Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 221142
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
742 AM EDT Fri Sep 22 2017

.SYNOPSIS...
High pressure will prevail through this weekend. The high will
weaken and shift inland as Hurricane Maria tracks northward off
the Southeast U.S. coast through the first half of next week. A
cold front could approach the forecast area late next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Today: Surface high pressure will remain to the north while
weak synoptic flow remains onshore. In the mid levels, weak
troughing exists in a positively tilted fashion with a stagnant
lobe of vorticity at 500 MB extending across the forecast area.
There is a little pocket of -10C at 500 MB noted across the
forecast region this afternoon. Morning sunshine will give way
to cumulus/stratocu this afternoon with some high clouds mixed
in as well. In terms of convection, instability progs look just
a bit weaker than Thursday. Isolated showers and thunderstorms
are expected this afternoon. Some drier air aloft seen on
soundings however DCAPE values appear lower than yesterday and
risk of isolated strong storms appears really low-end. Highs
will not be as warm today many areas with upper 80s most common.

Tonight: Isolated early evening convection is possible well
inland but mainly prior to sunset. Skies will be clear to
partly cloudy with lows in the mid to upper 60s. Patchy fog is
possible once again, especially inland from the U.S. 17
corridor.

&&

.SHORT TERM /SATURDAY THROUGH MONDAY/...
Dry high pressure will settle over the forecast area. On Saturday,
relatively higher ambient moisture will support a slight chance for
shower/thunderstorm activity mainly across Georgia zones, with South
Carolina zones appearing mostly dry based on the latest guidance.
Sunday and Monday appear too dry to support mentionable precipitation
over land zones in the forecast. Above normal temperatures are
expected, with highs in the mid to upper 80s and lows in the mid
to upper 60s, around 70 at the beaches.

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
Inland high pressure will persist through early next week while
Hurricane Maria is forecast to remain offshore of the Southeast U.S.
coast as it tracks north through the middle of next week. While some
showers could skirt coastal areas early next week as Maria passes
by, persistent, weak NVA under high pressure should help
mitigate precipitation chances. For much of the week, mainly dry
conditions are anticipated with temperatures likely remaining
above normal.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
Shallow ground fog and thin stratus layers around sunrise,
initialized in the 12Z TAFs. MVFR at KSAV with light fog and
patchy stratus, small potential for brief IFR cigs there as
well. VFR today with slightly lower chances for spotty
convection this afternoon. Patchy fog is possible at both
terminals again late tonight.

Extended Aviation Outlook: Mainly VFR conditions expected. Low
probability for brief flight restrictions in early morning fog
and/or low clouds Saturday morning at either terminal. Low
probability for brief restrictions due to isolated shower and
thunderstorm Saturday afternoon/evening, primarily affecting
KSAV.

&&

.MARINE...
High pressure from the Ohio Valley to the Mid Atlantic region
will be our dominate synoptic feature through tonight. Gradients
will not be tight and wind speeds will continue to be less than
15 knots. We will begin to see building swells from Hurricane
Maria but suspect the initial wave guidance may be a bit too quick
given recent episodes of arriving swells with prior tropical
cyclones this year. Overall, we made just small timing adjustments
based on recent trends and maintained the SCA timing for hazardous
seas over our 20-60 NM GA waters that initiates at mid afternoon
today. Seas should build to 4-5 feet across near shore waters
by late tonight.

Saturday through Tuesday: Seas 6 ft and building are expected to
push into nearshore waters by early Saturday morning due to swell
from offshore Hurricane Maria. A prolonged period of Small Craft
Advisories is expected. Generally NE winds 10-15 knots with some
gusts to 20 knots are anticipated through early next week.

Rip Currents: Swell from offshore Hurricane Maria will slowly build
at the beaches. This results in a moderate risk of rip currents
today and will we likely maintain moderate to high risks through
early to mid next week.

&&

.TIDES/COASTAL FLOODING...
Powerful surf created by offshore Hurricane Maria will drive
significant wave run-up, which could cause further beach erosion
this weekend into early next week. High Surf Advisories may be
required. Also, the potential for shallow salt water flooding
will persist through early next week around the times of high
tide, particularly along the South Carolina coast.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Small Craft Advisory for hazardous seas from 2 PM this
     afternoon to 6 AM EDT Wednesday for AMZ374.

&&

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



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