570
FXUS62 KCHS 172041
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
441 PM EDT Sat Aug 17 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 SUNDAY MORNING/...
Water vapor images indicated that the leading edge of a H5 long wave
trough was sweeping across the western Carolinas and northern Georgia
this afternoon. Rounds of showers and thunderstorms may develop
ahead of the trough tonight. The first round of convection should
continue to drift over the inland counties of the forecast area this
afternoon. This activity should dissipate around sunset this
evening. High resolution guidance indicates that clusters of
thunderstorms will develop ahead of the trough across the I-85
corridor of GA and SC this evening. Given a wide field of weak DCAPE
across the area tonight. A weakening, second round, of convection
and associated outflow boundaries may arrive over the forecast area
late tonight. Coverage should remain limited to isolated over
portions of the SC Lowcountry. Low temperatures are forecast to
range from the low to mid 70s.

&&

.SHORT TERM /6 AM SUNDAY 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 /21Z SATURDAY THROUGH THURSDAY/...
KCHS/KJZI/KSAV: VFR conditions expected through 18Z Sunday.

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...
Tonight, the sfc pattern will support southwest winds between 10 to
15 kts across the marine zones. Seas should remain between 3 to 4 ft
through most of tonight. Portions of the outer GA waters may see
some 5 ft seas late tonight.

Extended Marine: 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:
Today: The rip current risk remains in the high category for
today as long periods swells from Hurricane Ernesto will
persist. The rip currents will be especially strong at times
given the power values noted on spectral plots from both the
Edisto (41004) and Grays Reef buoys (41008).

Sunday: Long period swell around 12 seconds from distant
Hurricane Ernesto will continue to impact the coast. We have a
High Risk of rip currents for all of our beaches.

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 Sunday evening for GAZ117-119-
     139-141.
SC...High Risk for Rip Currents through Sunday evening for SCZ048>051.
MARINE...Small Craft Advisory from 8 AM Sunday to 9 AM EDT Monday for
     AMZ374.

&&

$$

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