073
FXUS62 KCHS 162042
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
442 PM EDT Fri Aug 16 2024

.SYNOPSIS...
High pressure will remain over the area through most of this
weekend. A cold front will push across the area Sunday night,
then remain nearby through late week.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
A mid and upper trough will dig through the Great Lakes region,
while an extensive mid and upper ridge stretches across the southern
states and into the local region. High pressure at the surface will
remain atop the area, while Hurricane Ernesto impacts Bermuda as it
passes around 900 miles from the immediate region. A dry and stable
air mass will encompass our counties, so we continue with the
rainfree conditions, allowing us to dry out further. Earlier we were
able to drop the Flood Advisory for Dorchester County near and along
the Ashley River, but we still have some flooding in the Richmond
Hill area near the Ogeechee River.

Diurnal cumulus will dissipate this evening, and while there might
be a few mid or high level clouds drifting through at times, skies
will be mainly clear. Light or calm winds and the dry air mass will
allow for another night with most temperatures below climo. But with
a southerly boundary flow to develop and slight modification of the
air mass, lows will be a bit warmer than the last two nights.
Generally upper 60s and lower 70s inland from the barrier islands,
with mid and upper 70s closer to the ocean.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
Saturday: H5 ridge will build across the deep south, with a subtle
ridge across the forecast area. At the sfc, weak high pressure will
remain across the western Atlantic as a broad trough remains across
the Foothills of the Carolinas. This pattern will support light
south-southwest across the forecast area. However, as temperatures
warm into the low to mid 90s, a weak sea breeze should develop
Saturday afternoon and evening. Forecast sounding across the sea
breeze indicate that the environment will remain weakly capped.
Guidance does support some convection sourced from inland GA
reaching inland SE GA during the afternoon, highlighted with SCHC
PoPs. Saturday night, guidance indicates that a vort max will
accompany the approaching H5 trough. The forecast will highlight
SCHC across portions of the SC Lowcountry late Saturday night into
Sunday.

Sunday: A cold front will slowly approach from the west through the
day. Sfc winds are forecast to shift from the southwest, keeping the
sea breeze along the coast through early afternoon. The sea breeze
is expected to drift inland during the mid to late afternoon,
resulting in dewpoints to climb into the mid to upper 70s. Scattered
showers and thunderstorms are forecast to develop between the sea
breeze and the approaching cold front. High temperatures are
forecast to range in the low to mid 90s. Heat index values will peak
near 108 across portions of the GA coast and the southern SC coast.

Interesting setup across the region Sunday evening. Models indicate
that an MCS will develop across the western Carolinas Sunday
afternoon, then tracking east. The MCS is expected to reach the
forecast area Sunday evening, pushing over the Atlantic Sunday
night. Forecast soundings show CAPE values ranging from 1500-2000
J/kg, with modest values of DCAPE. Hodographs indicate a deep curved
profile, with 0-6 km bulk shear around 30 kts and 0-3 km helicity
around 300 m2/s2. This environment should support a few organized
storm clusters, producing swaths of strong to severe wind gusts. In
addition, it is possible, that a few supercells may develop ahead of
the MCS. SPC has highlighted most of the interior counties with a
Slight risk for severe thunderstorms.

The region will remain under the H5 trough axis on Monday. Isolated
to scattered showers and thunderstorms may develop across the
coastal counties during the afternoon. High temperatures are
forecast to range in the low to mid 90s.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Aloft, an upper-level trough extending from extreme eastern Canada
down to Florida Keys will stall nearby into mid-week before finally
being pushed offshore over the weekend. By Monday night, this
pattern should feature a building high pressure to the north as the
cold front from the associated trough becomes stationary offshore.
This set-up should allow for cold air damming, or CAD, to take
place over the region allowing for cooler temperatures and drier
conditions Monday through Thursday. However heading into
Friday, due to some isentropic lifting, chances for some
isolated to scattered showers become likely.

&&

.AVIATION /21Z FRIDAY THROUGH WEDNESDAY/...
VFR conditions are expected to prevail at the KCHS/KJZI/KSAV
terminals through 18Z Saturday.

Extended Aviation Outlook: A cold front is forecast to impact the
region late this weekend/early next week, bringing the risk of brief
flight restrictions within showers and thunderstorms.

&&

.MARINE...
This evening and tonight: Hurricane Ernesto will pass by Bermuda,
while high pressure sits right overhead of the local waters. This
will result in winds veering around to the SE and S through the
night, with speeds mainly 10 kt or less. Guidance continues to be
overdone on seas by about a foot, and as a result we have adjusted
the forecast accordingly. We now show some 6 footers making it into
the nearshore South Carolina waters between 8 pm and 4 am,
continuing to back off on the start time of the Small Craft
Advisory, valid during that time. Even that might continue to
be a little overdone. On the Georgia waters, seas will remain 5
ft or less on the nearshore waters, so no advisory there. But
the outer waters will experience 6 or 7 footers, so we continue
the advisory on the waters 20-60 nm offshore.

Saturday through Wednesday: Seas should decrease to 3-5 ft with
light and variable winds early Saturday with high pressure in place.
Saturday night into Sunday winds and seas will gradually increase
ahead of an approaching cold front that is expected to push across
the local waters Monday. Winds could surge from the SW to around 20
kts with gusts 20-25 kt Sunday night. In addition, seas could build
up to 6ft across portions of the outer GA waters Sunday. Conditions
will improve throughout the day Monday with seas dropping to 2-3 ft,
and winds shifting northeast 10-15 kt for Tuesday and Wednesday.

High Surf: Local guidance has been running about a foot or so larger
than webcams would show, which has generally been 3 or 4 foot
breakers at the coast. As a result we continue to refrain from
issuing a High Surf Advisory, but we will continue to monitor.

Rip Currents: So far we have received 7 reports of rip currents at
Tybee Beach today.

Since long period swell (13 to 15 seconds) from Hurricane will
continue to impact the beaches through the weekend, we have a High
Risk of Rip Currents at all beaches through Sunday.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...High Risk for Rip Currents through Saturday evening for GAZ117-119-
     139-141.
SC...High Risk for Rip Currents through Saturday evening for SCZ048>051.
MARINE...Small Craft Advisory from 8 PM this evening to 4 AM EDT
     Saturday for AMZ350-352.
     Small Craft Advisory until 8 AM EDT Saturday for AMZ374.

&&

$$

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