659
FXUS62 KCHS 251340
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
940 AM EDT Tue Jun 25 2024

.SYNOPSIS...
High pressure will remain over the western Atlantic while a
weak cold front approaches the area. This front will likely
linger near the area through mid-week, followed by another
front towards the end of the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Today: 25/13z surface analysis placed a weak southwest-
northeast oriented surface trough/wind shift extending from
Glennville, GA through Springfield, GA and into the Moncks
Corner, SC region. The trough will move little today and may
become a focus for isolated to perhaps scattered showers/tstms
this afternoon. The best focus looks to occur the Colleton-
Dorchester-Berkeley County corridor where the highest 850
theta-e values are progged. Pops 20-30% look on track. Similar
to yesterday, an isolated strong-severe tstm can not be ruled
out with damaging winds and cloud-to-ground lightning being the
primary convective hazards.

Of more concern is the heat. The latest low-level thickness
progs suggest highs will once again push the mid-upper 90s away
from the coast with a greater signal for highs reaching the
century mark across interior Southeast Georgia, possibly
reaching into the Allendale and Hampton areas of South Carolina.
26/05z HREF neighborhood probs show about a 60% chance for
reaching highs 100-102 in these areas, which matches both the
H3R and RAP hourly temperature progs. Highs were nudged up in
this region given this trend. Dewpoints will be key to how high
heat indices will reach. The deeper mixing across the interior
will be fighting the stronger onshore push of higher low-level
moisture noted just off the beaches this morning (dewpoints
already near 80 in spots along the lower South Carolina coast
per 25/13z observations). Models are struggling on exactly
which process will win out. Given dewpoints are already running
higher than what the latest high-res models are depicting,
suspect they may be underplaying the dewpoints across the
coastal corridor this afternoon. Adjusted near term dewpoints
taking trends noted from yesterday support another corridor of
heat indices reaching 105-112 across the coastal counties,
possibly extending into southern portions of Berkeley and
Dorchester Counties. The Heat Advisory looks well placed, but
was expanded to include Inland Berkeley and Dorchester, mainly
to take into account the southern, more urban areas of those
counties where heat indices reaching 108 is the most likely. The
advisory is valid Noon to 6 PM EDT. Some further adjustments to
the advisory may be needed with the noon update, but the
advisory area shows where the highest confidence in reaching
heat indices of 108 to less than 113 is the greatest. Similar to
yesterday, a few instances of heat indices reaching 113+ could
occur, but these do not look widespread enough to justify an
upgrade to an Excessive Heat Warning at this time.

Tonight: Any convection will diminish through the early to mid
evening timeframe with quiet/mild conditions thereafter. Lows
dip into the middle to upper 70s overnight...warmer along the
coast.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
Wednesday: The mid-levels will consist of troughing gradually
developing over the East Coast. At the surface, a weak stationary
front should be located to our west and north at daybreak. It`s
forecasted to dissipate into the afternoon. Though, surface
troughing should remain in place across our region. A cold front
should approach from the northwest overnight. Though, it`s not
expected to reach our area during that time frame. Higher PWATs
should gradually creep into our area as time progresses. It`s
possible they could exceed 2" closer to the coast, which is above
normal for this time of year. The heat will be the main concern due
to 850 mb temperatures, low-level thickness values, and compression
near the front. Highs are expected to reach the mid to upper 90s
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
~108 degrees, which is borderline Heat Advisory criteria. Though,
any could be brief due to afternoon convection lowering the
temperatures. Both the synoptic models and the long-range CAMs have
afternoon convection developing along the inland moving sea breeze.
Scattered coverage seems reasonable, especially further south.
MLCAPEs should approach 1,500-2,000 J/kg across portions of our area
with some shear. With DCAPEs exceeding 1,000 J/kg, a few marginally
severe storms with damaging winds are possible just about anywhere.
Additionally, there will be the potential for locally heavy rainfall
underneath the thunderstorms due to fairly weak steering flow and
the potential for training. Convection should quickly decrease
during the evening, with the overnight being mainly dry. Lows will
be in the 70s.

Thursday: Mid-level troughing initially over the East Coast will
gradually shift offshore. Additionally, a shortwave is expected to
move over our region during the late afternoon or evening. A cold
front located just to our northwest at daybreak should very slowly
move across our area during the day and into the night. There will
be a plume of deep moisture ahead of the front. PWATs could exceed
2", which is above normal for this time of year. Similar to
Wednesday, high temperatures are expected to reach well into the 90s
for most areas, perhaps reaching 1-2 degrees higher. Dew points well
into the 70s near the coast will cause heat indices to rise to ~110
degrees. So Heat Advisories may be needed for the coastal counties.
Forcing from the front, the afternoon sea breeze, and the shortwave
will generate convection in the afternoon. All of the models point
towards scattered to numerous coverage, which is why we have high
end chance POPs. It`s a bit uncertain how much instability and shear
will be in place. But given the setup a few marginally severe storms
with damaging winds are possible just about anywhere. Additionally,
there will be the potential for locally heavy rainfall underneath
the thunderstorms due to fairly weak steering flow and the potential
for training. Convection should gradually decrease during the
evening. But remnant convection could persist everywhere overnight.
Lows will be in the 70s.

Friday: The mid-levels should consist of zonal flow over our region.
At the surface, a stationary front should be over our area in the
morning. It`s expected to dissipate into the afternoon. Deep
moisture will persist across the region. Forcing from the front and
the afternoon sea breeze are expected to generate convection.
Though, the coverage will depend on how much instability is in place
and the amount of shear. Similar to the previous two days, high
temperatures are expected to reach well into the 90s for most areas.
Dew points well into the 70s near the coast will cause heat indices
to rise as high as 108 degrees along the coast, which could prompt
Heat Advisories.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
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. Additionally, heat indices could
approach 108 degrees along the coast each day.

&&

.AVIATION /13Z TUESDAY THROUGH SATURDAY/...
KCHS/KJZI: VFR conditions prevail through the day into Tuesday
night. However, hit and miss showers and thunderstorms are
possible during the afternoon hours although confidence in
coverage/timing and duration is somewhat low. But enough
confidence to include VCSH to the CHS terminal forecast during
the afternoon hours. Brief flight restrictions are also
possible, but will not be included with the 12Z forecasts at
this juncture.

KSAV: VFR conditions prevail through the TAF period. Hit and
miss showers and thunderstorms are possible across southeast
Georgia during the afternoon hours. But confidence in
coverage/timing and duration is too low to include in the
forecasts at this juncture.

Extended Aviation Outlook: Mostly VFR. However, convection could
bring brief flight restrictions, mainly each afternoon and
evening.

&&

.MARINE...
Southwest gustiness lingers along the South Carolina nearshore
waters currently, but will be diminishing over the next few
hours. Small Craft Advisories have been extended out through 6
am to allow for winds and seas to lower. Winds will continue to
weaken through the morning and for the afternoon while backing
southeasterly in time. Seas running 3 to 5 feet early this
morning will subside to 3 feet or less tonight.

Wednesday through Saturday: A typical summertime pattern is
expected with High pressure in the western Atlantic and
occasional surface troughing or fronts over the Southeast. 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, possibly surging closer to the coast. Seas will
be 2-3 ft.

Rip Currents: Wednesday a 1-2 ft SE swell around 8 seconds will be
impacting the beaches. Though, there are hints that an additional SE
swell of 1 ft around 10 seconds could also impact the beaches during
the afternoon. Per internal calculations, this would bump up the rip
current risk to Moderate at all of our beaches. Given the
uncertainty, we opted to maintain a Low risk for now. But this will
need to be reevaluated during the day.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Heat Advisory until 6 PM EDT this evening for GAZ117>119-
     139>141.
SC...Heat Advisory until 6 PM EDT this evening for SCZ044-045-
     047>052.
MARINE...None.

&&

$$