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FXUS62 KCHS 202206
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
606 PM EDT Wed Sep 20 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.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
Increased pops next 1-2 hours along the Georgia coast per going
radar trends. Expect activity to quickly diminish after sunset.

This Evening and tonight: A pronounced shortwave seen on latest
water vapor imagery will continue to shift over the area this
evening, helping spawn additional showers and/or thunderstorms into
evening hours where greatest sfc heating has occurred and deep
layered moisture characterized by PWATs between 1.7 to 1.9 inches
currently resides. Expect most activity to diminish with the loss of
daytime heating around sunset, but a few showers could linger into
early night hours while the shortwave passes aloft. Weak sfc high
pressure should then persist through much of the night, setting up
somewhat favorable radiational cooling conditions once convective
clouds dissipate and winds go calm. Guidance suggests temps will dip
into the upper 60s inland to lower 70s near closer to the coast
late. These temps along with dewpts remaining in the upper 60s
suggests the potential of fog developing over some locations after
midnight, especially inland where winds go calm and showers and/or
thunderstorms are experienced this evening.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
Thursday through Friday: An upper level trough and an axis of PWATs
1.5 to 1.8 inches will reside over the region and will support
scattered showers/thunderstorms, mainly during the afternoon/evening
hours. Otherwise, above-normal highs in the upper 80s/lower 90s and
lows upper 60s/mid 70s will give way to slightly cooler Friday temps
featuring in the mid/upper 80s and lows mid/upper 60s inland/lower
70s near the coast as high pressure and associated northeast winds
spread into the region.

Saturday: Isolated/scattered showers/thunderstorms should remain
confined to southern/western counties as the upper trough weakens
and surface high pressure pushes drier air into the region from the
north/northeast. Expect high temps in the mid/upper 80s.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
Surface high pressure and rain-free conditions will prevail into
Sunday. Then, the high should weaken and shift inland as Hurricane
Maria passes offshore late this weekend into the middle of next
week. Despite the trend toward cyclonic flow, subsidence between the
high and the western periphery of should maintain mainly rain-
free conditions and a warming trend Sunday through midweek, with
near normal temperatures mainly in the mid 80s Sunday warming
to the upper 80s/lower 90s by midweek.

&&

.AVIATION /22Z WEDNESDAY THROUGH MONDAY/...
Primary concerns:
* None

Could see some shallow ground fog develop at both KCHS and KSAV
prior to daybreak Thursday, but no meaningful impacts are
expected.

Extended Aviation Outlook: Low probability for brief flight
restrictions in early morning fog Friday and Saturday mornings and
in afternoon showers/thunderstorms Thursday, Friday and at KSAV
Saturday. Otherwise, mainly VFR this period.

&&

.MARINE...
This Evening and Tonight: Weak high pressure will prevail over the
coastal waters, resulting in winds/seas that remain well below Small
Craft Advisory levels through tonight. In general, south/southwest
winds will remain at or below 10 kt. Seas will peak no higher than
2-3 ft.

Thursday through Monday: Tranquil conditions featuring light
offshore winds am and onshore winds pm accompanied by 1-3 ft seas
will prevail Thursday. Then, winds will turn northeast and will
increase beginning late this week while a long period swell created
by Hurricane Maria will reach the coastal waters Friday and will
continue into the middle of next week as Maria tracks north and
remains offshore. Small Craft Advisories will eventually be needed
for all waters outside Charleston Harbor beginning late this week
and continuing into the middle of next week. Seas could build to
greater than 10 feet beyond 20 nm this weekend, and hazardous seas
could eventually spread to the coast.

Rip Currents: Astronomical influences and a very minor lingering
swell component will support a moderate rip current risk at
area beaches through this evening. Swell from offshore Hurricane
Maria will create an elevated rip current risk this weekend into
the middle of next week.

&&

.TIDES/COASTAL FLOODING...
A light onshore wind along with astronomical influences will
likely lead to minor coastal flooding along parts of the
Southeast South Carolina coast this evening/early tonight and
potentially along the Southeast Georgia coast. A Coastal Flood
Advisory has therefore been issued for locations along
Charleston County and south to Beaufort County from 7pm to 11
pm. A Coastal Flood Advisory could eventually be needed for
Jasper County, SC and south into Southeast Georgia this
evening/early tonight.

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. Also, the potential
for shallow salt water flooding will persist through early next
week around the times of high tide, particularly along the SC
coast.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...Coastal Flood Advisory until 11 PM EDT this evening for
SCZ048>050.
MARINE...None.

&&

$$
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