929
FXUS62 KCHS 300209
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1009 PM EDT Sat Jun 29 2024

.SYNOPSIS...
Atlantic high pressure will prevail this weekend, while a
trough of low pressure resides inland. A cold front will impact
the area Monday Monday into Tuesday before dissipating
offshore. High pressure will return for the latter half of next
week.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
A trough will persist inland, while the Atlantic ridge is across
Florida. In the mid and upper levels of the atmosphere we find
strong ridging almost directly overhead. That along with
nocturnal influences will allow for isolated showers far inland
this evening to completely end come to an end by midnight.
However, there will remain various boundaries through the
night, plus some isentropic ascent and convergence from off the
ocean. In addition, there has been some activity during the
overnight the past two nights. So it`s possible it could happen
again. As a result we hold onto slight chance PoPs far south
through 1 or 2 AM, and isolated activity moving near or onshore
of coastal sections late.

Another very warm and muggy night in store, with lows in the
lower to mid 70s most areas, and upper 70s to around 80 closer
to the coast. Some patchy late night fog possible within areas
that experienced rainfall, but confidence and coverage not
expected to be high enough to put in forecast.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/...
Sunday: The area will be positioned along the far eastern periphery
of an expansive upper-level anticyclone centered over the Central
Plains. A pronounced shortwave is progged to cross eastern North
Carolina late in the afternoon with its tail end crossing eastern
South Carolina during the evening/overnight hours. A cold front will
meander to the southeast during the afternoon hours, but looks to
hold well to the northwest. The airmass south of the front will
remain very moist (dewpts >73 F) and moderately unstable within a
ribbon of PWATs >2 inches. Weak shear (0-6km bulk shear averaging
<10 kt) within a region of little forcing aloft suggest convection
will be mostly airmass driven, only concentrating along mesoscale
boundaries and the inland moving sea breeze. Forcing aloft will
begin to increase a bit by late afternoon and especially during the
evening and overnight hours as the tail end of the aforementioned
shortwave pushes through and the low-level flow becomes somewhat
confluent ahead of a weak frontal wave that develops over the CSRA
into central Georgia. This synoptic setup could delay the greatest
coverage of showers/tstms until the evening hours and before the
onset of slow nocturnal cooling. The temporal distribution of
highest pop were skewed in this direction, averaging 30-50% during
the afternoon (highest inland) with 50-60% during the evening hours.
Convection will slowly wane overnight, but some scattered coverage
could linger well into the early morning hours Monday as the front
approaches and continues to interact with the warm and very moist
environment.

Highs look to reach into the mid-upper 90s away from the coast
before convective initiation occurs. Dewpoints in the mid-upper 70s
could support heat indices of 108-112 with the highest values
occurring along/east of the I-95 corridor. A Heat Advisory has been
issued for areas roughly along/east of an Allendale-Springfield-
Richmond Hill line, including both the Savannah and Charleston Metro
Areas as this areas where confidence in reaching heat indices of 108
are the highest. Far interior Southeast Georgia and locations across
the far south near the Altamaha River looks a bit too marginal for
hitting 108 for a 2nd period advisory. Adjustments to the advisory
area may be needed in later forecast cycles. Lows Sunday night will
range from the mid 70s well inland to the lower 80s at the beaches.

Monday: The approaching cold front will slow down over Southeast
South Carolina and Southeast Georgia Monday as the eastern extension
of the upper high over the Plains erodes and broad troughing occurs
along much of the U.S. East Coast. The setup looks favorable for the
development of numerous to widespread showers/tstms with the front
interacting with a very moist and moderately unstable atmosphere.
PWATs look to surge well into the 2" range within a region of very
weak shear. This will support a somewhat elevated risk for locally
heavy rainfall and localized flooding with even a few instances of
flash flooding being possible. This should help the current D0 and
D1 drought conditions that are in place. Pops were increased to 70-
80% with highs ranging from the upper 80s across Southeast South
Carolina with lower 90s over Southeast Georgia. Overnight lows will
range from the upper 60s/lower 70s far inland to the mid-upper 70s
at the beaches.

Tuesday: The front will meander offshore and hug the coast as it
sags into northern Florida. Drier air will attempt to advect in from
the north, but a good portion of the area looks to hold PWATs >1.5
inches. The best chances for showers/tstms look to occur across the
Southeast Georgia where the deepest moisture and highest instability
will be found. Pops were nudged to 30-70%, highest south of the I-16
corridor, including the Savannah Metro Area. Shear looks to remain
fairly week with slow mean storm motions, so a risk for locally
heavy rainfall and flooding will continues, especially over
Southeast Georgia into far southern South Carolina. It will be
considerably cooler with highs only reaching the mid-upper 80s.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
The front will gradually dissipate offshore by mid-week with high
pressure nosing in from the northeast through much of the period.
Expect a typical diurnal convective pattern to prevail with
shower/tstms mainly concentrating along/ahead of the sea breeze each
day, possibly enhanced by mesoscale boundary interactions. After a
cool start Wednesday, temperatures will return to above normal
levels by Thursday and persist into Saturday.

&&

.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
KCHS/KJZI/KSAV: VFR will prevail through 00Z Monday.

Late tonight and early Sunday there could be isolated convection
near the terminals, most especially at KJZI where we have VCSH
after 09Z.

The sea breeze will be the main mechanism for Sunday. We`ll
include VCSH at KJZI during the late morning/early afternoon as
that boundary moves through. Then VCTS at KCHS and KSAV during
the mid afternoon into the early evening. Brief flight
restrictions with gusty winds could occur in convection,
especially at KCHS and KSAV.

Extended Aviation Outlook: Widespread shower/tstm impacts are
possible Monday afternoon/evening at all terminals. Otherwise,
Brief flight restrictions are possible in showers and
thunderstorms, mainly in the afternoon and evenings through the
period.

&&

.MARINE...
Overnight: No highlights are expected. A ridge of high pressure
at the surface will remain in place to the east and southeast
of the waters. This will keep south-southwest winds of 10 or 15
knots and seas 2 to 3 feet or less. This time of year it is not
uncommon for isolated showers/thunderstorms to redevelop late at
night, and this looks to be the case again.

Sunday through Thursday: Southerly winds will persist into Monday. A
front will sink south into the waters Monday night into Tuesday
resulting in a shift to the east to northeast with a slight uptick
in wind speeds. Winds will return more southerly Wednesday into
Thursday as the front dissipates and high pressure noses in from the
northeast. Winds look to hold below 15 kt through the period. Seas
will average 2-4 ft, except they could build as high as 5 ft Tuesday
behind the front. Widespread showers/tstms will impact the waters
Monday, possibly reducing vsbys to 1 NM or less at times.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Heat Advisory from noon to 7 PM EDT Sunday for GAZ101-116>119.
SC...Heat Advisory from noon to 7 PM EDT Sunday for SCZ040-042>045-
     047>052.
MARINE...None.

&&

$$

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