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030
FXUS62 KCHS 221142
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
742 AM EDT Sat Jun 22 2024

.SYNOPSIS...
Tropical Low pressure will move onshore along the Southeast
Georgia coast today. A typical summertime pattern with diurnal
convection is expected next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
Satellite imagery and radar data reveals the tropical low
center has nudged slightly inland into Glynn/Camden counties
with a couple of pronounced feeder bands arcing from the outer
Georgia waters into southeast Georgia up to around the Savannah
River entrance. Convection has displayed an uptick over the
last few hours with a corridor of lightning just outside the
outer waters. SPC mesoanalysis continues to show MLCAPE values
running 1-2K J/Kg in the coastal waters, a small core of >40
knots effective bulk shear near the eastern flank of the low,
and a small core of high values of non- supercell tornado
parameter. Still keeping an eye out for any signs of waterspout
development as we head into the morning hours.

High- res guidance suggest the tropical low will edge inland a
bit today while weakening, although meander up the coast through
tonight. Precip chances with the low and rainfall amounts are
the main forecast challenges.

Today: Primary focus for showers is looking to largely remain
through the coastal areas of southeast Georgia and just into
coastal areas of South Carolina through the early-mid morning
hours. But with heating, inland and a northward expansion of
showers and some thunderstorms is anticipated later this morning
and into the afternoon. Forecast will feature the highest
overall precip chances and rainfall amounts across coastal
southeast Georgia into a portion of coastal southeast South
Carolina where, given the elevated PWAT values/envelope of deep
moisture with the low and potential for training convection,
rainfall amounts of 1 to 2 inches is a good bet through today.
HREF precip probabilities do suggest roughly a 30-50 percent
probability of 3 inches along portions of the coast south of
Savannah. However, no hydro related products are anticipated at
this time. Highs today will range from the upper 80s to the
lower 90s...tempered a bit along the coast by passing
convection.

Tonight: Diurnally driven/enhanced convection should diminish.
However, remnant tropical low will continue to meander up the
coast and may drive additional showers and some thunderstorms
up through the SC coastal waters, some of which might skirt the
South Carolina coastal areas. Forecast will feature chance to
likely pops along the coast with diminishing precip chances
inland. Some locally heavy rainfall will remain a possibility
right along the SC coast. Lows tonight dip into the lower to
middle 70s.
-- End Changed Discussion --

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY/...
Sunday: A weak mid-level Low will be located just offshore in the
morning, quickly getting absorbed into the overall flow. Meanwhile,
troughing will develop over the East Coast, especially to our north.
Surface High pressure will be centered near Bermuda while troughing
persists over the Southeast. Deep moisture will continue to persist
across the region. PWATs across our area should exceed 2", which is
above the 90% mark for CHS per SPC Sounding Climatology and nearly 2
standard deviations per NAEFs. The synoptic models and long range
CAMs indicate an active convective pattern. Therefore, we have
likely POPs across our coastal counties in the afternoon, aided by
the sea breeze. POPs will decrease in the evening and overnight,
with most areas becoming dry after midnight. There is decent
instability, so we can`t completely rule out a stronger or
marginally severe thunderstorm with damaging winds. However, the
bigger concern is the potential for locally heavy rainfall
underneath the thunderstorms. This is due to the abundant moisture
and weak steering flow. So flooding in low-lying and poorly drained
areas is possible. Highs will range from the upper 80s at the
beaches to the lower to mid 90s further inland. Additionally, heat
indices should peak in the lower 100s before convection develops.
Lows will mostly be in the mid 70s.

Monday: The mid-levels will consist of a trough initially over the
East Coast. It`ll gradually shift offshore as time progresses.
Meanwhile, broad High pressure centered over the Southern Plains
will creep it`s way towards our region. At the surface, troughing
will be over the Southeast in the morning, with High pressure in the
Atlantic. A cold front will approach from the north, reaching just
north of our area late at night. The deepest moisture appears to get
pushed offshore in advance of the front, with the 2+" PWATs off our
coast. However, PWATs ~1.75" will remain across our area. The heat
should be the main concern due to 850 mb temperatures, low-level
thickness values, and compression ahead of the front. Highs could
peak in the mid to maybe upper 90s, except cooler at the beaches.
But dew points rising into the 70s near the coast will cause heat
indices to rise to ~105 degrees. This is just short of Heat Advisory
criteria. Additionally, afternoon convection is expected to quickly
develop along the sea breeze and ahead of the approaching front.
This will lower temperatures and heat indices. We have chance POPs
in the afternoon. While a stronger storm with gusty winds is
possible just about anywhere, the bigger concern will be the
potential for locally heavy rainfall underneath the thunderstorms.
Though, steering flow should be a little stronger, which would limit
QPF if no training develops. Convection will gradually decrease
during the evening and overnight. Lows will generally be in the 70s.

Tuesday: Mid-level troughing offshore will shift away as broad High
pressure centered over the Southern Plains tries to make its way
towards our region. A cold front located just to our north at
daybreak should slowly shift southward. It`s expected to stall
across our area and then weaken. The highest PWATs appear to be
located south and offshore of our area. Once again, the heat will be
the main concern. Highs are expected to reach the upper 90s to
around 100 degrees across most of our area, except cooler at the
beaches. Dew points well into the 70s near the coast will cause heat
indices to rise to 105-110 degrees. Coastal Heat Advisories are
possible. But similar to Monday, afternoon convection is expected to
quickly develop, which will lower temperatures and heat indices.
Otherwise, we have chance POPs.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
Weak mid-level troughing will occasionally be over the East Coast.
Surface troughing or weak fronts will be impacting the Southeast
U.S. while High pressure is near Bermuda. This summertime pattern
will yield diurnal convection. The highest POPs are each afternoon
and evening, then trending lower overnight. High temperatures will
be well into the 90s each day. Heat indices could also rise to 105-
110 degrees along the coast Wednesday and Thursday, which could
prompt Heat Advisories.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
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Tropical low pressure near the Altamaha River will drift inland
and weaken today before slowly migrating up the coast tonight.
This will bring rather unsettled conditions to the region,
particularly to the KSAV terminal through a good portion of
today...with periodic MVFR conditions possible. We cannot rule
out the possibility of some thunderstorms impacting the KSAV
terminal, although overall probabilities are not great. TSTMs
have not been included 12Z forecast but will be amended as
needed.

KCHS/KJZI will be a bit less impacted. But shower activity
will increase in and around the terminals this morning and
through the afternoon hours. Brief MVFR restrictions are
possible within any heavier showers. Convection weakens into
tonight. But another round of showers and some thunderstorms may
organize in SC coastal waters later tonight and press into the
SC coastal counties overnight.

Extended Aviation Outlook: Mostly VFR. However, convection will
bring brief flight restrictions, mainly each afternoon and
evening.
-- End Changed Discussion --

&&

.MARINE...
Southeast flow will prevail across the coastal waters today.
Winds may be locally gusty south of the Savannah River, although
gusts and seas will largely remain below Small Craft Advisory
criteria with gusts to around 20 knots and seas 4 to 5 feet.
Winds and seas across the South Carolina coastal waters will run
a touch lower.

Extended Marine: A typical summertime pattern is expected with
High pressure in the Atlantic and occasional surface troughing
over the Southeast. On Sunday sustained winds will mainly be
from the south or southwest. Though, they are expected to surge
from the SW in the evening and overnight. Gusts could approach
25 kt and we can`t rule out Small Craft Advisories for our ocean
zones during this time period. Otherwise, each day expect
gradually backing winds. They`ll be strongest along the land/sea
interface and the Charleston Harbor with the formation of the
afternoon sea breeze. Each night, winds will gradually veer.
Seas will average 2-4 ft.

Rip Currents: Onshore winds and swell energy will keep the rip
current risk elevated today. Depending on the peak winds and
the amount of swell that arrives at the beaches, the local rip
current calculator results in a solid moderate risk and just
below high risk. Will maintain a moderate risk with the morning
forecast at this juncture.

Sunday: Winds will mainly be from the south, with a SE swell
slowly trending lower. This will cause a Moderate Risk of rip
currents to persist for all of our beaches.

&&

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

&&

$$

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