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580
FXUS62 KCHS 181056
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
656 AM EDT Tue Jun 18 2024

.SYNOPSIS...
High pressure will extend across the region early this week. A
trough of low pressure could approach the Southeast U.S coast
by late week.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
The lowest temperatures this morning were as follows:
Walterboro (KRBW)...63F
Ravenel.............63F
Near Huger..........63F

For today: A high amplitude mid and upper ridge will cover much
of the eastern states into the northeast Gulf of Mexico, with
the center near the Mason-Dixon Line with 500 mb heights that
are near 5950-5960 meters. This occurs in tandem with a strong
and humongous sized surface ridge that covers the western
Atlantic and eastern third of the country. there are also hints
that a very subtle inverted trough could form offshore.

The large scale subsidence associated with the ridge aloft, a
pronounced cap around 850 mb, and poor thermodynamics suggest
that convection will be hard to come by. However, a deep
easterly flow, convergence from the sea breeze, some low level
Theta-E ridging, and maybe very weak isentropic ascent will
produce isolated to scattered showers. The best chances will be
over the Georgia coastal counties where the low level
convergence is the best, and PWat is higher than further north.
We did maintain a mention of slight chance thunder since it is
mid June, and the NBM does show isolated coverage this afternoon.
But given weak buoyancy and the HREF indicative of less than
10% chance of t-storms, we would not be surprised if none
actually occur.

There exists a tight gradient around the surf ace high through
the day, and given deep mixing and a boost from the sea breeze,
easterly winds will reach 10-20 mph, and even a little higher
along and near the coast. Gusts will reach as much as 25 or
maybe 30 mph, especially over the coastal counties.

Temperatures will be close to climo, but dew points will be
mainly in the 60s, which equates to afternoon RH`s mainly below
50%. Certainly these are not summerlike values.

Tonight: Little to no change in the pattern both at the surface
and aloft, with even some increase in the strength of both
ridges. A continued deep easterly flow and sufficient moisture
will result in at least isolated showers coming in off the
ocean, especially impacting coastal Georgia. Although winds
diminish inland, they do continue rather gusty near and at the
coast. This will result in a fairly large range of
temperatures; lows 64-68F degrees well inland (where the lowest
dew points are found, and middle 70s on the barrier islands, and
over the Charleston and Savannah metro regions.
-- End Changed Discussion --

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
he local forecast area will remain within the southern periphery
of upper level high pressure centered over New England on Wednesday.
A similar pattern will be present at the surface. The high pressure
at the surface will shift further eastward towards Bermuda on
Thursday and Friday. The high pressure aloft is forecast to remain
over the East Coast through the period. Unseasonably quiet weather
is forecast Wednesday and Thursday as subsidence persists aloft,
with only slight chance to chance PoPs featured in the forecast.
Additionally, thunder chances are rather low as instability is
negligible across the forecast area. Thunder chances have been
capped at slight chance for Wednesday and Thursday.

Friday the pattern turns more active as the subsidence begins to
break down as well as an influx of moisture arrives, originating
from a low pressure disturbance off the east coast of Florida. The
development of the low pressure into anything other than a broad
area of low pressure/open trough is still very low confidence. Most
ensemble guidance continues to suggest little formation. Showers and
thunderstorms are forecast to come ashore Friday afternoon,
increasing in coverage in the afternoon hours. The greatest chances
remain across southeast GA where the greatest moisture profile is.

Temperatures through the period are forecast to be right around
normal, with highs in the upper 80s to around 90 and overnight lows
in the upper 60s to low 70s.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
A broad upper level trough will begin to trek across the southeast
U.S. on Sunday as high pressure aloft shifts further south. At the
surface a cold front will approach the region late this weekend.
Between forcing from the approaching cold front and the local
afternoon sea breeze, precipitation chances are forecast to increase
through the weekend heading into next week. Temperatures will warm
through the period, with low to mid 90s on Saturday warming to upper
90s on Monday.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
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Prevailing VFR conditions are expected at CHS/JZI/SAV terminals
through 12Z Wednesday. However, brief MVFR ceilings are
possible this morning with onshore flow off the Atlantic,
particularly at the SAV terminal.

The risk for any showers, especially at KSAV in the afternoon,
is too low to justify any mention at this time.

Otherwise, gusty easterly winds will peak at least near 20 or
25 kt at the terminals from about 15-16Z through sunset.

Extended Aviation Outlook: Prevailing VFR. Brief flight restrictions
are possible in afternoon showers/thunderstorms Wednesday,
especially at KSAV. Chances of flight restrictions increase at
CHS/JZI/SAV terminals later in the week with showers and
thunderstorms moving onshore.
-- End Changed Discussion --

&&

.MARINE...
Today and tonight: A large and strong ridge of high pressure
will encompass the coastal waters, with maybe a subtle inverted
trough to form nearby. There will be as much as a 2-3 millibar
pressure gradient in place locally, resulting in rather elevated
easterly winds of at least 15 or 20 kt and gusty. The favorable
long duration onshore fetch will allow for seas to reach 4-5
feet within 20 nm today, and 5-6 feet on the outer Georgia
waters. It is there where we have a Small Craft Advisory
beginning early this evening. Seas will build another foot or
so tonight all waters, and we might need to expand the coverage
of the Small Craft Advisories.

Wednesday through Saturday: Generally, high pressure will prevail
across the local marine waters. Northeasterly winds 15 to 20 knots
will persist across the local waters Wednesday 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 will be needed for all
waters outside the Charleston Harbor through Thursday night. Seas
will decrease Friday, with 3 to 4 ft forecast Saturday morning.

Rip Currents: Although there still isn`t much swell that will
impact the beaches today, given the modest onshore winds and
numerous rip currents at Tybee yesterday, and enhanced risk of
rip currents will occur. In combination with the Rip Current MOS
and a locally developed Rip Current Calculator, we are showing
a Moderate Risk of Rip Currents for the South Carolina beaches,
and High Risk for the Georgia beaches today.

A High Risk for rip currents has been hoisted for Wednesday
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: Breaking wave heights could reach 5 ft or greater
Wednesday night into Thursday, especially along the Charleston
County coast. A High Surf Advisory may be required.

&&

.TIDES/COASTAL FLOODING...
With the approaching full moon (6/22) tides in the Charleston Harbor
could reach minor flood stage with the evening high tides both
Wednesday and Thursday. Coastal Flood Advisories could be required
for Charleston and Coastal Colleton Counties.

Tides at Fort Pulaski are forecast to remain below minor flood
stage.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
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GA...High Risk for Rip Currents through this evening for GAZ117-119-139-
     141.
SC...None.
MARINE...Small Craft Advisory from 6 PM this evening to 6 AM EDT
     Saturday for AMZ374.
-- End Changed Discussion --

&&

$$

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