258
FXUS62 KCHS 181949
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
349 PM EDT Tue Jun 18 2024

.SYNOPSIS...
High pressure will extend across the region this week. A trough
of low pressure will impact the Southeast U.S coast Thursday
into Friday.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
This Evening: Aloft, a large ridge will remain centered across the
Mid-Atlantic and Southeast United States. At the sfc, high pressure
centered across the western Atlantic off the Mid-Atlantic and
Northeast Coast will extend southwest across the local area. The
pattern will favor large scale subsidence across the region and with
drier air depicted on water vapor imagery offshore, should
suppress/limit convection. However, an easterly sfc wind along the
southern edge of the sfc high centered north of the region will help
drive low-lvl moisture onshore and should support few to perhaps
scattered showers into evening hours. An isolated thunderstorm can
not be ruled out as well until sunset.

Overnight, little to no change in the pattern is expected aloft or
near the sfc with high pressure dominating the pattern. Expect any
shower or thunderstorm to wane or diminishing within an hour or so
of sunset, with most areas remaining rain-free through the night.
The only exception could be along the coast of southeast Georgia,
where onshore flow maintains sufficient moisture for a light shower
or two near daybreak. Although winds will diminish inland by late
evening, gusty conditions could persist along the immediate coast.
The pattern will support a fairly large range in temps late, with
lows expected to dip into the mid-upper 60s inland to mid 70s near
the beaches.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...
Wednesday and Thursday: The southern flanks of the expansive upper
level anticyclone centered over the eastern United States will begin
to buckle just a bit as a well defined TUTT located north of the
Greater Antilles approaches the Southeast U.S. coast. The
operational GFS is has finally come in line with the rest of the
global guidance in keep any surface reflection of the TUTT as an
open tropical wave/inverted trough as it moves onshore late Thursday
night into the day Friday. Given a modest northeast low-level flow
is expected to continue ahead of the approaching tropical wave,
steering trajectories favor coastal Georgia for the best chances for
measurable rainfall. Still not seeing a strong QPF signal in the
various guidance for any concentrated areas of showers given the
development of deep convection seems unlikely with the degree of
subsidence noted aloft, but isolated to scattered low-topped showers
with a few tstms appear likely. Pops 20-40% were maintained for
mainly the coastal counties, highest along the Georgia coast. Highs
will warm into the upper 80s/lower 90s away from the coast both days
with lows Thursday morning dropping into mid-upper 60s well inland
to the mid-upper 70s at the beaches. Breezy to locally windy
conditions will also persist along the immediate coast and beaches.

Thursday Night and Friday: Rain chances will begin to ramp up late
Thursday Night and especially Friday as the approaching tropical
waves moves onshore. Shower coverage may lessen a bit Thursday
evening as subsidence ahead of the tropical wave spread in from the
east, but this will rapidly change as daybreak approaches Friday and
the primary wave axis pushes inland. The wave will be accompanied by
a ribbon of PWATS in excess of 2 inches. This coupled with some
forcing with the weakening TUTT aloft and the convergent/east side
of the westward propagating surface wave should be enough to support
scattered if not numerous showers with a few tstms. Pops were
trended up a bit to 40-60% (highest coast), but given the TUTT will
likely be rapidly dampening as it approaches the expansive upper-
level anticyclone, there is some hesitancy to go any higher with
pops at this time. Further adjustments will likely be needed. Lows
Thursday night will drop into the mid-upper 60s well inland to the
mid-upper 70s at the beaches. Highs Friday will range from the upper
80s/lower 90s away from the coast with cooler conditions at the
beaches.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
The tropical wave and associated TUTT aloft will quickly dissipate
over the weekend with the region positioned along the eastern flanks
of the large subtropical anticyclone. Despite the dissipation of the
TUTT, a broad weakness looks to remain through early next week.
This coupled with sea breeze influences and lingering deep-layered
moisture featuring PWATS in excess of 2 inches will support
scattered showers/tstms each day. The heat will also begin to build
through the weekend and especially Monday with highs warming into
lower-mid 90s Saturday with the mid-upper 90s into early next week.
The warmest day looks to occur Monday where a few spots far inland
could make a run for 100 before the onset of showers/tstms.
Dewpoints do not look to really mix out during this period with heat
indices expected to peak 100-103 Saturday, 102-105 Sunday and 105-
110 Monday, highest across the inland portions of the coastal counties.
Heat Advisories could be needed at some point with Monday being
the best day for reaching the Heat Advisory criteria of 108.

&&

.AVIATION /20Z TUESDAY THROUGH SUNDAY/...
Prevailing VFR conditions are expected at CHS/JZI/SAV terminals
through 18Z Wednesday. However, brief showers and therefore brief
MVFR conditions could impact the SAV terminal this afternoon, then
again late morning into early afternoon Wednesday. Otherwise, expect
gusty east winds at all terminals this afternoon (20-23 kt), then
again at a similar speed late morning into the afternoon Wednesday.

Extended Aviation Outlook: Brief flight restrictions are possible in
afternoon showers/thunderstorms Wednesday and Thursday, especially
at KSAV. Chances of flight restrictions increase at KCHS/KJZI/KSAV
terminals Friday and Saturday with lesser chances Sunday.

&&

.MARINE...
Tonight: A large and strong ridge of high pressure will encompass
the coastal waters, with a subtle inverted trough to form nearby.
The pattern will favor an enhanced pressure gradient across local
waters through the night, with easterly winds gusting upwards to 20-
25 kt. Favorable long duration onshore fetch will also allow seas to
build across local waters, eventually peaking between 4-6 ft across
nearshore waters and 5-7 ft across offshore Georgia waters. Small
Craft Advisories will therefore be in effect for all local waters
outside the CHS Harbor tonight, but a brief lull in winds is
possible this evening before 6 ft seas arrive across nearshore
waters around midnight.

Wednesday through Saturday: Gusty northeast winds will persist into
Friday as a tropical waves approaches from the east and a modest
gradient persists over the coastal waters. Northeast winds will
average 15-20 kt with gusts to 25 kt during this time. Seas will
remain above 6 ft through Thursday night within 20 NM and into
Friday evening for the waters 20-60 NM offshore. Small Craft
Advisories are in effect for these waters. Seas look to peak 5-6
nearshore waters and 6-8 ft in the offshore waters, mainly on
Thursday. Winds in the Charleston Harbor will be near advisory
thresholds, but are expected to hold just sky. The need for an
advisory there will be reevaluated Wednesday morning. Both winds and
seas will begin to diminish Friday night into Monday.

Rip Currents/High Surf: Tybee Island Ocean Rescue is flying double
red flags at all Tybee Island beaches where a number of very strong,
dangerous rip currents have been observed. The waters have been
closed here as a result. Expect the risk for strong and dangerous
rip currents to spread into all beaches Wednesday which will persist
into Thursday. A high risk for rip currents is being highlighted for
all beaches for both days. NWPS breaking wave guidance shows
breakers reaching 3-5 ft along the beaches on Wednesday and
Thursday, highest in the Folly Beach area. Given only spotty
instances of 5 ft breakers are being depicted, the situation for
Wednesday looks to marginal for a High Surf Advisory at this time.

&&

.TIDES/COASTAL FLOODING...
Surface high pressure will remain off the coast of New England with
a tight pressure gradient and elevated winds across the South
Carolina and Georgia coast. A full moon on 6/22 will also cause the
astronomical tides to slowly build. There is a chance that minor
coastal flood stage could be reach on the Wednesday and Thursday
evening high tides for Charleston Harbor.

Tides at Fort Pulaski are forecast to remain below minor flood
stage.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...High Risk for Rip Currents through Wednesday evening for GAZ117-119-
     139-141.
SC...High Risk for Rip Currents from Wednesday morning through Wednesday
     evening for SCZ048>051.
MARINE...Small Craft Advisory until 6 AM EDT Friday for AMZ350-352-354.
     Small Craft Advisory until 11 PM EDT Friday for AMZ374.

&&

$$

NEAR TERM...DPB
SHORT TERM...ST
LONG TERM...ST
AVIATION...DPB/ST
MARINE...DPB/ST