301
FXUS62 KCHS 180433
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1233 AM EDT Sun Aug 18 2024

.SYNOPSIS...
A cold front will move through our area Sunday night into
Monday. High pressure will then gradually build in from the
north through the remainder of next week.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
The atmosphere is steadily stabilizing with nocturnal cooling. A
few showers could still occur across the far interior where a
number of convective outflows are working southeast. Slight
chance pops were maintained for a few more hours there. Lows
from the lower 70s well inland to the upper 70s/near 80 at the
beaches and Downtown Charleston are on track.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH TUESDAY/...
Sunday: The mid-levels will consist of a strong trough over the East
Coast. An impulse of energy should round the base of the trough and
move over our area during the evening hours. Further up, a jet
stream initially to our north will become located over our area by
the evening and overnight. At the surface, High pressure will
initially be located off the Southeast Coast. It`s expected to move
further offshore as time progresses. Additionally, a cold front will
be located to the west of the Appalachians at daybreak, it`ll
gradually shift to the east and southeast, becoming located over or
just to the west of our area by daybreak Monday. Flow around the
High and ahead of the front will usher moisture from the Gulf of
Mexico into our area. PWATs should peak in the 2-2.25" range in the
afternoon. The combination of 850 mb temperatures, low-level
thickness values, and compressional heating ahead of the front will
cause high temperatures to be several degrees above normal. They are
forecasted to be in the lower to middle 90s, except cooler at the
beaches. Heat indices should rise close to 108 degrees, mainly along
the coast. But it`s marginal whether we`ll need Heat Advisories. The
combination of the heat and moisture will generate a decent amount
of instability. MLCAPEs should approach the 1,500-2,000 J/kg range
with steepening lapse rates. 0-6 km bulk shear should be in the 20-
35 kt range. Combined with lift from the approaching front,
convection is expected. Models and the long range CAMs disagree on
the exact timing and some of the evolution. But we anticipated
isolated to scattered convection across our area in the afternoon.
Then, a cluster or line of storms originating well to our west and
northwest should move through our area. It should be across our
inland counties late in the afternoon, making its way to the coast
in the evening. Severe storms with damaging winds are the main
concern, so the SPC has our area under a Slight Risk, which seems
reasonable. Heavy rainfall is also a concern given the saturated
grounds. But these storms should be moving fast enough to limit
enormous rainfall amounts. Either way, Flood Advisories cannot be
ruled out. The convection will move offshore later in the evening
and overnight as drier air builds in from the west. Lows will
generally be in the 70s.

Monday and Tuesday: The mid-levels will consist of a strong trough
hovering over the East Coast. The front should be located off our
coast Monday morning. However, it could stall and meander offshore
through Tuesday. Meanwhile, High pressure should gradually build in
from the northwest, with its periphery reaching into our region. The
High should dominate the land forecast, leading to mainly dry
conditions, except for maybe a stray shower along the immediate
coast each afternoon. Highs will only be a couple of degrees cooler
behind the front. Expect them to be in the lower to middle 90s on
Monday and the upper 80s to lower 90s on Tuesday. Lows will be in
the upper 60s to lower 70s.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
High pressure will build in from the north, causing an inland wedge
pattern. Isolated to at most scattered showers and thunderstorms
could develop during the afternoon and evening hours each day.
However, modest subsidence will limit the overall coverage of
convection. High temperatures will gradually lower each day, but
will remain within a few degrees of normal.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
18/06z TAF Discussion:
KCHS/KJZI/KSAV: VFR for much of the period. Scattered
showers/tstms are expected to develop late this afternoon into
this evening for the coastal corridor. Confidence is somewhat
diminished as a number of the near term convective models are
showing a number of possible scenarios for both coverage and
timing for convection. There seems to be a broad consensus that
the periods from roughly 22-02z at KCHS/KJZI and 23-03z at KSAV
will have the best chances for impacts at the various terminals.
For now, the 06z TAFs were trended to use VCTS in the above
mentioned periods. The introduction of TEMPO or prevailing
groups for TSRA may need to be considered in later TAF cycles
as confidence in timing/coverage increases.

Extended Aviation Outlook: A cold front will move through our area
Sunday night into early Monday, bringing brief flight restrictions
due to convection. VFR is expected to prevail beginning later Monday.

&&

.MARINE...
Overnight: Per recent buoy observations and 00z WW3 output, the
start time for the Small Craft Advisory for the Georgia
offshore waters was moved up by several hours as 6 ft seas
should arrive a bit quicker than expected.

Sunday through Thursday: Winds and seas will increase ahead of
an approaching cold front on Sunday. Seas should be around 6 ft
across the GA waters beyond 20 nm, so we have a Small Craft
Advisory in place. The front should move through the waters
early Monday, then stall just to the east of our waters later
Monday. This will cause conditions to improve. By Tuesday, winds
will shift out of the northeast with speeds around 10-15 kt. A
surge of winds is possible on Thursday as the pressure gradient
becomes enhanced due to an inland wedge of High pressure to our
north.

Rip Currents:
Sunday: Long period swell around 12 seconds from distant
Hurricane Ernesto will continue to impact the coast. A High Risk
for rip currents will be in place across all local beaches
through Sunday evening as a result.

Monday: Long period swell around 11 seconds will gradually subside,
but continue to bring impacts to the coast. We have a Moderate Risk
of rip currents for all of our beaches.

&&

.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 from 5 AM early this morning to 9 AM EDT
     Monday for AMZ374.

&&

$$