666
FXUS62 KCHS 131150
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
750 AM EDT Tue Aug 13 2024

.SYNOPSIS...
A cold front will move slowly south into the area today, then
pass through on Wednesday. High pressure will build from the
north into late week, before giving way to a cold front early
next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
A bit of stratus has managed to expand across portions of
southeast SC over the last few hours, which will erode by mid to
late morning. Sky forecasts have been updated to reflect that.
Otherwise, no changes were made to the going forecast.

Previous discussion...
Suppressed upper level heights extend down through the mid
Atlantic and into the Carolinas with a mid level short-wave
sliding southeastward out of the Ohio Valley toward the mid
Atlantic region. Some semblance of a boundary extends off the
Atlantic and cuts across the central part of the forecast area,
with weak northeasterly low level flow across northern third of
the CWA early this morning. Quiet weather inland for the time
being with a touch of stratus lurking through the SC lowcountry
(in the vicinity of the boundary) and a few showers outside the
SC outer waters.


Today: Weak/remnant boundary and axis of higher dewpoint/theta-E
air will linger across the region through the day. The combination
of daytime heating/destabilization in the presence of modest
larger scale forcing for ascent along the southern periphery of
the upper level trough and smaller scale boundaries...should
kick off showers and thunderstorms along the coastal corridor
and back through the SC midlands this afternoon into this
evening. Forecast will feature scattered to numerous precip
chances with the highest chances from the Midlands down through
the SC Lowcountry.

A slightly better setup for strong to severe storms anticipated
this afternoon into this evening, particularly across southeast
South Carolina. Afternoon heating will drive MLCAPE values into
the 1500-2500 J/Kg range with an axis of higher dewpoint air
and instability stretched out across the southeast SC counties
into the Atlantic...but diminished instability down through
southeast Georgia with slightly lower dewpoint air wrapping into
that region. Belt of stronger mid-level flow (500 mb winds
around 30 knots) will reside across the mid Atlantic into the
Carolinas resulting in slightly elevated effective bulk shear
values and 1-2 units of Supercell Composite Parameter,
suggesting the potential for better organized updrafts and a
marginal risk for severe storms across the SC counties.

Meanwhile, one or more rounds of thunderstorms moving through
the SC Lowcountry could produce locally heavy rainfall and
potentially cause hydro issues given elevated rivers/creeks and
wet soils.

Tonight: Coverage of convection will diminish through the
evening hours, although sitting along the southern flank of
upper level troughing, high-res guidance does suggest that some
shower activity might linger into the overnight. A bit cooler
overnight than in recent times, with lows in the lower to middle
70s...upper 70s along the coast.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY/...
Wednesday: The mid and upper trough is situated over the eastern
states, as a 5940 meter anticyclone amplifies over the central
region. The resulting northwest flow between these two large scale
features will allow for a weak and slow moving cold front to drop
through the local counties. The front will be near or just south of
the area by late in the day. There remains sufficient moisture,
instability, and even some shear to generate scattered PoPs,
greatest over southeast Georgia with the interaction of the sea
breeze with the front. There is also some additional forcing for
ascent in response to a subtle short wave moving through. maybe
that`s enough to produce some isolated strong or marginally severe
storms with DCAPE in excess of 1000 J/kg. Max temperatures will be a
bit lower given breezy onshore winds and a subtle change in air mass
moving in.

Thursday: The ridging aloft to our west is somewhat less amplified,
but the east coast trough does persist, maintaining a northwest
flow. the cold front will be to the south, as high pressure builds
in from the north, and Tropical Cyclone Ernesto is east of the
Bahamas. PWat is quite low for this time of year, down under 1.5
inches, and there is little in the way of instability. We`ll show
slight chance PoPs over Georgia along the sea breeze, mainly to
account for slightly better moisture. However, its is certainly
possible that it`ll be rainfree all locations. It`ll certainly be a
noticeable change in the air mass, with max temperatures mainly in
the 80s, and even some dew points down into the 60s with a continued
onshore flow.

Friday: Flat ridging prevails aloft, while at the surface, high
pressure persist overhead, and Tropical Cyclone Ernesto is heading
toward Bermuda. We should be able to get by with yet another
rainfree day, with limited moisture and the lack of forcing. Max
temperatures will be very similar to those on Thursday, with many
places again showing dew points down in the 60s.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
A full latitude trough takes shape across the area over the weekend
into early next week, which not only lifts Ernesto off much further
into the northern Atlantic, but also sends a cold front into closer
proximity from the northwest at some points late in the forecast
period. With warmer temperatures and a return of more typical
moisture, convection will also return. We`ll go slight chance/chance
for now, but given the potential for better shear, these values
might be on the conservative side. temperatures will warm back into
the 90s for all areas away from the beaches.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
KCHS/KJZI/KSAV: A touch of shallow fog/mist will impact the
terminals until 13Z. Otherwise, VFR conditions through early
afternoon.

Scattered convection will develop after 18Z at all three sites
as the interaction of the sea breeze and a weak cold front
occurs in the area. Better chances for convection will occur at
CHS and JZI and tempo groups for TSRA have been included with
the 12Z terminal forecasts from 20Z through 23Z. Any convection
that directly impacts a terminal could produce brief MVFR
conditions and gusty winds.

Coverage of convection diminishes this evening. However, there
are signals that spotty shower activity could continue to impact
CHS and JZI through the night.

Extended Aviation Outlook: Wednesday: Brief flight restrictions
possible at all sites, mainly with afternoon/early evening
convection. The chances for more prolonged flight restrictions might
be at KSAV with a cold front closer by.

Thursday and Friday: Less than 15% chance for convection, with
VFR expected to prevail as deep layer dry air tries to push
southward through the region.

Saturday: Maybe a chance of diurnal convection trying to return.

&&

.MARINE...
Weak surface boundary has already pressed into the SC coastal
waters and will continue to slip southward through the day into
tonight. Winds will (or have) turn north/northeastward behind
the boundary through tonight but largely remain 10 knots or
less. Seas will run 3 feet or less.

Wednesday through Thursday: Fairly decent winds across the marine
area as a cold front sags slowly southward Wednesday and gives way
to high pressure from the north by Thursday. NE winds will reach a
solid 15-20 kt and gusty, and although there could be some gusts
around 25 kt at times, the duration and coverage at this stag e
don`t look to be enough for a Small Craft Advisory.

Friday through saturday: Tropical Cyclone Ernesto will be turning
northward as it reaches our latitude, but is found out close to
Bermuda during this time. Our local gradient steadily slackens as
weak high pressure prevails. That said, some 6 foot seas associated
with the tropical cyclone could make it into the outermost Georgia
waters, and we might require a Small Craft Advisory if this occurs.

Rip Currents: For now we`ll keep a Low Risk of rip currents at the
local beaches Wednesday. However, if winds and/or swells are any
higher than now forecast, the risk might be higher. There is likely
an enhanced risk of rip currents late this week, as swells from
distant Tropical Cyclone Ernesto impact the beaches.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Heat Advisory from noon today to 6 PM EDT this evening for
     GAZ117>119-139>141.
SC...Heat Advisory from noon today to 6 PM EDT this evening for
     SCZ047>049-051.
MARINE...None.

&&

$$