433
FXUS62 KCHS 161747
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
147 PM EDT Mon Sep 16 2024

.SYNOPSIS...
Potential Tropical Cyclone Eight is expected to move onshore
north of our area tonight into Tuesday, then possibly across
the Mid-Atlantic states by Wednesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Rest of Today: The NHC took a hard look at the forecast for PTC8
for our area. The end result is they dropped the Tropical Storm
Warning for our two impacted counties (Charleston and Berkeley).
Even with its current track north of our area, the impacts
continue to lower. We lowered the POPs further across the
Charleston Tri-County. Arguable, chance POPs are too high in
some spots. But we`re trying to keep some coordination with our
neighboring offices. Likewise, QPF was drastically lowered. This
is due to more dry air working in from the south and west.
Winds will gradually back through the day as the center of PTC8
gains latitude. We did issue a Lake Wind Advisory for Moultrie
for wind gusts through late this afternoon. Otherwise, gusty
winds will gradually lower through late this afternoon. 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 /18Z MONDAY THROUGH SATURDAY/...
Through this evening: KCHS and KJZI: guidance indicating
the potential for MVFR CIGS to hang on through the evening,
possibly rising to VFR after midnight. Have kept MVFR through
about 06/07Z, then trended into VFR. Gusty NW winds through
about 23z this evening. KSAV: Periodic MVFR CIGS through about
sunset, then expect VFR to prevail.

Later tonight/After midnight: Feel VFR conditions will prevail
all three sites.

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...
This afternoon through Tonight: The NHC is forecasting PTC8 to
track to the northwest into this afternoon, staying just north
of our waters. It`ll move onshore early this evening, continuing
to move inland north of our area overnight. Conditions have
improved a bit from early this morning. However, both winds and
seas will remain elevated due to an enhanced pressure gradient
between High pressure inland and the circulation around PTC8.
Winds and seas will continue to trend lower into late afternoon,
this evening, and overnight.

As for headlines, once the NHC dropped the Tropical Storm
Warning for our land areas, we were were able to quickly do the
same for AMZ350. While the NHC has a sliver of 35 kt gusts
across the northern portion of this zone, we felt that this was
overdone. Realistically, mariners should expect occasional
gusts up to 35 kt across the northernmost portion of this zone
through early this afternoon. This is mentioned in both the CWF
and the MWW. Given this small time and area coverage, we opted
to go with a Small Craft Advisory for this zone through
midnight. No other changes were made to the other ocean Small
Craft Advisories. Though, we did add a Small Craft Advisory to
the Charleston Harbor for the next few hours due to wind gusts.

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.

&&

.TIDES/COASTAL FLOODING...
Charleston and Coastal Colleton Counties: The tide forecast
becomes a bit more uncertain today 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 this afternoon. For now, this
evening`s high today could very briefly touch minor coastal
flooding. As we continue into mid to late week, the risk for at
least minor flooding will continue due to high astronomical
tides with the full moon on September 17th.

Beaufort County, SC, south to McIntosh County, GA: Waters
levels could be close to minor flood levels later this week as
onshore winds return.

&&

.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.
     Lake Wind Advisory until 6 PM EDT this evening for SCZ045.
MARINE...Small Craft Advisory until 6 PM EDT this evening for AMZ330.
     Small Craft Advisory until midnight EDT tonight for AMZ350-352-
     354.
     Small Craft Advisory until 1 PM EDT Tuesday for AMZ374.

&&

$$

NEAR TERM...RFM
SHORT TERM...Haines
LONG TERM...Haines
AVIATION...Haines
MARINE...Haines