519
FXUS62 KCHS 232100
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
500 PM EDT Mon Sep 23 2024

.SYNOPSIS...
High pressure will linger across the region until mid week. A
tropical cyclone is forecast to move generally northward across
the Gulf of Mexico, then track inland across portions of
Florida, Georgia, and possibly South Carolina.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
The mid-levels will consist of a ridge over the Southeast U.S.
At the surface, broad and relatively weak High pressure will
prevail. The HRRR continues to develop a few showers inland.
Though, each run has them starting and ending later. The earlier
synoptic models and CAMs were indicating these persisting into
the evening and overnight far inland, with perhaps some
strengthening just before daybreak Tuesday. Early evening radar
imagery has been unimpressive so far, and satellite imagery
shows limited cumulus inland. However, west of our area a few
showers have developed. These could move into our area in the
next few hours and/or there could be new development far inland.
Considering all of this, we`re maintaining slight chance POPs
far inland through about midnight. The atmosphere should
stabilize later tonight, which would make it more difficult for
showers to develop and persist. This is why we opted to have no
showers after midnight. Winds away from the immediate coast are
expected to go calm with a mix of clear skies and clouds. This
should yield low temperatures around 70 degrees, and the mid 70s
near the beaches.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
On Tuesday, H5 ridge axis is expected to slide east across the
forecast area during the day. Forecast soundings indicate weak lapse
rates under the ridge, limiting the convective potential. The
forecast will generally remain dry, with SCHC PoPs across portions
of the CHS Tri-county. High temperatures should remain around 90
degrees.

Wednesday, the forecast area will remain under the influence of the
H5 ridge centered over the western Atlantic. At the sfc, high
pressure centered over the Mid-Atlantic States is expected to ridge
south across the region. It is possible that a sea breeze could
trigger isolated showers during the afternoon. However, at this
time, the forecast will remain dry. High temperatures should remain
in the upper 80s.

Thursday: Details of the forecast will largely depend on the
intensity, placement, and timing of Potential Tropical Cyclone (PTC)
Nine sourced from the Gulf of Mexico. See latest NHC Tropical
Weather Outlook for latest information on PTC 9. Based on the
collaborated low position, the center of the system is expected to
reach N. FL by Thursday afternoon. The circulation associated with
the system will remain quite large. In fact, Tropical Storm force
winds could reach the GA waters by Thursday afternoon. GFS and ECMWF
indicates that the leading edge of a rain band will lift north,
pushing across SE GA in the morning, north of the Savannah River in
the afternoon. In addition, onshore winds could lead to an
increasing tidal departure, with some coastal flooding possible with
the high tide Thursday afternoon. It is possible that some excessive
rainfall issues may develop with any heavy rainfall that coincides
with high tide. High temperatures will be limited to 80 to 85
degrees.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Thursday night, PTC 9 will pass between a H5 ridge centered over the
western Atlantic and a closed H5 low over the MississippI River
Valley. PTC 9 should accelerate across FL and GA Thursday night. The
circulation associated with the system will cover the entire
forecast area Thursday night. Given the expected wind fields and
rising values of tropical storm force wind probs, it is expected
that tropical headlines will be needed for portions of the area.

Tornadoes: GFS shows the circulation from the system drawing
instability sourced from the Gulf Stream across SE GA/SC
Thursday night. Forecast soundings show the CAPE across the
coastal counties will surge to 500-1000 J/kg with LI as low as
-5. Interestingly, EHI values along the coast peak between 1-3
units by 6Z Friday. Hodographs indicate a strongly sheared
environment, with 0-1 km SRH in excess of 500 m2/s2. This
environment appears very suitable to fast-tracked tornadoes,
both over land and water.

The system is forecast to begin to pull away from the region on
Friday. Storm total rainfall amounts from the system is expected to
generally range from 3-4 inches, with locally higher amounts.
Ongoing gusty winds combined with the wet ground may result in tree
and power line damage.

The forecast is even more uncertain for Friday night into the
weekend, it is possible that dry air could wrap around the central
CONUS closed low and bring drier conditions to the region. Or, some
guidance indicates that a strong CAD may develop over the region,
with rain, thick cloud cover and cool NE winds. The forecast will
keep scattered convection with day to day highs in the 80s.

&&

.AVIATION /20Z MONDAY THROUGH SATURDAY/...
18Z TAFs: VFR.

Extended Aviation Outlook: VFR conditions expected to prevail
through Wednesday. Gusty conditions are possible at the terminals
during the end of the week. Potential for periodic flight
restrictions are increasing.

&&

.MARINE...
Tonight: Broad High pressure will prevail, yielding tranquil
marine conditions. Expect SE winds 5-10 kt this evening, backing
to the S by daybreak Tuesday. Seas will generally be 2 ft
within 20 nm and 3 ft across the GA waters beyond 20 nm.

Tuesday and Wednesday: Broad high pressure offshore will result in
southeast winds around 10 kt or less on Tuesday, increasing around
15 kts on Wednesday. Seas will average 1-3 ft for the nearshore
waters out 20 NM and 3-4 ft for the outer GA waters from 20-60 NM.

Wednesday night through Saturday, there will be an increase in winds
due to a potentially developing tropical system in the Gulf of
Mexico. Thursday morning, guidance indicates that gusts may range
between 25-30 kts with seas build to 5-6 ft within 20 NM and 8-9 ft
across the outer GA waters. Tropical Storm conditions expected late
Thursday afternoon until Friday morning. Seas are expect to peak
between 10 to 13 ft within 20 NM and 14-15 ft over the outer GA
waters Thursday night.

Conditions will gradually improve late Friday through Saturday.

High Surf and Rip Currents: Five foot breakers are possible at the
beaches Thursday night. Additionally, an elevated risk for rip
currents is likely Thursday and Friday with gusty winds, large
breakers, and long period (10 second) swells.

&&

.TIDES/COASTAL FLOODING...
Although the astronomical high tides are lowering, minor coastal
flooding is expected with the daytime high tide cycle along the
Charleston and Colleton County coasts Tuesday, and potentially
Wednesday.

Strengthening onshore winds could lead to an increasing tidal
departure, with some coastal flooding possible with the high tide
Thursday afternoon.

This threat is expected to continue through the end of
the week due to impacts from a tropical cyclone.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.

&&

$$

NEAR TERM...
SHORT TERM...NED
LONG TERM...NED
AVIATION...NED
MARINE...NED