375
FXUS62 KCHS 090754
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
354 AM EDT Tue Jul 9 2024

.SYNOPSIS...
A surface trough will remain over inland areas this week while
high pressure persists over the western Atlantic.

&&

.NEAR TERM /THROUGH TONIGHT/...
Overview: Showers and thunderstorms persist this morning just
off of the Charleston county coastline. This is due to a weak
north/ south surface trough intersecting the SC coastline near
Charleston county and extending offshore to the south and
towards Georgetown county to the north. In the mid-levels of the
atmosphere, a weak high pressure exists across the southeastern
United States with a pesky low pressure retrograding southwest
between Bermuda and Miami, FL. During the day today, the mid-
level low will get sheared apart and pulled southwest underneath
the upper-level ridge axis. As this occurs, fragments of
vorticity will also advect southwest across coastal SC and GA.
The surface trough mentioned above will respond to this through
the day by slowly translating to the southwest.

Temperatures: As the mid-level low gets sheared apart
underneath the upper-level high pressure, a slight strengthening
of the ridge is forecast. Latest forecast for 1000/ 850 mb
thicknesses have risen to around 1425/ 1430 m across the coastal
counties and 1430/ 1435 m towards inland GA/ SC. Given the
placement of the upper-level ridge this makes sense. Compared to
Monday, these thicknesses are similar for coastal counties and
slightly higher for inland counties. This will make high
temperatures in the low to mid 90s across the area today, or a
degree or two warmer compared to Monday (except along the
coast). This combined with a surge of slightly higher dewpoints
off of the Atlantic (ahead of the surface trough) equates to
heat index values up to 109 degrees this afternoon. A heat
advisory is in effect today from 11 AM to 8 PM. Tonight, expect
low temperatures in the mid to upper 70s with winds quickly
falling off as the PBL decouples.

Precipitation: The other main question today is the coverage of
potential showers and thunderstorms. High res guidance has been
all over the place the last several days for each afternoon,
and today is no different. Several key differences exist today
though compared to the last several days. Mid-level dry air that
had been in place near the Tri-County is now gone with PWATs
across the region around 2.50". This very moist air mass even by
summer standards (near max recorded values) is forecast to stay
in place across the region today. Also, there is weak mid-level
PVA sliding southwest underneath the mid-level ridge across
coastal SC and GA. A weak surface trough reflection has already
formed in response and is forecast to translate southwest with
the PVA this afternoon. MLCAPE values are also forecast to max
out around 1500/ 2000 J/kg. Given the above, have kept likely
PoPs in the forecast but started with the highest PoPs near
Charleston and then slowly translate higher PoPs southwest in
association with the surface trough. Rainfall totals of 1 - 2"
are the most likely with isolated totals greater than 3".

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
The mid-level ridge across the western Atlantic will continue to
extend west into the local forecast area on Wednesday. Weak
upper vort maxima may rotate through the area, particularly
across southeast GA during the afternoon. The sea breeze should
spur scattered showers and thunderstorms during the day, with
the greatest coverage potentially drifting inland during the
afternoon. High temps expected to reach 91-94 degrees while
dewpoints remain in the upper 70s. The current forecast shows an
area of peak heat indices of 108-111 across southern SC, so we
may need another Heat Advisory on Wednesday.

A weak cold front is expected to push into the area from the
west on Thursday, spreading some drier air across southeast GA.
The best moisture and convergence is expected to be across
southern SC where we show the highest PoPs.

Friday will feature an increase in upper shortwave energy. A
weak surface low is forecast to develop across southeast GA,
with the greatest moisture and forcing over southern SC. Fairly
good coverage of showers and thunderstorms is anticipated,
especially in SC.


&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
A mid-level ridge will gradually build over the eastern United
States Saturday through Tuesday. A relatively typical summertime
coverage of diurnal showers and thunderstorms expected.
Temperatures will steadily increase during the period, with
highs in the upper 90s by early next week.

&&

.AVIATION /08Z TUESDAY THROUGH SATURDAY/...
KCHS/KJZI/KSAV: Convection is still ongoing near the Charleston
coast early this morning thanks to a weakness aloft which is
slowly heading southwest. Showers and thunderstorms will likely
continue to propagate slowly to the southeast, or off the South
Carolina coast as the overnight land breeze takes over. During
the day Tuesday, another round of showers and thunderstorms
appear possible with the greatest chance of precipitation again
being towards KSAV (which is in the path of the weak forcing).
However, all terminals will include a mention of thunder given
the widespread instability available. Mostly VFR conditions are
forecast through the period.

Extended Aviation Outlook: Scattered afternoon showers and
thunderstorms may produce brief flight restrictions.

&&

.MARINE...
Showers and thunderstorms persist off of the Charleston county
coastline this morning along a weak surface trough. Winds west
of the trough are southwest with winds ahead of the trough being
out of the south/ southeast. Through the day today, the surface
trough will pull west with winds slowly backing from the south
around 10 kt. Seas 2 to 3 ft. Showers and thunderstorms will
also be possible near the surface trough.

Wednesday through Sunday: Southerly flow will persist through
the period. Conditions will remain below advisory criteria with
wind speeds largely in the 10-15 knot range and seas 2-3 feet.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Heat Advisory from 11 AM this morning to 8 PM EDT this evening
     for GAZ087-088-099>101-114>119-137>141.
SC...Heat Advisory from 11 AM this morning to 8 PM EDT this evening
     for SCZ040-042>045-047>052.
MARINE...None.

&&

$$

NEAR TERM...Haines
SHORT TERM...JRL
LONG TERM...JRL
AVIATION...Haines/JRL
MARINE...Haines/JRL