694
FXUS62 KCHS 171747
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
147 PM EDT Tue Sep 17 2024

.SYNOPSIS...
Low pressure across the Carolinas will weaken through mid week.
High pressure should develop inland late week into the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
Rest of today: No significant changes to the previous forecast.
The region will remain on southern side of a deep, closed upper
low over western NC/eastern TN. Vapor loop shows very dry air
around the southern and eastern side of this upper low. This
should keep a dry forecast in place. Using the latest
temperature trends, have adjusted max temps down a degree or so
over the northern 1/3 of the forecast area. Otherwise, sunny to
mostly sunny conditions to prevail, with highs in the lower to
mid 80s, which is close to seasonal normals. With relatively low
RH values, it will also feel quite comfortable.

Tonight: Closed upper level low will continue to drift across
the southeast region while deeper moisture and associated cloud
cover continues to rotate back into the region leading to overall
partly cloudy conditions. Light winds will allow temperatures to
fall back into the 60s at most locations with temperatures
running a little warmer along the coast.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY/...
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 as the low continues to occlude. The day will start out with
partly cloudy skies and PWATs around 1.9" (between the 75th and 90th
percentile for this time of year). By the afternoon, the atmosphere
will start to destabilize, and with plentiful moisture to work with,
have continued the trend of slowly raising and expanding the chance
PoPs for Wednesday afternoon. Synoptically, the region is on the
divergent side of the trough axis, but just barely. However, the low
is slowly heading east with weak height falls and DCVA over the
area. This would imply weak forcing for ascent, and a return of
afternoon showers and thunderstorms. 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 be in the upper 60s to lower 70s.

Thursday: The barotropic low will begin to open up and become
absorbed by another low over the Canadian Maritimes. As this occurs,
a weak boundary will approach the area from the northwest. A sea
breeze will try to get going, but likely become pinned along the
coast before washing out. Expect high temperatures in the mid to
upper 80s with 1000/ 850 MB thicknesses around 1410/ 1415 m). Low
temperatures Thursday night will be in the upper 60s to lower
70s.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Ensemble guidance has come into better agreement in the extended
period with the GEPS, GEFS, and EPS all showing the mid-level low
slowly exiting the Mid-Atlantic coast this weekend with mid-level
heights rising for coastal SC and GA. This has allowed the forecast
to trend much drier with temperatures near normal.

Friday, the mid-level low will exit the East Coast of the United
States with another wave over the Canadian Maritimes heading east/
southeast. As this occurs, high pressure will slowly build into New
England and ooze down the east side of the Appalachians. Dry
conditions are forecast with highs in the mid 80s and lows in the
mid to upper 60s. Lower dewpoints will also filter into the region
helping to bring down the humidity.

Sunday into Monday surface high pressure will remain in control with
no precipitation expected. Afternoon temperatures will remain in the
mid 80s with lows in the lower to mid 60s. Relative humidity values
will also remain comfortable as dewpoints stay in the 60s.

&&

.AVIATION /18Z TUESDAY THROUGH SATURDAY/...

Rest of today and tonight: VFR conditions are expected to
prevail at all terminals through 18z Wednesday. Some guidance
showing potential for light/shallow fog by sunrise Wednesday,
but latest model soundings look too dry to mention in TAF at
this time. Have introduced Prob30 for light showers late in the
period for KSAV.

Extended Aviation Outlook:

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

Thursday: Morning MVFR cigs possible with prevailing VFR in the
afternoon. A few afternoon showers and thunderstorms are possible
which could temporarily restrict cigs and vsbys. A weak boundary
will cross the terminals late Thursday turning the winds from the
northeast.

Friday and Saturday: Some MVFR cigs are possible early Friday
morning, then VFR through Saturday as surface high builds in from
the north. No precipitation is expected.

&&

.MARINE...
This afternoon through tonight: No significant changes to
previous forecast with no highlights. West to southwest winds
will dominate through today before backing more southerly
tonight. Wind speeds will generally stay in the 5 to 10 knot
range this afternoon and tonight. Seas of 3 to 5 feet are
anticipated rest of today, subsiding to 2 to 4 feet tonight.

Wednesday: Morning showers and thunderstorms will be possible with
winds out of the southeast around 10 kt. Seas 2 to 4 ft.

Thursday: Another round of morning showers and thunderstorms are
possible with a weak boundary crossing the waters Thursday night.
Winds will turn from the northeast around 10 kt. Seas 2 to 4 ft.

Friday: Northeast winds will slowly start to increase in speed 10 to
15 kt as surface high pressure builds in from the north. Wind gusts
of 15 to 20 kt possible, or below Small Craft Advisory criteria.
Seas 3 to 4 ft.

Saturday: Northeast winds 15 to 20 kt with gusts 20 to 25 kt. Seas
around 4 ft. A Small Craft Advisory might be required as the
pressure gradient tightens from building high pressure.

Rip Currents: Lingering swell of around 3 ft every 10 seconds and
astronomical influences from the full moon and perigee will maintain
a High Risk of rip currents for all beaches today.

&&

.TIDES/COASTAL FLOODING...

Evening high tide this evening for Charleston and Colleton
County: Latest guidance and tide trends indicating that the tide
level will reach 7.1-7.3 MLLW at the Charleston gauge. Thus, a
Coastal Flood Advisory will likely be issued later this
afternoon. Tides expected to remain below Coastal Flood Advisory
levels for the rest of our coast southward to the Altamaha
River. As we continue into mid to late week, the risk for at
least minor flooding will continue for Charleston and Coastal
Colleton Counties 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.
MARINE...None.

&&

$$

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