Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 251949
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
349 PM EDT Mon Sep 25 2017

.SYNOPSIS...
Hurricane Maria will track northward off the Southeast U.S.
coast through midweek before turning east-northeast and away
from the coast into late week. A cold front will move through
the area early this weekend, followed by high pressure into
early next week.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Tonight: The forecast remains quiet as the region sits between
the circulation of Maria to the east and a weak upper low/trough
along the central Gulf Coast. In this region, an extension of
the ridge that is centered north of Maria will be the primary
feature aloft through the night. The main story will be plenty
of dry air in the mid levels resulting in a notable trough of
lower precipitable water values. As a result, the forecast is
dry. We will continue to see high clouds from Maria`s outflow
stream overhead in the southeasterly flow, while patches of mid
level clouds rotate through around the circulation. The first
half of the overnight period will bring mostly clear skies,
before increasing chances for stratus develop takes over closer
to sunrise. Stratus will primarily be a concern for southeast
South Carolina, especially the Tri-County region. Forecast lows
are in the mid-upper 60s inland and low 70s along the coast.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
Dry weather conditions are expected midweek as high pressure
builds across the region from the north/northwest while
Hurricane Maria shifts northward off the Southeast and Mid
Atlantic coast. The main issue will be a notable warming trend
as a downsloping wind develops across the region Wednesday into
Thursday ahead of a cold front advancing over the Central United
States and toward the Southeast United States. Timing of the
front will play a role in how warm temps peak over the area
Thursday. However, guidance suggests a northwest flow under
mostly sunny skies will support temps warming from the mid/upper
80s Tuesday afternoon to the low/mid 90s by Thursday afternoon,
warmest inland. Overnight lows will range in the upper 60s
inland to low/mid 70s closer to the coast each night.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Chances for showers/thunderstorms will begin increasing late
Thursday into the weekend due to an approaching cold front.
Guidance continues to suggest that the front will complete
passage through the forecast area likely by late Friday or early
Saturday. Cooler high pressure will then begin filling in
behind the front, with early guidance suggesting a high pressure
wedge-type pattern could set up near or over the area Saturday
into Sunday.

&&

.AVIATION /20Z MONDAY THROUGH SATURDAY/...
The main forecast issue for this forecast cycle is the
potential for stratus development late tonight. Model consensus
shows increasing likelihood of at least MVFR ceilings across the
South Carolina zones, including KCHS. Confidence is higher
given that a large area of stratus has persisted much of the day
across eastern North Carolina and the South Carolina counties
north of the Santee River. Introduced MVFR ceilings starting at
10z at KCHS, and once they settle in they should linger through
at least mid morning. There is the potential for ceilings to
lower to IFR, but confidence isn`t high enough in this scenario
yet.

Extended Aviation Outlook: VFR conditions are expected at both
CHS and SAV terminals through late week. However, brief periods
of flight restrictions are possible Wednesday morning and
Thursday morning due to fog.

&&

.MARINE...
Tonight: The local waters will remain on the western periphery
of the circulation of Maria which is centered well offshore. The
pressure gradient will be tightest across the South Carolina
waters, especially off eastern Charleston County where winds
will remain in the 15-20 knot range most of the night.
Elsewhere, 10-15 knots is more likely. Winds will be out of the
north for most of the night, become more north-northwest late.
Seas will remain elevated, 4-7 feet across the nearshore waters
and 6-9 feet in the outer waters.

Tuesday through Friday: Small Craft Advisories will be ongoing
for all coastal waters outside the CHS harbor due to high seas
and long- period swell associated with Hurricane Maria passing
well offshore. Seas could peak as high as 7-9 ft in offshore
Georgia waters and 5-8 ft in nearshore waters, largest in
northern South Carolina waters. A somewhat enhanced gradient
between high pressure building from the north inland and
Hurricane Maria passing to the north offshore will support
northerly winds gradually backing to northwest on Tuesday while
slowly diminishing to 10-15 kt with occasional gusts near 20 kt.
Latest guidance suggests seas will continue to support Small
Craft Advisory criteria for northern South Carolina waters into
early Wednesday and offshore Georgia waters through Wednesday
afternoon or evening, but relatively benign sea conditions are
anticipated Thursday into Friday as winds peak between 5-10
knots and seas remain no higher than 2-4 ft. A cold front
followed by strong high pressure to the north will lead to an
enhanced onshore gradient Saturday, which could lead to a round
of winds/seas supporting another period of Small Craft
Advisories.

Rip Currents: With large and powerful long period swells from
Hurricane Maria to occur, a High Risk for life-threatening rip
currents will persist this evening. NO ONE should enter the surf
due to these extremely dangerous conditions. Conditions will
gradually improve Tuesday, but an elevated risk or rip currents
will persist through at least mid week due to continued long
period swells associated with Maria passing offshore. A Moderate
Risk of rip currents is currently forecast for all beaches on
Tuesday.

&&

.TIDES/COASTAL FLOODING...
Powerful East-Southeast swells originating from Hurricane Maria
passing well offshore along with northeast sfc flow near the
Southeast coast could allow conditions to approach Coastal Flood
Advisory levels with the early afternoon high tide cycle
Tuesday.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...High Risk for Rip Currents until 8 PM EDT this evening for GAZ117-
     119-139-141.
SC...High Risk for Rip Currents until 8 PM EDT this evening for
     SCZ048>051.
MARINE...Small Craft Advisory until 8 PM EDT Tuesday for AMZ352.
     Small Craft Advisory until 6 AM EDT Wednesday for AMZ350.
     Small Craft Advisory until 5 AM EDT Tuesday for AMZ354.
     Small Craft Advisory until 4 PM EDT Wednesday for AMZ374.

&&

$$

NEAR TERM...BSH
SHORT TERM...DPB
LONG TERM...JMC
AVIATION...BSH/DPB
MARINE...BSH/DPB
TIDES/COASTAL FLOODING...


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