242
FXUS62 KCHS 191325
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
925 AM EDT Wed Jun 19 2024

...THE RISK FOR FREQUENT AND DANGEROUS RIP CURRENTS CONTINUES AT
AREA BEACHES...

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

&&

.NEAR TERM /THROUGH TONIGHT/...
The forecast is on track and only required slight adjustments
for the late morning update, mainly to increase pops to 40% in
the Edisto Beach-Savannah corridor. RAP soundings still show an
impressive subsidence inversion which holds through the day, so
the risk for tstms is likely too low to justify a mention right
now.

A TUTT located north of Hispaniola will continue to move west-
northwest as it gets closer to the Bahamas late in the day,
while a strong mid and upper anticyclone centered over New
Jersey, Delaware, and Maryland moves little. The immediate area
lies underneath the southern portions of that feature, creating
a very deep easterly flow that extends through at least 300 or
400 millibars. At the surface, a rather tight gradient remains
in place between an extensive ridge of high pressure in the
western Atlantic and much of the eastern states, while
Potential Tropical Cyclone One is found in the southwest Gulf of
Mexico. There will also be a very subtle inverted trough
approaching the local area from the east, while a broad and
slightly better defined trough of low pressure is associated
with the TUTT in a similar surface position.

The deep easterly flow in conjunction with the sea breeze, and
an approaching trough from the ocean will cause isolated to
scattered low-topped showers to occur. We have 20-30% PoPs as
a result. Some higher Theta-E air coming in from the ocean, and
deep moisture convergence will allow for most of the initial
chances across coastal areas of South Carolina this morning,
then into Georgia this afternoon. The lack of buoyancy and a
strong subsidence inversion around 750-800 millibars will negate
the need for any t-storms. This is in line with the HREF and
the SPC Day 1 Convective Outlook.

Deep mixing, the tight gradient, and sea breeze circulations
will cause breezy to windy conditions again throughout. Easterly
winds will reach as high as 15-20 mph far inland, and 25 or 30
mph closer to the coast.

Temperatures will be near or even slightly below climo given
the moderate to strong onshore, reaching the mid and upper 80s
most communities.

Tonight: The TUTT approaches the northwest Bahamas, as it`s
steered by an elongated anticyclone to our north. At the
surface, we again lie underneath strong high pressure centered
southeast of New England, as a surface trough in associated with
the TUTT aloft moves toward the northwest Bahamas. there will
be isolated to perhaps scattered showers within the deep
easterly flow, but any t-storms look to be confined out near
the Gulf Stream where there is a bit more CAPE and instability.
It still looks like many interior places will drop into the mid
and upper 60s with lighter winds developing and a somewhat dry
boundary layer. But with winds remaining elevated near and
along the coast, lows will be at least 5-10F degrees warmer.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY/...
Thursday: Aloft the region will be placed within the southern
periphery of an anticyclone centered over New England. Just off the
east coast of Florida a TUTT will be present. At the surface, high
pressure will build into the local forecast area from the north,
while an inverted trough will be present associated with the TUTT.
Model soundings indicate there will be plenty of subsidence over the
local forecast area, limiting precipitation in the afternoon hours.
PoPs peak Thursday afternoon around 20-30%, with the highest chances
across coastal southeast GA. Instability will be negligible,
therefore have capped thunder probabilities at slight chance. High
temperatures will be around normal, reaching into the upper 80s to
near 90. A stream of moisture associated with the inverted trough
and TUTT will begin encroaching on the forecast area Thursday night
into Friday morning. PWATs around 1 inch on Thursday afternoon could
approach 2 inches by Friday morning. Precipitation chances gradually
increase Thursday night, as more showers are forecast to push
onshore, especially across southeast GA. Overnight low temperatures
are forecast to dip into the mid 60s far inland where conditions
will likely remain dry and cloud free. Along the coastline with
possible showers and increasing cloud cover, temperatures are only
expected to drop into the low to mid 70s.

Friday: The aforementioned stream of moisture will continue to feed
into the forecast area as the inverted trough approaches closer to
the southeastern coast. Aloft the region will remain along the
southern periphery of an anticyclone. Instability Friday looks to be
more supportive of thunderstorms. The best chance for showers and
thunderstorms looks to be along the coastal counties, where PoPs are
around 50-60% in the afternoon. Temperatures are forecast to reach
into the upper 80s along the coast and low 90s further inland.
Overnight lows will remain rather mild, with low 70s inland and mid
to upper 70s along the coast.

Saturday: The anticyclone aloft is forecast to shift further
southward, centered over the southeastern states. At the surface the
inverted trough associated with the TUTT will continue to approach
the local forecast area, however it will likely be in a weakening
state. PWATs will remain around 1.7 inches. Between the inverted
trough and the local sea breeze, isolated to scattered showers and
thunderstorms will again be possible in the afternoon. The highest
chances will remain across southeast GA. Temperatures will begin to
warm on Saturday, with highs in the mid 90s inland and low 90s at
the coast.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
A broad trough aloft will progress from the Great Lakes into New
England, likely staying to the north of the local forecast area. The
forecast area will likely be positioned along the eastern flank of
an anticyclone aloft centered close to TX. At the surface the
inverted trough will dissipate Sunday, however lingering moisture
combined with the local sea breeze will produce isolated to
scattered showers and thunderstorms. The main forecast highlight in
the long term period will be the building heat. Temperatures on
Sunday are forecast to reach in the mid to upper 90s away from the
direct coastline, with close to 90 along the coast. Heat index
values will likely reach from 102-105 with a few locations possibly
around 107-108. The hottest day of the period will be Monday, with
some inland locations pushing 100F. Heat index values are forecast
to reach from 105-108. Heat Advisories may be required for Monday
and possibly for Sunday.

&&

.AVIATION /13Z WEDNESDAY THROUGH SUNDAY/...
KCHS/KJZI/KSAV: While there will be VFR ceilings and the risk
for some light showers at times moving in from the Atlantic, VFR
is forecast at all sites through 12Z Thursday.

Similar to the past two days, gusty easterly winds will occur
from late this morning through about sunset in response to a
tight gradient and deep mixing. Winds will frequently gust to
20 or 25 kt, occasionally even stronger.

Extended Aviation Outlook: Prevailing VFR. Flight restrictions will
be possible at all terminals later in the week with showers and
thunderstorms moving onshore.

&&

.MARINE...
Today and tonight: The local maritime area will be situated
mainly under the control of impressive high pressure centered to
the southeast of New England. There will be as much as about a 3
millibar spread north to south across the waters, leading to
Small Craft Advisories that were already in place over the
ocean. That gradient, plus the interaction of the land/sea
interface will be enough for a Small Craft Advisory also
impacting Charleston Harbor from late morning into at least
early tonight. Winds across all waters will peak around 20 kt
with gusts of at least 25 kt at times, and the very favorable
onshore fetch will cause seas to reach 6 or 7 feet, with even
waves up to 2 feet in the Charleston Harbor.

Thursday through Sunday: Northeasterly winds 15 to 20 knots will
persist across the local waters Thursday into Friday morning. Gusts
may approach 25 knots at times. Winds Friday will remain out of the
NE, however easing slightly to 10 to 15 knots. Conditions will
continue to improve into Saturday, with winds shifting to the SE
around 10 knots by Saturday night. Seas are forecast to build across
the local marine zones, peaking Thursday with 5 to 6 ft across the
nearshore waters and 7 to 8 ft across the 20-60 nm offshore GA
waters. Small Craft Advisories are in effect for all waters outside
the Charleston Harbor through Friday morning. Gusts in the
Charleston Harbor may approach 25 knots, thus requiring a Small
Craft Advisory as well. Seas will decrease Friday, with 3 to 4 ft
forecast Saturday into Sunday.

Rip Currents: There were at least 30-40 rip currents at Tybee
yesterday, most of which were strong. This prompted closure of
the waters to swimming, and it`s likely this will be the case
again today. The agitated surf, strong long shore currents and
the windy conditions will cause strong rip currents at all
beaches. The High Risk has been maintained.

A High Risk for rip currents has also been maintained for
Thursday across all area beaches. An enhanced risk of rip currents
will likely persist through the end of the week as long period swell
impacts the region.

High Surf: Guidance continues to show most breakers of 3-4 feet
at the beaches today, with maybe an occasional 5 footer. This is
not enough to warrant a High Surf Advisory. With similar winds
over the ocean during tonight, the persistent onshore fetch
could allow for 5 foot breakers to become more common, and a
High Surf Advisory could be required.

&&

.TIDES/COASTAL FLOODING...
Tides are already more than a foot above astronomical levels,
and with a continued moderate to strong easterly wind, and the
Full Moon to occur Friday evening, those departures could grow
even more. It`s possible that we could see minor coastal
flooding over the coastal sections of Charleston and Colleton
County with the evening high tides today, Thursday and maybe
Friday.

Tides elsewhere are forecast to remain below minor flood stage.

&&

.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...Small Craft Advisory until 1 AM EDT Thursday for AMZ330.
     Small Craft Advisory until 6 AM EDT Friday for AMZ350-352-354.
     Small Craft Advisory until 11 PM EDT Friday for AMZ374.

&&

$$