Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 240121
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
921 PM EDT Wed Aug 23 2017

.SYNOPSIS...
A cold front will move into the area tonight and linger nearby
through the end of the week. A wave of low pressure could form
along the front offshore Friday, as high pressure builds from
the north through the weekend.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
Showers/tstms continue to percolate from the South Carolina
Midlands into the Pee Dee ahead of an approaching cold front.
The front is on target to approach the interior South Carolina
zones by daybreak Thursday keeping the entire forecast area in
the warm sector. Guidance has been consistent in keeping the
bulk of the frontal convection north of the Santee River with
only some activity brushing/developing the region north of the
I-26 corridor. Opted to pull back pops even more with this
update; dropping mentionable pop across Southeast Georgia and
far southern South Carolina with 20-40% pops confined to the
region roughly along/northeast of an Allendale-Hilton Head line.


&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
A weak cold front will very slowly migrate southeast through
the area Thursday through Saturday. On Thursday we expect the
day to begin with scattered showers and tstms moving offshore
with a shortwave, followed by a relative lull until the
afternoon when another shortwave moves in from the west. A
moderate sea breeze will also develop and provide a focus for
convection.

Drier, cooler high pressure will steadily build from the north
Thursday night through Saturday while a relatively zonal flow
develops aloft. The greatest chance for showers and tstms will
shift to coastal SC and southeast GA along and south of the
advancing front. High temps will be down to the mid/upper 80s by
Saturday.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
Surface high pressure will continue to reach into the area from
Canada. Fairly reasonable model agreement depicts a coastal low
developing off the GA/SC coast by late this weekend. In addition,
guidance suggests that the remnants of Harvey will track towards the
forecast area from south Texas. At least some degree of wedging of
the high pressure over the Carolinas seems probable with low
pressure to the east and west, resulting in a cloudy and potentially
unsettled period. Daytime warming would be tempered in this regime,
with highs averaging in the mid-80s appearing reasonable at this
time. By Tuesday, deeper moisture may provide greater coverage of
convection, but model solutions diverge considerably by this time,
increasing forecast uncertainty.

&&

.AVIATION /01Z THURSDAY THROUGH MONDAY/...
Primary concerns:
* Thunderstorms around KSAV

Thunderstorms will linger around KSAV until right around 00z TAF
issuance time. May carry a TEMPO or VCTS depending on radar
trends at 2330z. Shower/tstms could approach KCHS prior to
daybreak as a cold front draws closer, but latest guidance keeps
activity well to the north. Will not include any mention with
the 00z TAFs. Otherwise, VFR. Risk for showers/tstms will linger
into Thursday, but impact probabilities remain too low to
justify a mention at either terminal.

Extended Aviation Outlook: Brief flight restrictions will be
possible in mainly daytime showers/tstms Thursday through
Saturday. Greater potential at KSAV.

&&

.MARINE...
Tonight: Southerly winds will shift southwest as a cold front
approaches. The gradient will continue to tighten through this
evening and winds will peak between 15 and 20 knots for a
period into the early morning, unless any convection or
convective boundaries moving offshore disrupt the synoptic wind
flow. Winds will gradually diminish late tonight as the cold
front nears from the NW and N. Seas will mainly range from 2 to
4 ft, highest near the Gulf Stream.

Thursday through Sunday: Southwest winds less than 15 kt will
continue through Thursday night before shifting to northeast on
Friday as a cold front slowly drops into the area. A fairly
tight pinched northeast gradient is expected to develop Saturday
and persist through at least Monday as a wave of low pressure
develops along the stalled front while high pressure builds from
the northwest. Small Craft Advisories are likely for most if
not all waters starting at some point Saturday. The low pressure
system is currently forecast to make its closest approach next
Monday into Tuesday, potentially as a tropical cyclone.

Rip Currents: A 2-3 ft swell every 9-10 seconds along with
moderately strong onshore winds will keep an elevated risk of
rip currents along the Charleston County coast into this evening.

&&

.EQUIPMENT...
The temperature and dew point sensors at the Downtown
Charleston observation site (KCXM) could periodically fail.
Parts are on order and technicians will attempt to resolve the
problem once they arrive.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.

&&

$$



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