367
FXUS62 KCHS 131500
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1100 AM EDT Tue Aug 13 2024

.SYNOPSIS...
A cold front will move slowly south into the area today, then
pass through on Wednesday. High pressure will build from the
north into late week, before giving way to a cold front early
next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Late this morning: Surface analysis shows that the weak boundary
that has been lingering across the Southeast for the last few
days is currently draped across the forecast area, running along
the Charleston County coast, down through Beaufort and inland.
We have already seen isolated convection this morning near the
front, mainly to the northeast from around Georgetown up through
the Grand Strand. This boundary should serve as the focus for
convection through the rest of the day, bringing a threat for a
few strong storms and locally heavy rainfall. Given the subtle
nature of the boundary, hi-res models are struggling to paint a
consistent picture for convective placement and overall
coverage. Current thinking is that convection will first develop
along the Charleston County coast, essentially beginning now
and continuing into the early afternoon. Attention then turns to
convection further inland, likely sourced from outflow
associated with ongoing storms across the South Carolina
Upstate. This activity should consolidate across the Midlands
later this afternoon, and then drop southward into the Tri-
County and the rest of the Lowcountry into the evening hours.

The severe potential will be aided by some stronger mid-level
flow on the southern extent of the belt of west-southwest flow
across the Appalachians and into the Mid-Atlantic. This should
provide around 25 knots of bulk shear and with DCAPE values
approaching 800-1,000 J/kg, we will see a damaging wind gust
potential.

The locally heavy rainfall threat will also persist thanks to
precipitable water values hanging around in the 1.80-2.00" range
and the lingering on the ground vulnerability due to heavy
rainfall last week.

Convective coverage will be less the further southwest you go,
so we are advertising less coverage for our southeast Georgia
areas. Temperatures should be on track to reach the low to mid
90s for southeast South Carolina, and mostly mid 90s for
southeast Georgia. We should again see an area of lower dew
points across interior southeast Georgia, but dew points should
pool along the Georgia coast and up into southeast South
Carolina. Heat index values could reach 110 degrees along the
Georgia coast, up through Beaufort and Edisto Beach. A Heat
Advisory remains in effect. Elsewhere, heat index values around
105 will be more common.

Tonight: Coverage of convection will diminish through the
evening hours, although sitting along the southern flank of
upper level troughing, high-res guidance does suggest that some
shower activity might linger into the overnight. A bit cooler
overnight than in recent times, with lows in the lower to middle
70s...upper 70s along the coast.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
Wednesday: The mid and upper trough is situated over the
eastern states, as a 5940 meter anticyclone amplifies over the
central region. The resulting northwest flow between these two
large scale features will allow for a weak and slow moving cold
front to drop through the local counties. The front will be near
or just south of the area by late in the day. There remains
sufficient moisture, instability, and even some shear to
generate scattered PoPs, greatest over southeast Georgia with
the interaction of the sea breeze with the front. There is also
some additional forcing for ascent in response to a subtle short
wave moving through. maybe that`s enough to produce some
isolated strong or marginally severe storms with DCAPE in excess
of 1000 J/kg. Max temperatures will be a bit lower given breezy
onshore winds and a subtle change in air mass moving in.

Thursday: The ridging aloft to our west is somewhat less
amplified, but the east coast trough does persist, maintaining a
northwest flow. the cold front will be to the south, as high
pressure builds in from the north, and Tropical Cyclone Ernesto
is east of the Bahamas. PWat is quite low for this time of year,
down under 1.5 inches, and there is little in the way of
instability. We`ll show slight chance PoPs over Georgia along
the sea breeze, mainly to account for slightly better moisture.
However, its is certainly possible that it`ll be rainfree all
locations. It`ll certainly be a noticeable change in the air
mass, with max temperatures mainly in the 80s, and even some dew
points down into the 60s with a continued onshore flow.

Friday: Flat ridging prevails aloft, while at the surface, high
pressure persist overhead, and Tropical Cyclone Ernesto is
heading toward Bermuda. We should be able to get by with yet
another rainfree day, with limited moisture and the lack of
forcing. Max temperatures will be very similar to those on
Thursday, with many places again showing dew points down in the
60s.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
A full latitude trough takes shape across the area over the
weekend into early next week, which not only lifts Ernesto off
much further into the northern Atlantic, but also sends a cold
front into closer proximity from the northwest at some points
late in the forecast period. With warmer temperatures and a
return of more typical moisture, convection will also return.
We`ll go slight chance/chance for now, but given the potential
for better shear, these values might be on the conservative
side. temperatures will warm back into the 90s for all areas
away from the beaches.

&&

.AVIATION /15Z TUESDAY THROUGH SATURDAY/...
KCHS/KJZI/KSAV: Scattered convection will develop after 18Z at
all three sites as the interaction of the sea breeze and a weak
cold front occurs in the area. Better chances for convection
will occur at CHS and JZI and tempo groups for TSRA have been
included with the 12Z terminal forecasts from 20Z through 23Z.
Any convection that directly impacts a terminal could produce
brief MVFR conditions and gusty winds.

Coverage of convection diminishes this evening. However, there
are signals that spotty shower activity could continue to impact
CHS and JZI through the night.

Extended Aviation Outlook: Wednesday: Brief flight restrictions
possible at all sites, mainly with afternoon/early evening
convection. The chances for more prolonged flight restrictions
might be at KSAV with a cold front closer by.

Thursday and Friday: Less than 15% chance for convection, with
VFR expected to prevail as deep layer dry air tries to push
southward through the region.

Saturday: Maybe a chance of diurnal convection trying to
return.

&&

.MARINE...
Weak surface boundary has already pressed into the SC coastal
waters and will continue to slip southward through the day into
tonight. Winds will (or have) turn north/northeastward behind
the boundary through tonight but largely remain 10 knots or
less. Seas will run 3 feet or less.

Wednesday through Thursday: Fairly decent winds across the
marine area as a cold front sags slowly southward Wednesday and
gives way to high pressure from the north by Thursday. NE winds
will reach a solid 15-20 kt and gusty, and although there could
be some gusts around 25 kt at times, the duration and coverage
at this stag e don`t look to be enough for a Small Craft
Advisory.

Friday through saturday: Tropical Cyclone Ernesto will be
turning northward as it reaches our latitude, but is found out
close to Bermuda during this time. Our local gradient steadily
slackens as weak high pressure prevails. That said, some 6 foot
seas associated with the tropical cyclone could make it into the
outermost Georgia waters, and we might require a Small Craft
Advisory if this occurs.

Rip Currents: For now we`ll keep a Low Risk of rip currents at
the local beaches Wednesday. However, if winds and/or swells are
any higher than now forecast, the risk might be higher. There
is likely an enhanced risk of rip currents late this week, as
swells from distant Tropical Cyclone Ernesto impact the beaches.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Heat Advisory until 6 PM EDT this evening for GAZ117>119-
     139>141.
SC...Heat Advisory until 6 PM EDT this evening for SCZ047>049-051.
MARINE...None.

&&

$$

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