921
FXUS62 KCHS 171744
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
144 PM EDT Sat Aug 17 2024

.SYNOPSIS...
High pressure will remain over the area through most of this
weekend. A cold front will push across the area Sunday night
into Monday. High pressure will then gradually build in from
the north through the remainder of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 140 pM, KCLX detected a line of light showers across
portions of inland GA/SC. This activity may increase later this
afternoon as instability across the region increases. However,
even during peak heating, CAPE values across the Coastal Plain
will range around 1500 J/kg with modest DCAPE. The forecast will
continue to feature SCHC PoPs for showers and thunderstorms
inland. A weak sea breeze is expected to develop during the mid
to late afternoon. Areas along the coast, east of the sea
breeze, should remain dry this afternoon. High temperatures are
forecast to range in the low to mid 90s.

Overnight: The surface pattern will remain fairly static, but
the upper air configuration is forecast to become increasing
cyclonic as the broad mid-level trough becomes reinforced by a
shortwave propagating southeast through the western Ohio Valley.
There are signals in a few of the CAMs that a cluster of
showers could move across the Charleston Tri-County prior to
daybreak Sunday as a bit of channeled vorticity pushes through.
Given HREF means for >0.01" is less than 12% and any activity
would likely occur during/near the diurnal minimum, gridded pops
will remain below mentionable thresholds. Lows will range from
the lower 70s inland to the upper 70s/near 80 at the beaches and
in Downtown Charleston.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY/...
Sunday into Sunday night: A large upper trough will dig into
the Southeast along with a cold front that will slowly approach
from the northwest through the day. The sea breeze is expected
to drift inland during the mid to late afternoon, resulting in
dewpoints to climb into the mid 70s. A broad area of deeper
moisture will push across the area ahead of the front Sunday.
Isolated showers and thunderstorms are forecast to develop
between the sea breeze and the approaching cold front during the
afternoon, with coverage increasing later in the evening.
Temperatures should top out in the low to mid 90s across
southeast South Carolina and mid to upper 90s across southeast
Georgia. Some areas within the coastal corridor could see heat
indices peak at 108 degrees prior to the onset of convection.
Heat Advisories could be needed for a few counties along the
coast. Overnight lows will bottom out in the low 70s inland and
mid 70s along the coast.

Interesting setup across the region Sunday evening. Models
indicate that an MCS will develop across the western Carolinas
Sunday afternoon, then tracking east. The MCS is expected to
reach the forecast area Sunday evening, pushing over the
Atlantic Sunday night. Forecast soundings show SBCAPE values
ranging from 1500-2000 J/kg, with DCAPE values in excess of 1000
J/kg. Hodographs indicate a deep curved profile, with 0-6 km
bulk shear around 30 kt and 0-3 km helicity ranging between
200-300 m2/s2. Strong updrafts look likely with modest mid-level
lapse-rates around 7-8 C/km. This environment should support a
few organized storm clusters, producing swaths of strong to
severe wind gusts and/or large hail. It is possible that a few
supercells may develop ahead of the MCS as well with notable
supercell parameters.

Monday and Tuesday: Aloft, a large trough extending from
extreme eastern Canada down to the Florida Keys will sit nearly
stationary, with the cold front currently timed to reach the
Atlantic coast Monday morning. The forecast looks mostly dry
behind the front both days, with the exception of an isolated
shower/thunderstorm along the coast. Highs will only be a couple
of degrees cooler behind the front, with little in the way of
cold air advection. Low to mid 90s are forecast for most
locations Monday. Overnight Monday, temperatures will drop into
the upper 60s/lower 70s inland and mid 70s along the coast. High
temperatures will be somewhat cooler Tuesday, reaching the
upper 80s to lower 90s.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
The upper trough will lift northeast by mid next week and the
main feature will be strong surface high pressure building in
from the north, forming an inland wedge pattern. Isolated to at
most scattered showers and thunderstorms could develop during
the afternoon and evening hours each day, however modest
subsidence will limit the overall coverage of convection.
Additionally, the sea breeze does not look particular strong
with little land/sea temperature differential. High temperatures
will gradually lower each day, but expected to stay within the
near-normal range; in the mid to upper 80s.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
KCHS/KJZI/KSAV: VFR conditions expected through 18Z Sunday.

Extended Aviation Outlook: A cold front is forecast to impact
the region Sunday evening into early Monday morning, bringing
the risk of brief flight restrictions within showers and
thunderstorms.

&&

.MARINE...
Today: Long period swells from Hurricane Ernesto will dominate
the waters again today. Combined seas will average 6 ft this
morning over the Georgia offshore waters where a Small Craft
Advisory has been extended until 11 am. Seas will subside a bit
today with seas 3-4 ft within 20 NM and 4-5 ft in the Georgia
waters out 20-60 NM. South to southwest winds will back a bit
this afternoon with speeds holding below 15 kt. Dangerous wave
actions will be found at inlets and in/near the entrances of
bays, rivers and harbors today, especially as the out going tide
combines with powerful, incoming long period hurricane swells.
Mariners should use extreme caution. A Marine Weather Statement
has been issued to address these conditions.

Tonight: South to southwest winds will persist with the waters
pinned between high pressure and lee-side troughing the west.
The pressure gradient will tighten a bit overnight, but speeds
look to hold 15 kt or less. Seas could build slightly with a bit
more wind wave possible. Combined seas will average 3-4 ft
within 20 NM and could build to 4-6 ft in the Georgia waters
20-60 NM. Another Small Craft Advisory could be needed for the
Georgia waters beyond 20 NM.

Sunday through Thursday: Winds and seas will increase ahead of
an approaching cold front, which is expected to push into the
local waters Monday and slowly push further into the Atlantic.
Winds will surge from the SW to around 20 kts with gusts up to
25 kt Sunday evening into the overnight period. In addition,
seas could build to around 6ft across portions of the outer GA
waters Sunday. Small Craft Advisories could be needed for
portions of the marine zones. Conditions will improve throughout
the day Monday with seas dropping to 2-4 ft. By Tuesday, winds
will shift out of the northeast with speeds around 10-15 kt.
Another surge is possible Thursday as the pressure gradient
tightening with inland high pressure wedging in from the north.

Rip Currents:
Today: The rip current risk remains in the high category for
today as long periods swells from Hurricane Ernesto will
persist. The rip currents will be especially strong at times
given the power values noted on spectral plots from both the
Edisto (41004) and Grays Reef buoys (41008).

Sunday: Long period swell around 12 seconds from distant
Hurricane Ernesto will continue to impact the Southeast coast
this weekend. A high risk of rip currents are forecast for all
area beaches Sunday.

High Surf: Wave breakers of 4-6 ft will occur along the
Charleston County beaches today as powerful, long period swells
from Hurricane Ernesto persist. A High Surf Advisory has been
posted for the Charleston County beaches through 8 PM.
Elsewhere, breakers in the surf zone will average 3-4 ft with
some 5-6 ft sets possible at Tybee Island, mainly this morning.
Breaking waves of 5+ ft do not look frequent enough to hoist a
High Surf Advisory for Tybee Island at this time.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...High Risk for Rip Currents until 8 PM EDT this evening for GAZ117-
     119-139-141.
SC...High Risk for Rip Currents until 8 PM EDT this evening for
     SCZ048>051.
     High Surf Advisory until 8 PM EDT this evening for SCZ050.
MARINE...None.

&&

$$

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