070
FXUS62 KCHS 160325
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1125 PM EDT Sun Sep 15 2024

.SYNOPSIS...
Potential Tropical Cyclone Eight offshore of the Southeast U.S.
Coast is expected to move across the Carolinas Monday afternoon
into Tuesday, then possibly across the Mid-Atlantic states by
Wednesday.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
The National Hurricane Center is issuing advisories on Potential
Tropical Cyclone Eight located off the Southeast Coastline. A
Tropical Storm Warning remains in effect for Charleston and Berkeley
Counties.

Tonight: A broad swath of showers will continue to nudge closer to
the local area from the north/northeast, but will struggle to make
much progress south across the Tri-County Area overnight due to dry
air (currently depicted on water vapor imagery) wrapping along the
southern edge of Potential Tropical Cyclone Eight tracking toward
the Carolina Coast. Scattered to numerous showers are possible
across far northern Charleston and Berkeley Counties during the
night with upwards to 1/2 to 1 inch rainfall accumulation should
the main swath of rain/showers reach the South Santee River.

Outside precip, gusty northeast winds will gradually turn north to
north-northwest overnight between high pressure inland and Potential
Tropical Cyclone Eight approaching from offshore. Gusts across the
Charleston Tri-County will generally range between 20 and 30 mph.
However, gusts could be slightly stronger possible on overpasses and
higher bridges. Between cloud cover, showers and gusty winds,
overnight lows will only dip into the upper 60s inland to lower
70s near the coast.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
Monday: The biggest forecast concern for this period remains to be
the developing low center, currently Potential Tropical Cyclone 8,
just offshore in the Atlantic waters. Using the track from NHC, the
system is expected to make landfall somewhere between McClellanville
and Georgetown, SC Monday afternoon. It should be noted that there
is still a fair amount of uncertainty in the track timing and
location. Regardless of whether or not this system becomes tropical
in nature, the expected impacts have not changed. Still expect the
best threat for tropical storm force winds/wind gusts of 40-50 mph
to be over the Marine waters off of the Charleston County coast.
Some tropical storm force wind gusts could also reach the immediate
Charleston County coast. The heaviest amounts of 1-2 inches, with
locally higher amounts, will be possible over extreme northern
Charleston and Berkeley counties, closer to the Santee River. Away
from the coast, winds will be breezy, generally 10-20 mph with some
gusts to near 30 mph. High temperatures around 80 over the
Charleston Tri-county region and lower 80s rest of the region. By
Monday night, using the current NHC track forecast, the cyclone
should be inland, north of the Santee River in SC. Rainfall chances
are expected to decrease from south to north, with chance PoPs
mainly over the northern Charleston Tri-county, then below mention
after midnight. Lows 65 to 70.

Tuesday and Wednesday: Although there remains uncertainty in
the details of where the remnants of PTC8 will be located,
global models show the area to be on the southern periphery of
under a large, closed upper low with the remnant PTC8 circulation
somewhere in the mountain region of the Mid Atlantic. Despite
the upper trough and presence of deep layer moisture, guidance
PoPs continue to be 20% or less for Tuesday and 20-35% for
Wednesday. Expect any convection to be diurnally driven, helped
by afternoon sea breeze. Highs in the lower to mid 80s Tuesday,
and mid to upper 80s by Wednesday. Lows generally mid to upper
60s away from the coast, and around 70s to the lower 70s near
the coast.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Forecast uncertainty is higher than normal for this period. In
general, models indicate the closed upper low over the mid Atlantic,
will open up/weaken and move southward as upper ridging tries to
develop from the Great Lakes, southwest to the lower MS Valley.
Higher values of deep layer moisture within the center of the upper
closed low may move southward into the area, especially by Friday
and Saturday. Also, the upper low moves southward and weakens, a
surface ridge may strengthen over New England and the Mid Atlantic,
which allows low level northeast winds to form over the region. Have
kept slight chance to low end chance PoPs for this period, centered
around the afternoon heating. Highs near to slightly above normal in
the mid to upper 80s through Friday, then possibly cooling to into
the lower 80s Saturday.

&&

.AVIATION /03Z MONDAY THROUGH FRIDAY/...
Periods of MVFR cigs are expected at CHS/JZI/SAV terminals tonight
through 19-20Z Monday while Potential Tropical Cyclone approaches
the Carolina Coast. There is a potential for lower cigs/vsbys at
CHS/JZI with any rain/showers associated with the system passing
nearby. Northeast winds will also gradually turn northwest after
daybreak Monday at CHS/JZI, but remain gusty with speeds up to 20-25
kt at times. Further south, winds will remain around 10 kt or less
at SAV. VFR conditions should then prevail at terminals heading into
evening hours Monday.

Extended Aviation Outlook: Monday night: MVFR CIGs and gusty
winds expected for KJZI and KCHS with periods of showers on the
back-side of the Potential TC8. MVFR conditions for KSAV, but
less breezy wind and lower chances for any showers.

Tuesday through Thursday: return to more VFR condition, with
isolated mainly afternoon showers and possibly a thunderstorm, which
could bring brief flight restrictions.

&&

.MARINE...
Tonight: Hazardous marine conditions will persist across local
waters as a tight pressure gradient occurs between the inland
high and Potential Tropical Cyclone Eight offshore. A Tropical
Storm Warning remains in effect for the Charleston County
nearshore waters as well as the Charleston Harbor. Elsewhere,
Small Craft Advisories remain in effect through the the night
with northeast winds between 20-30 kt being common along with a
few gusts up to 35 kt at times. Seas will be highest in the
Charleston County waters and offshore Georgia waters, where
seas up to around 10 feet will be possible through tonight.
Elsewhere, seas will mostly be in the 5-8 ft range.

Monday and Monday night: Main forecast concerns continues to be the
progression of now Potential Tropical Cyclone 8. Despite whether or
not this system becomes tropical in nature, we are not expecting any
change in our previous thinking of winds/seas. Tropical storm  force
wind gusts will continue over AMZ350 and near the mouth of
Charleston Harbor, possibly through Monday afternoon. High end SCA
conditions the rest of the waters. By Monday night, the NHC track
takes the storm inland, which should begin the gradual decrease in
winds and seas. Winds may fall below highlights by Monday night all
waters, but seas could stay AOB 6 feet beyond 20 nm offshore through
Tuesday morning.

Later Tuesday through Friday: No highlights expected with generally
south-southwest winds of 15 kts or less and seas 2 to 4 feet,
highest beyond 20 nm. A surface front may move into the waters
Friday, which could switch winds to north-northeast and increase to
10-15 kts, but uncertainty moderate to high for this portion of the
forecast.

Rip Currents: The combination of strong northerly winds and
increasing swell from Potential Tropical Cyclone Eight just offshore
will result in a High Risk of rip currents at all beaches through
the day Monday.

High Surf: Breaking waves are expected to peak around 3-5 ft
tonight at Southeast South Carolina beaches, where a High Surf
Advisory remains in effect into Monday morning. Georgia beaches
should see breakers shy of 5 feet, peaking around 3-4 ft, which
does not meet the criteria for a High Surf Advisory. Due to a
combination of elevated water levels and powerful breaking
waves, significant beach erosion is likely, especially along
east and northeast facing beaches.

&&

.TIDES/COASTAL FLOODING...
Charleston and Coastal Colleton Counties: The tide forecast
becomes a bit more uncertain Monday as predicted tide levels
peak while winds turn more north/north-northwesterly with time
as Potential Tropical Cyclone Eight moves closer to the coast,
then north of the region by late Monday afternoon. For now,
minor coastal flooding is possible during the Monday morning and
evening high tide cycles, but further adjustments are likely.
Later this week, the risk for at least minor flooding will
continue as elevated tides persist.

Beaufort County, SC, south to McIntosh County, GA: The tide
forecast becomes less clear on Monday as water levels will be
fighting northerly winds. For now, levels were kept just below
minor flood levels Monday. Waters levels could be close to
minor flood levels later this week as onshore winds return, but
should largely remain below.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...High Risk for Rip Currents through Monday evening for GAZ117-119-
     139-141.
SC...Tropical Storm Warning for SCZ045-050-052.
     High Risk for Rip Currents through Monday evening for SCZ048>051.
     High Surf Advisory until 8 AM EDT Monday for SCZ048>051.
MARINE...Tropical Storm Warning for AMZ330-350.
     Small Craft Advisory until 11 PM EDT Monday for AMZ352.
     Small Craft Advisory until 5 PM EDT Monday for AMZ354.
     Small Craft Advisory until 1 PM EDT Tuesday for AMZ374.

&&

$$

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