910
FXUS62 KCHS 240916
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
516 AM EDT Tue Sep 24 2024

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

&&

.NEAR TERM /THROUGH TONIGHT/...
Today: Aloft a ridge axis along the Southeast Coast during morning
hours will gradually shift east and further offshore while a large
trough tracks across the Midwest. At the sfc, high pressure
extending south along the East Coast will remain across Southeast
South Carolina and Southeast Georgia for the day. Latest hires
guidance suggests a few showers across the far interior into late
morning where SBCAPE between 500-800 J/kg resides, but large-scale
subsidence and low-lvl moisture advecting further inland throughout
the day suggests much of the area to remain dry by afternoon hours.
With the axis of the mid-lvl ridge shifting further offshore and
modest onshore winds occurring during the afternoon, temps should be
a few degrees cooler than yesterday. In general, high temps should
range in the upper 80s to lower 90s, except near the coast where low-
mid 80s occur due to the onshore wind.

Tonight: The mid-upper lvl ridge continues to shift further offshore
overnight while a large trough digs south across the Midwest and
toward the middle Mississippi River Valley. At the sfc, high
pressure will remain in place and a light southeasterly wind should
prevail for much of the night well ahead of a cold front advancing
across Tennessee and toward the Deep South. Large-scale forcing will
be lacking and dry conditions are expected for all areas, although
some low-lvl moisture is anticipated to return from the south late
and could support some stratus within a few hours of daybreak. Low
temps should range between the low-mid 70s, warmest near the
coast.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
Wednesday: An upper ridge axis will shift over the Atlantic,
meanwhile a large trough/low will position itself over the western
Tennessee Valley. Surface high pressure anchored over northern Maine
and extending southward along the Eastern Seaboard into the
Carolinas will persist, in addition to a developing tropical system
in the southern Gulf of Mexico. A subsidence inversion around the
600-550mb layer noted via model soundings will limit convection,
resulting in mostly quiet weather. Increasing cloud coverage will
occur as the upper trough nears. Highs will reach the mid to upper
80s. Overnight temperatures will be mild as clouds thicken
overnight. in the low to mid 70s most places and near the upper 70s
along the beaches.

Thursday and Friday: We turn the attention to the Potential Tropical
Cyclone 9 (PTC9), in which specific details will depend on the track
and intensity of the system. PTC9 is expected to strengthen fairly
rapidly as it tracks in a general northward direction across the
Gulf of Mexico Thursday. The National Hurricane Center has it
progged to make landfall Thursday afternoon/evening along the
northern Gulf Coast; near/along the Florida Big Bend. Showers are
expected to spread in from the south early morning Thursday, with
potential rainbands associated with the tropical system lifting
northward across the region. These bands could bring rounds of heavy
rainfall, gusty winds reaching tropical storm force or greater, and
the risk for tornadoes. Tropical Storm or Hurricane Watches/Warnings
could be needed for portions of the forecast area.

Conditions will begin to deteriorate further into Thursday night as
the core of the system moves closer to the area. The tropical
cyclone is expected to make its closest approach to our inland
counties late Thursday night/early Friday, as it moves northward
across central Georgia per the latest forecast track. Expect rounds
of widespread heavy rainfall and strong, gusty winds overnight. The
environment also appears to be favorable for fast-tracked tornadoes,
both over land and water. Additional hazards/impacts include
localized power outages and downed trees, along with localized
flooding in areas that experience training rainbands. The system is
forecast to begin to pull north away from the region Friday. We
should begin to see improving conditions by Friday afternoon with
showers becoming less widespread and shifting to the north as drier
air begins to filter in on the backside of the system. Storm total
rainfall amounts are expected to range 2-3 inches across the
Charleston Tri-County area and 3-5 inches for areas west of I-95,
with locally higher amounts possible. Temperatures will generally
peak in the 80s both days.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
As the tropical cyclone rapidly weakens/departs to the north Friday
night, vastly improving weather is expected for the weekend. Winds
will gradually subside, and drier air will filter into the area on
the back side of the system. The upper low will meander over the
Tennessee Valley through the weekend, finally lifting northeast
early next week. With forcing aloft and the return of Gulf moisture,
isolated to scattered showers are possible with 20-30% POPs in place
mainly during each afternoon into early next week. Temperatures will
range near seasonable, in the low to mid 80s for highs.

&&

.AVIATION /09Z TUESDAY THROUGH SATURDAY/...
VFR conditions are expected to prevail at CHS/JZI/SAV terminals
through 06Z Wednesday. However, some shallow ground fog could reduce
vsbys to 6 SM late tonight into early morning.

Extended Aviation Outlook: VFR conditions expected to prevail
through Wednesday. Conditions will begin to deteriorate Thursday as
a tropical cyclone approaches from the southwest. Expect periodic
flight restrictions (MVFR/IFR) Thursday into Friday within rounds of
heavy rain. Wind gusts could reach tropical storm force or greater
Thursday into Friday, with the greatest chances at KSAV. Improving
conditions with a potential return to VFR is possible later Friday
with some lingering gusty winds.

&&

.MARINE...
Today and Tonight: Aloft, a ridge axis along the Southeast Coast
during morning hours will gradually nudge east and further offshore
during the afternoon and overnight period as a large trough digs
across the Midwest toward the middle Mississippi River Valley. At
the sfc, high pressure will extend south along the East Coast and
across local waters through tonight. Given the setup, a weak
pressure gradient is expected across local waters throughout the day
and much of the night, with only a slight enhancement across Georgia
waters late. In general, south winds between 5-10 kt this morning
should top out around 10 kt from the southeast this afternoon.
Overnight, a slight uptick in southeast winds is anticipated, with
10-15 kt wind speeds across Georgia waters. Seas will generally
range between 1-2 ft across nearshore waters and 2-4 ft across
offshore Georgia waters today, but should gradually build a foot
overnight.

Wednesday: Broad high pressure offshore will result in southeast
winds around 15 kt. Seas will average 2-3 ft for the nearshore
waters out 20 nm and 3-4 ft for the outer GA waters from 20-60 nm.
Conditions will begin to deteriorate Wednesday night ahead of an
approaching potential tropical cyclone in the southern Gulf of
Mexico.

Thursday through Friday: Expect dangerous marine conditions as a
northward moving tropical system in the Gulf of Mexico strengthens.
Fine details are likely to change depending on the exact track and
strength of the system. At this juncture, guidance indicates ESE
gusts could range between 25-30 kt by Thursday morning. The tropical
cyclone is expected to track inland and make it closest approach
late Thursday night/early Friday, which is when tropical storm force
gusts or greater are likely across the local waters. Tornadic
waterspouts will also be possible during this time frame, in
addition to bands of heavy rain. Seas are expected to peak between 8-
13 ft within 20 nm and 14-16 ft over the outer GA waters from 20-60
nm late Thursday night. Conditions will begin to improve Friday
night.

Saturday through Sunday: As the tropical system rapidly weakens to
our north, seas will drop to 2-4 ft with westerly winds shifting out
of the north around 10-15 kt.

High Surf and Rip Currents: Breaking waves of 5 feet or greater are
likely to occur at the beaches Thursday into Thursday night. A High
Surf Advisory will likely be needed for all area beaches.
Significant beach erosion is likely to occur during this time.
Additionally, an elevated risk for rip currents is likely Thursday
and Friday with gusty winds, large breakers, and long period
swells.

&&

.TIDES/COASTAL FLOODING...
For today, a Coastal Flood Advisory could be needed during the
afternoon high tide along Charleston and Colleton County coasts with
minor coastal flooding anticipated within 1-2 hours of high tide,
which occurs around 2:12 PM.

Although the astronomical high tides are lowering, minor coastal
flooding remains possible with the daytime high tide cycle along the
Charleston and Colleton County coasts Wednesday.

On Thursday, strengthening onshore winds could lead to an increasing
tidal departure, with some coastal flooding possible along the
Charleston and Colleton County coasts Thursday afternoon. The threat
for coastal flooding is then expected for the entire coast 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...DPB
SHORT TERM...BRM
LONG TERM...BRM
AVIATION...BRM/DPB
MARINE...BRM/DPB