Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 270535
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
135 AM EDT Tue Jul 27 2021

.SYNOPSIS...
Weak low pressure will drift north along the southeast Georgia
and South Carolina coast tonight and Tuesday. A trough will
then bring unsettled weather through midweek. A weak front
could drop into the region late week and stall over the
weekend.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
The surface low looks to be near Jesup, Georgia, with an
associated inverted trough from that feature northeast into
South Carolina. the low will lift toward Savannah as the trough
meanders in place. Given an abundance of moisture and MLCAPE of
1500-2000 J/kg, we anticipate scattered showers and isolated
thunderstorms to spread north across the eastern third of the
forecast region. this is where we find the best moisture
convergence aligned with the best lapse rates and some upper
difluence.

Given the south and southeast synoptic flow and elevated dew
points, it`ll be much warmer and very humid overnight. Lows
will only reach the mid to upper 70s, and around 80F in Downtown
Charleston/immediate coastline.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH THURSDAY/...
A surface trough of low pressure will linger over the region through
midweek. Aloft, a broad trough will persist over the Northeast with
a large ridge over the Central U.S. Models indicate PWats will surge
to near or over 2.25 inches Tuesday into Wednesday, before gradually
decreasing Wednesday evening. These values are well above late July
climatology. With aid from weak shortwave energy, scattered to
numerous showers and thunderstorms are expected to develop. Coverage
will peak in the afternoons when instability is greatest, but
activity will be possible just about any time including overnight.

Given the deep moisture and fairly weak storm motions, there will be
a threat for locally heavy rainfall which is backed up by some
probabilistic guidance including the HREF. Slow moving storms could
lead to minor flooding in low-lying and poor drainage areas. The
severe threat looks to be low overall, but a couple stronger to
possibly severe storms can`t be ruled out, with the main hazard
being isolated damaging wind gusts.

Moisture levels will be much lower on Thursday and with lack of
large scale forcing, shower/thunderstorm coverage is expected to be
less than previous days. Perhaps the more interesting forecast note
of the day will be the temperatures. Highs are expected to average
in the low to mid 90s, highest inland, with heat indices around
105.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Surface troughing will linger inland on Friday before a weak front
drops into the region and possibly stalls in the vicinity over the
weekend. Mainly diurnally driven showers and thunderstorms are
possible each day. Hot temperatures and higher relative humidity
values could lead to heat indices of 105-110. Given our heat
advisory criteria of 110, we will need to monitor the potential for
Heat Advisories, especially on Friday.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
An unsettled pattern will prevail with the 06Z TAFs, courtesy of
overly abundant moisture, sufficient instability and lift
generated from weak low pressure over southeast Georgia, an
associated trough and various meso-scale boundaries.

The first part of the day there is a good chance that MVFR and
possibly IFR ceilings could impact KSAV, due to the proximity of
that terminal to the surface low.

Otherwise, scattered SHRA and isolated TSRA pre-dawn will
increase in coverage during the daytime hours on Tuesday,
leading to occasional SHRA/TSRA impacting not only KSAV, but
also KCHS and KJZI. Temporary flight restrictions and gusty
winds will result, with the best chances currently looking to
occur during the late morning through the mid to late
afternoon.

There will be a lull in convection during the late afternoon and
evening, but with the approach of a short wave Tuesday night,
additional convection can occur, especially at KCHS and KJZI.

Extended Aviation Outlook: Flight restrictions are possible in
showers and thunderstorms through Wednesday.

&&

.MARINE...
Overnight: Weak surface low pressure will lift north across
southeast Georgia. The marine community will be situated on the
western periphery of the sub-tropical ridge, producing south to
southeast winds of 15 or 20 kt. Some of the widely scattered
thunderstorms however will produce wind gusts of 25 or 30 kt.
Seas will average 3-4 ft.

Waterspouts: The SPC Non-supercell Tornado Parameter and the
local Waterspout Index indicate that waterspouts could occur
through at least Tuesday morning.

Tuesday through Saturday: Generally south to southwest winds
expected through late week. Winds are expected to remain below Small
Craft Advisory criteria, although speeds on Friday could be in the
15-20 knot range as the pressure gradient tightens. Seas will
average 2-4 feet.

&&

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

&&

$$

NEAR TERM...
SHORT TERM...ETM
LONG TERM...ETM
AVIATION...
MARINE...


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