675
FXUS62 KCHS 251600
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1200 PM 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/...
The heat index has already reached 110 at the Beaufort MCAS, 108
at the Summerville Airport, 107 at the Savannah NWR RAWS just
north of Savannah, 106 at the Charleston Intl Airport, 106 at
the Charleston Executive Airport, 104 in Downtown Charleston,
104 at Hunter AAF and 102 at the Savannah Intl Airport.

No major changes were made for the noon update. The forecast is
mostly on track. GOES-E visible satellite images show a well
defined outflow boundary poised to push onshore along the upper
Charleston County coast soon. This boundary originated from an
area of convection off the northeast South Carolina coast. It is
unclear how this feature will impact both the temperature and
convective pattern later this afternoon, so this will be closely
watched. The surface trough/wind shift has nudged inland ever so
slightly per 1530z observations.

Today: 25/1530z surface analysis placed a weak southwest-
northeast oriented surface trough/wind shift extending from
Glennville, GA through Hampton, SC and into the Santee Cooper
Lakes 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.
25/06z 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 /16Z TUESDAY THROUGH SATURDAY/...
25/18z TAF Discussion:
KCHS/KJZI/KSAV: Best convective parameters look to occur near
KCHS this afternoon in the vicinity of a weak surface trough.
VCTS was highlighted there through 21z. Otherwise, the best tstm
impacts look to remain west of KSAV and KJZI. VFR will prevail
for the remainder of the 18z TAF period. Some last minute
adjustments may be needed based on radar trends at issuance
time.

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

&&

.MARINE...
Today: South to southeast winds 5-10 kt will prevail with seas
2-3 ft. Winds will be a tad higher in the Charleston Harbor.

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.

&&

$$