359
FXUS62 KCHS 160732
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
332 AM EDT Mon Sep 16 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 /THROUGH TONIGHT/...
Today: The forecast is closely tied to the track and strength
of Potential Tropical Cyclone Eight. The current NHC forecast
track brings the center of PTC8 inland as a Tropical Storm early
this evening near Georgetown. As far as rainfall goes, the
majority of the precip associated with PTC8 will be confined
very close to the center of circulation. This will limit
rainfall primarily to Colleton County and the Charleston Tri-
County region through the day, with the best chance of more
significant rainfall amounts right along the Santee River. A few
isolated showers could spread west of this envelope at times,
but will be very light as far as amounts go. Regarding rainfall
totals, far eastern Berkeley and eastern upper Charleston County
are the areas where amounts will likely be in the 0.50-1.00"
range, with locally higher amounts right along the Santee River.
The limiting factor will be the dry air on the west and
southwest flank of the system which will keep rainfall coverage
and rates down. Winds will gradually back through the day as the
center of PTC8 gains latitude. Northerly winds in the morning
will become more northwesterly by the early afternoon.
Thankfully, we will definitely be on the weak side of the system
which will reduce impacts from winds. It will be another gusty
day, with the strongest gusts across southeast South Carolina in
the 20-25 mph range. Across southeast Georgia, 15-20 mph will
be more common. The potential for Tropical Storm force winds
will be confined to far eastern Berkeley and upper Charleston
County. Cloud cover around PTC8 and the north to northwest winds
will keep temperatures well below normal for this time of year.
Highs across southeast South Carolina are forecast to be in the
mid to upper 70s, and low 80s for southeast Georgia.

Tonight: The center of PTC8 is forecast to track to the north-
northwest across the Pee Dee region. As it does, the potential
for additional rainfall will end and the bulk of the overnight
is expected to be dry. Skies will start to clear out on the
backside of the system as well as winds steadily turn more
westerly with time. Lows are forecast to reach the mid to upper
60s.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
Tuesday: The remnants of PTC8 will be moving inland towards the
NC/ SC border or Charlotte, NC. As this occurs, weak NVA (or
subsidence) will set in across coastal SC and GA with a
pronounced 300/ 500 MB dry slot. This will keep the area dry
Tuesday, and therefore have removed all mention of precipitation
for the area. Highs Tuesday will actually be near normal thanks
to the proximity of the mid- level low pressure with 1000/ 850
MB thicknesses forecast to be only around 1400 m. Mostly mid 80s
are expected. Temperatures will fall into the upper 60s/ lower
70s, but with dewpoint depressions only a few degrees it will
feel humid overnight.

Wednesday: A weak mid-level low will be centered across the
Mid- Atlantic states and be slowly moving east during the day.
The 500/300 MB dry air that was in place Tuesday, will be a
thing of the past on Wednesday with saturation occurring at all
layers of the atmosphere. The day will likely start of dry with
partly cloudy skies. By the afternoon, the atmosphere will
destabilize and with plentiful moisture have expanded the chance
PoPs across coastal GA with slightly lower chances towards the
Charleston metro (less forecast instability). Synoptically, the
region is on the divergent side of the trough axis, but just
barely. Either way, this would favor neutral to weak forcing for
ascent and given the air mass, a return of afternoon showers
and thunderstorms appears the way to go. High temperatures will
also recover into the mid to upper 80s as thicknesses respond to
the filling mid-level low (1000/ 850 MB thicknesses rise to
1410 m). Low temperatures Wednesday night will again be in the
upper 60s to lower 70s.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
The unsettled weather pattern will continue in the long term as
a mid-level low remains overhead and slowly fills. Global
guidance is in general agreement with the mid-level low slowly
being absorbed by Friday as a mid-level ridge amplifies across
southeast Texas. By next weekend though, the GEFS/ GEPS/ and EPS
start to rapidly diverge. Taking a look at the cluster analysis
shows a fair amount of spread between ensemble members. As of
now, guidance is showing two potential solution sets. The first,
is the mid-level ridge amplifying enough to actually wave break
causing another weak rex block to form next weekend. The
second, is that the mid-level ridge doesn`t amplify as much with
the overall long wave pattern just progressing east. Analyzing
the current synoptic pattern would favor the second solution or
some type of hybrid.

Either solution will keep slight chance PoPs in the forecast
Thursday and Friday as the mid-level weakness remains. Expect
high temperatures slightly above normal or in the mid to upper
80s with lows around 70 degrees.

Saturday into Sunday, the forecast for the solution set with
the potential rex block is wetter and cooler for the weekend.
The forecast for the the more progressive solution is drier and
warmer for the weekend. The reason for this is that if a Rex
Block forms, the mid-level low will remain overhead with another
wedge of high pressure sliding down east of the Appalachians.
As this occurs, precipitation would help to reinforce the CAD
with highs below normal. In the more progressive solution, the
mid-level low would exit the region with weak subsidence on the
backside. As this happens, the wedge would be relatively weak
allowing temperatures to warm with little in the way of
precipitation. For now, have split the difference between the
two solutions.

&&

.AVIATION /08Z MONDAY THROUGH FRIDAY/...
At the start of the 06z TAF period, most of the area is VFR
though there are some MVFR ceilings out there as seen on
satellite. Periods of MVFR ceilings are expected at KCHS and
KJZI, with periods of light rain and drizzle expected as well.
MVFR ceilings will likely arrive later at KSAV, timed into the
TAF at 10z. Through the day, KCHS and KJZI will likely see more
persistent MVFR conditions with some light rain still around in
the morning. The afternoon is expected to be mostly dry at the
TAF sites with VFR conditions in the afternoon. Winds will
remain gusty, with frequent gusts into the 20-25 knot range.
Wind directions will start off the period northeast or north-
northeast, but will gradually turn to become more northwest and
west-northwest by the end of the TAF period.

Extended Aviation Outlook:
Tuesday: VFR with no precipitation forecast.

Wednesday: Prevailing VFR. A return of afternoon showers and
thunderstorms is forecast which could temporarily restrict cigs
and vsbys.

Thursday and Friday: Morning MVFR cigs possible with prevailing
VFR in the afternoon. A few afternoon showers and thunderstorms
is possible which could temporarily restrict cigs and vsbys.

&&

.MARINE...
Today through Tonight: PTC8 will track to the northwest this
morning just outside the local South Carolina waters and is
forecast to move onshore early this evening. For most of the
local marine area, the worst conditions are likely occurring
right now and through the next few hours as the pressure
gradient is enhanced between the inland high and the circulation
around PTC8. Wind speeds and associated seas will then steadily
improve through the day and overnight. The only exception to
this will be the far eastern portion of the Charleston County
waters which will be closest to the center of PTC8. The Tropical
Storm Warning remains in effect for the Charleston County
waters and the Charleston Harbor. Elsewhere, Small Craft
Advisories are in effect. The southern South Carolina waters and
the nearshore Georgia waters are set to end at midnight, and
the outer Georgia waters continue through the night.

Tuesday through Friday: No headlines forecast as the pressure
gradient remains weak across the waters. Generally expect
southwest winds around 10 kts in the morning and then backing
from the southeast around 15 kts in the afternoon. Seas 2 to 4
ft. A weak cold front might cross the waters on Friday.

Rip Currents: The combination of strong winds and swell
associated with PTC8 will result in a High Risk of rip currents
at all beaches today. Long period swell and onshore flow will
again result in a High Risk of rip currents at all area beaches
Tuesday.

High Surf: Breaking waves are expected to peak around 5 ft this
morning along the southeast South Carolina beaches and the High
Surf Advisory remains in effect through 8am. Elsewhere,
conditions will be rough but with a lesser breaking wave height
along the southeast Georgia beaches. Also, due to the
combination of elevated water levels and breaking waves,
significant beach erosion is likely.

&&

.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 this evening for GAZ117-119-139-
     141.
SC...Tropical Storm Warning for SCZ045-050-052.
     High Risk for Rip Currents through this evening for SCZ048>051.
     High Surf Advisory until 8 AM EDT this morning for SCZ048>051.
MARINE...Tropical Storm Warning for AMZ330-350.
     Small Craft Advisory until midnight EDT tonight for AMZ352-354.
     Small Craft Advisory until 1 PM EDT Tuesday for AMZ374.

&&

$$

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