel looks to remain displaced well offshore.
This suggests convection will be largely airmass driven with the
evolution of showers/tstms likely being driven by mesoscale
interactions such as convective outflow collisions with the sea
breeze. There are signals the sea breeze could become a large
focus for convection along the I-95 corridor from Walterboro
south to along the Georgia coast by late afternoon as outflow
generated by convection over interior Southeast Georgia
intersects it. Pops 40-70% were realigned slightly to favor
this scenario, highest along the I-95 corridor from KRBW to
near KBQK/KSSI. There will be a risk for locally heavy rainfall,
but rainfall rates will be curtailed somewhat given the lower
PWATs in place this afternoon. The dry air aloft will elevate
the risk for damaging wind gusts, but with such 0-6km weak shear
in place, any strong to severe tstms that form will remain
pulse-like and closely tied to where updrafts can be locally
enhanced by boundary collisions.
Round 3: Similar to the past few nights, nocturnal convection
is expected to blossom over the Atlantic early Wednesday morning
as convergence shifts back closer to west wall of the Gulf
Stream. Some of this activity will likely stream into parts of
the lower South Carolina coast into the Charleston Tri-County
area as the steering trajectories back from southwest to south.
KEY MESSAGE 2: A typical summertime pattern returns from
midweek through the weekend, with isolated strong to severe
thunderstorms possible each day.
As the inland stationary front dissipates Wednesday while the
upper low lifts northeast, Atlantic high pressure will build
westward, placing the forecast area along its western periphery
through the weekend. This pattern will support slightly less
coverage than what has been seen over the last few days, with a
daily round of scattered convection. The sea breeze and any
remnant outflow boundaries will serve as the primary focus for
afternoon and early evening thunderstorm development.
While instability will be somewhat limited Wednesday, gradually
warmer temperatures and persistent moisture will contribute to
a slight increase in instability each day noted by SBCAPE values
rising from 1500 J/kg to 2500-3000 J/kg by Friday. Forecast
soundings indicate DCAPE values of 800-1000 J/kg during each
afternoon and evening period, which could support a few storms
capable of producing damaging wind gusts. Deep moisture, with
PWAT values near 2 inches each day, will make for efficient
rainfall rates with some storms capable of dropping a quick inch
or two of rain. Additionally, slow storm motions averaging 10
kt or so, combined with training or repeated rounds of
convection, could increase the potential for isolated instances
of minor flooding, especially in low-lying and poor drainage
areas.
&&
.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
04/12z TAFs:
KCHS/KJZI: Thunderstorms will remain near both terminals through
14z before exiting to the northeast. KJZI still has the best
chances for direct impacts and a TEMPO group for this was
maintained and extended slightly. Later today, the greatest
coverage of showers/tstms this afternoon look to remain west of
the terminals. Overnight, yet another surge of showers/tstms
moving onshore from off the Atlantic is poised to impact both
terminals. There remains some timing and coverage differences in
the various guidance, so introduced a PROB30 for TSRA from
08-12z to trend for now.
KSAV: An unexpected surge of low stratus moved north of the
Altamaha River a few hours ago and will impact KSAV through mid-
morning. An amendment to include IFR cigs was issued just after
10z and these conditions were maintained for the 12z TAF
package. Cigs may briefly drop below alternate minimums through
14-15z, but as daytime heating builds, suspect prevailing cigs
will remain at or above the critical 600 ft level. Risk for
showers/tstms will increase this afternoon with data supporting
a cluster of storms nearing the terminal by late afternoon along
the sea breeze. For now, a TEMPO group for TSRA was included
21-24z with conditions limited to MVFR. The need for a
prevailing group with possibly lower conditions will reassessed
with later forecast cycles.
Extended Aviation Outlook: Periodic flight restrictions are
expected in showers and thunderstorms this week.
&&
.MARINE...
Through Tonight: Convection early this morning and again
late tonight will pose a risk for mariners. Gusty winds,
locally heavy rainfall with vsbys 1 NM or less and cloud-to-
water lightning are all possible. Otherwise, a southerly wind
regime will linger into tonight. Winds outside of convection
look to remain 15 kt or less, although a few gusts to 20 kt
could occur this afternoon near the beaches and Charleston
Harbor and overnight across all waters. Seas will average 2-4
ft.
Wednesday through Saturday: High pressure in the Atlantic will
be the dominant synoptic feature through the weekend. This will
generate a typical summertime wind field with increased winds
along the land/sea interface each afternoon associated with the
sea breeze. Marine conditions are expected to remain below Small
Craft Advisory criteria through the weekend.
Rip Currents: There is a moderate risk of rip currents for the
Charleston County beaches today due to lingering 2 foot swells
at 7-8 seconds, combined with elevated onshore flow. There is a
low risk for all remaining beaches. Low risk for all beaches for
Wednesday.
Waterspouts: Forecast sounding output and elevated non-supercell
tornado parameters values over the nearshore and offshore waters
look to support a risk for waterspouts this morning. Satellite
and radar already suggest a few cloud lines are trying to
develop over the Atlantic which could become the focus for
waterspouts through late morning. A Marine Weather Statement
was issued to alert mariners to this possibility.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.
&&
$$
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