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551
FXUS62 KCHS 210834
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
434 AM EDT Fri Jun 21 2024

...LIFE-THREATENING RIP CURRENTS AT THE BEACHES AGAIN TODAY...

.SYNOPSIS...
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A tropical disturbance will approach the Southeast coast late
today, then shift inland tonight. High pressure will then become
the primary weather feature into the middle of next week.
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&&

.NEAR TERM /THROUGH TONIGHT/...
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Today: The long anticipated approach of a tropical disturbance
in the Atlantic is finally arriving, with the center of the NHC
designated AL92 located about 200 miles east of Jacksonville.
It`s very possible that this system could become a tropical
depression as it continues to move west-northwest, and it gets
close to the northeast Florida of southeast Georgia coasts late
in the day. Whether it is a disturbance or a depression, the
weather impacts to the local area will be the same: increased
convection, gusty winds (especially near the coast), a High Risk
of rip currents, and minor beach erosion.

Tropical-like PWats that near or even greater than 2 inches
will move in from the east. This along with more MLCAPE than
recent days will allow for scattered to numerous showers
initially over the nearby Atlantic to move ashore during the
mid or late morning and afternoon. We have PoPs up to 50-70%,
with the greatest chances along the coastal counties, most
especially southeast Georgia. By late day the coverage of the
showers diminishes, as the best coastal convergence starts to
weaken. We reduced the previous forecast of t-storms to isolated
or scattered, mainly because there isn`t much buoyancy, and
only limited simulated lightning depictions per various models.
There is no risk for severe weather.

QPF still looks to be 1/2 inch or less, with the potential for
locally higher amounts where t-storms occur. However, the lack
of rain for many places the past 10 days or so, suggests that
there is little to no risk for any flooding concerns.

Winds will again be breezy due to the persistent northeast-east
flow to the north of the tropical disturbance (or depression),
and a modest gradient between that feature and high pressure to
the north and northeast. Winds though won`t be as strong as
recent days, with gusts mainly less than 15 mph far inland, but
up to 15-25 mph over the coastal corridor.

Temperatures are a bit tricky given the greater coverage of
convection. But given the long daylight of this first full day
of summer, and 850 mb temperatures that are near 16-17C, we`re
showing highs mainly in the mid and upper 80s. Parts of the
region near and west of US-301 will reach 90-91F degrees.

Tonight: The remains of the Atlantic low will move into
southeast Georgia as an open wave of trough. Elevated PWat and
continued coastal convergence will allow for at least isolated
to scattered showers and a few t-storms. The higher PoPs and
greater QPF will be in closer proximity to the remains of the
surface low. There is some evidence of low stratus forming over
our northwest tier late, and perhaps resulting in some patchy
fog. Lows will be a little warmer than recent nights with
higher dew points and more of a southeast synoptic flow.
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&&

.SHORT TERM /SATURDAY THROUGH MONDAY/...
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Saturday: The mid-levels will consist of broad High pressure over
the Lower MS Valley, and a weak Low just offshore. The Low will
shift towards the Southeast coast and weaken, pushing the High
further to the west. At the surface, a remnant Low may be over or
near our area in the morning. Though, it`s expected to transition
into a trough over the Southeast by the afternoon. Additionally,
High pressure will be over Bermuda. There will be deep moisture
across the region from the remnant Low. 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. Both the
synoptic models and long range CAMs point to an active summertime
pattern. Expect likely POPs across our GA counties in the afternoon,
aided by the sea breeze, and chance POPs across our SC counties.
POPs will decrease in the evening and overnight, but remain in the
chance category along the coast. We can`t completely rule out a
marginally severe thunderstorm with damaging winds. But the bigger
concern will be the potential for locally heavy rainfall underneath
the thunderstorms, especially given the weak steering flow and
potential for training. Highs will be in the upper 80s to lower 90s.
Lows will generally be in the 70s.

Sunday: A weak mid-level Low offshore in the morning will get
absorbed into the overall flow. Meanwhile, troughing will develop
over the East Coast. Surface High pressure will be in the Atlantic
with weak troughing over the Southeast. Deep moisture will persist
across our area with PWATs exceeding 2". This remains well above
normal for this time of year. Another active afternoon is expected
with likely POPs across most of our area. Similar to Saturday, we
can`t completely rule out a marginally severe thunderstorm with
damaging winds. But the bigger concern remains the potential for
locally heavy rainfall underneath the thunderstorms due to the weak
steering flow. The convection will decrease in both coverage and
intensity during the evening and overnight. Highs will range from
the upper 80s at the beaches to the lower to mid 90s elsewhere.
Additionally, heat indices should top the 100 degree mark before
convection develops. Lows will generally be in the mid 70s.

Monday: The mid-levels will consist of a trough over the East Coast,
gradually shifting offshore. 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 during the day. 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 may be a bigger concern with rising 850 mb
temperatures and compression ahead of the front. Highs could peak in
the mid to upper 90s, except cooler at the beaches. But dew points
well into the 70s could cause heat indices to rise to 105-110
degrees, which could prompt coastal Heat Advisories. However,
afternoon convection is expected to quickly develop, which would
lower temperatures. This aspect of the forecast will need to be
refined further.
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&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
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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 forecast generally has POPs
peaking in the afternoon and evening, then gradually transitioning
them to favor the Atlantic coastal waters during the overnight
hours. High temperatures will be well into the 90s. Heat indices
could also rise to 105-110 degrees along the coast, which could
prompt some Heat Advisories.
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&&

.AVIATION /07Z FRIDAY THROUGH TUESDAY/...
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KCHS/KJZI/KSAV: No concerns through about 12-13Z, then some
showers will start to develop as the tropical disturbance in the
Atlantic gets closer. Eventually the showers will become more
scattered or numerous in coverage, with even the risk of a few
t-storms. Brief flight restrictions can certainly occur in any
of the convection, but for now we show VFR weather. The showers
and t-storms will decrease in coverage late day/early evening,
but a few could still linger into tonight as the remnants of the
disturbance are found near the Florida-Georgia border.

All sites will experience gusty easterly winds today, but less
than recent days.

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

.MARINE...
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Today: A tropical disturbance centered about 175 miles southeast
of Savannah early on, reaches close to the coasts of Georgia and
Florida late in the day. There might be just enough time for
this system to become a Tropical Depression, but no more, given
considerable dry air impeding its developing. There remains a
decent gradient in place between that system and elongated high
pressure to the north. Enough so that we still have Small CRaft
Advisories on all Atlantic waters, for E-NE winds of 15-20 kt
and gusts nea5 25 kt. Seas are still elevated after several days
of a persistent onshore wind, and are as high as 6 feet within
20 nm of shore, but up to 8 feet further out. Charleston Harbor
won`t have as much wind as recently, but still up to 15 or
occasionally 20 kt. Mariners can expect isolated to scattered
t-storms developing today in response to the tropical system.
While conditions are not extremely favorable for waterspouts
per an in-house Waterspout Index, given Non-Supercell Parameter
values between 1 and 3 units out near the Gulf Stream early this
morning, this is something that will need to be watched for
possible isolated waterspouts.

Tonight: The tropical low will become an open wave or trough as
it moves into southeast Georgia. The gradient eases, and we`ll
start to see winds and eventually seas come down enough where we
can drop the Small Craft Advisories.

Extended Marine: A typical summertime pattern is expected with High
pressure in the Atlantic and occasional surface troughing over the
Southeast. By Sunday, sustained winds will mainly be from the south
or southwest, strongest along the land/sea interface with the
formation of the afternoon sea breeze. Seas will average 2-4 ft.

Rip Currents: Persistent onshore flow and lingering elevated
seas will again produce a High Risk of rip currents at all
beaches today. Lifeguards continued to indicate hazardous
swimming conditions at area beaches, and these conditions are
expected to continue today.

Saturday: Winds will stay onshore, but seas will trend lower.
Therefore, we have a Moderate Risk of rip currents for all of
our beaches.
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&&

.TIDES/COASTAL FLOODING...
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Tide levels will continue to be elevated late this week thanks
to persistent onshore flow and elevated seas. However, the
astronomical tide values aren`t particularly high, which will
reduce the overall coastal flooding risk. The high tide this
evening (~8:30 pm) in Charleston Harbor will likely fall short
of when shallow coastal flooding begins.
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&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...High Risk for Rip Currents through this evening for GAZ117-119-139-
     141.
SC...High Risk for Rip Currents through this evening for SCZ048>051.
MARINE...Small Craft Advisory until 4 PM EDT this afternoon for AMZ350-
     352.
     Small Craft Advisory until 7 PM EDT this evening for AMZ354.
     Small Craft Advisory until 11 PM EDT this evening for AMZ374.

&&

$$

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