430
FXUS62 KCHS 200804
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
404 AM EDT Thu Jun 20 2024

...DANGEROUS LIFE-THREATENING RIP CURRENTS AT THE BEACHES AGAIN
TODAY...

.SYNOPSIS...
High pressure will extend across the region today. A tropical
wave will impact the Southeast U.S coast tonight into Friday.
High pressure will return over the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
Today: A large mid and upper anticyclone ans its associated
ridge will be situated from off the Delmarva in the Atlantic
into the central states. Meanwhile, a surface and low level
ridge is generally in the same locations, while to the south a
tropical wave to the northeast of the Bahamas will move west-
northwest. By evening that feature will be north of the Bahamas
and well east of Cape Canaveral, with central pressures down to
just near 1015 millibars. NHC has designated this system as
AL92, and is showing just a 30% chance of any tropical cyclone
formation.

The large scale subsidence associated with the ridging both
surface and aloft, poor thermodynamics, and considerable dry
air above a capping inversion around 800-850 millibars will
only allow for isolated to scattered low-topped showers. The
best chances are this morning, when the strongest frictional
convergence occurs over the coastal counties. This will also be
yet another day without any t-storms, which is certainly a rare
occurrence for the first day of summer, with the solstice to
begin at 451 PM EDT.

Just like the past few days, it`ll be breezy to windy across the
entire area with a fairly tight gradient between the tropical
wave to the southeast and the ridge to the north. Expect
easterly winds as high as 15-20 mph with gusts of 25 or 30 mph
over the coastal counties, and up to 15 mph with gusts of 20 mph
or a little higher far inland.

The deep onshore flow will hold temperatures near or just below
climo, with the vast majority of the region held down in the
80s.

Tonight: The ridging aloft continues to hold firm, and steers
the tropical wave to a position offshore the Florida northeast
coast between Cape Canaveral and Jacksonville. Moisture
continues to increase, with PWat reaching 1.5 to 2 inches over
eastern sections late. Low level convergence also intensifies
with a 25-35 kt just offshore, and there is a slight decrease
in heights aloft. This will allow for an increasing chance of
convection through the night as the tropical wave draws a little
closer. By morning we show scattered showers over the coastal
corridor, with slight chance PoPs further inland. There is even
MLCAPE in excess of 1000 J/kg near the coast, so we do have
slight chance of t-storms. At this point the QPF for tonight is
mainly 1/4 inch or less. So no flooding concerns.

Winds remain elevated along and close to the coast, but they do
diminish inland from what they were during the daylight hours.
There`s still enough dry air holding on far inland to allow for
lows in the upper 60s. But with the increase in moisture
further east, lows will only drop to the lower and middle 70s.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY/...
Aloft, an anticyclone will be positioned over the Mid-Atlantic to
start Friday. While at the surface Friday morning will begin with an
inverted trough impacting the southeast coastline. This trough will
bring a plume of tropical moisture into the region, with PWATs
hovering around 2 inches through the daytime. Scattered to numerous
showers and thunderstorms will be possible, with the greatest
chances across southeast Georgia. Overall, rainfall amounts look to
amount to 0.25-0.5 inches across the forecast area, so there are no
rainfall/flooding concerns at this juncture. Highs will be right
around normal, reaching into the low 90s inland with upper 80s
elsewhere. Overnight lows will dip into the low 70s inland with mid
to upper 70s along the coastal counties.

Broad mid-level ridging will develop on Saturday and persist into
Sunday, while at the surface the aforementioned inverted trough will
likely linger in the vicinity of the Florida/Georgia border. With
the lingering trough will also be lingering moisture, with PWATs
remaining near 1.8 inches through the weekend. Showers and
thunderstorms will be possible each afternoon, especially across
southeast GA where the moisture will be greatest. Temperatures will
gradually warm through the weekend, with highs in the low to mid 90s
on Saturday and mid to upper 90s on Sunday. Overnight temperatures
will be in the mid to upper 70s.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
A broad trough will progress from the Great Lakes into New England
early in the week. At the surface a cold front will approach the
region, however it will likely be in a weakening state and will most
likely not make a clear passage through the region. Through the rest
of the period conditions will return to a summertime pattern of
afternoon showers and thunderstorms. Temperatures on Monday are
forecast to reach into the mid to upper 90s, with little mixing out
of dew points. Heat index values are forecast to reach around 105F
across most areas, with some locations seeing values around 108F.
Heat Advisories may be required. It is worth noting that potential
convection could disrupt the temperatures.

&&

.AVIATION /07Z THURSDAY THROUGH MONDAY/...
KCHS/KJZI/KSAV: Only a small chance of any showers at the
terminals through Thursday evening. Even if they happen to move
through, no impacts would occur. Showers and a few t-storms
associated with a tropical wave to the south will not reach the
terminals until near the very end of this forecast cycle, or
beyond. As a result we have VFR conditions prevailing, with any
ceilings around 3500 feet.

All sites will experience gusty easterly winds yet again late
this morning into the evening, frequently achieving 20-25 kt,
and occasionally stronger.

Extended Aviation Outlook: Flight restrictions will be possible at
all terminals Friday through the weekend with showers and
thunderstorms moving onshore.

&&

.MARINE...
Today and tonight: A strong high pressure ridge will remain
anchored to the north of the local waters, steering a tropical
wave from northeast of the Bahamas this morning to offshore the
northeast Florida coast by daybreak Friday. The gradient between
these two features will produce solid Small Craft Advisories
over the Atlantic, and also eventually a Small Craft Advisory in
Charleston Harbor. ENE winds will average 20-25 kt with some
higher gusts in the Atlantic, with winds reaching similar
speeds in Charleston harbor from late morning into early this
evening. The favorable fetch will allow for seas as high as 6
and 7 feet within 20 nm, and 8 or 9 feet on the outer Georgia
waters. Waves in Charleston Harbor will be up to 2 feet. Marines
can expect isolated t-storms moving tonight in response to the
tropical wave.

Friday through Monday: An inverted trough will impact the marine
zones Friday, likely lingering into the weekend. Thereafter high
pressure will build into the region. Winds Friday will be out of the
ENE, around 10 to 15 knots. Winds will shift to the SE around 10
knots by Saturday night. Seas are forecast to average 5 to 6 ft
until Friday afternoon across the nearshore waters. Small Craft
Advisories are in effect until Friday afternoon. Across the 20-60 nm
offshore GA waters seas will take a little longer to subside, with 5
to 6 ft persisting into early Friday night. All Small Craft Advisory
conditions should be clear of the forecast area to start Saturday,
with conditions remaining below criteria through the remainder of
the period.

Rip Currents: Conditions at the beaches today is very similar to
the past few days, where we have had several dozen rip currents
(many of them strong) at Tybee Island. So we expect additional
frequent and strong rip currents again today at all beaches,
with the greatest coverage at Tybee.

A High Risk for rip currents has been maintained for Friday
across all area beaches. An enhanced risk of rip currents could
persist into Saturday as long period swell impacts the region.

High Surf: While there can be some occasional 5 foot breakers
in the surf zone today, most breakers will be 3 or 4 feet, so no
High Surf Advisory is required. Even so, some coastal areas
will experience erosion.

&&

.TIDES/COASTAL FLOODING...
Tides continue running more than a foot above astronomical
levels, and with a continued moderate to strong east and
northeast wind, and the Full Moon to occur Friday evening,
those departures could grow even more. It is possible minor
coastal flooding could occur over the coastal sections of
Charleston and Colleton Counties with the high tide this
evening. Tides elsewhere are forecast to remain below minor
flood stage.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...High Risk for Rip Currents through this evening for GAZ117-119-139-
     141.
SC...High Risk for Rip Currents through this evening for SCZ048>051.
MARINE...Small Craft Advisory from 11 AM this morning to 8 PM EDT this
     evening for AMZ330.
     Small Craft Advisory until 7 PM EDT Friday for AMZ350-352-354.
     Small Craft Advisory until 11 PM EDT Friday for AMZ374.

&&

$$

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