Area Forecast Discussion
Issued by NWS Charleston, SC
FXUS62 KCHS 252334
Area Forecast Discussion
National Weather Service Charleston SC
734 PM EDT Sun Sep 25 2016
High pressure will continue to build into the area tonight but
will weaken by late Monday ahead of an approaching cold front. The
front will cross the forecast area and push off the coast by mid
week and high pressure will build into the region by the end of
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
A weak vorticity center located well to the north of the Bahamas
this evening will slowly draw closer to the forecast area
overnight. The feature is already supporting numerous showers with
a few tstms offshore of the Georgia and far southern South
Carolina coasts. This activity will gradually expand closer to the
beaches through the night as surface moisture convergence
increases in response to the formation of a weak coastal trough
off along the Georgia coast. Expect the greatest coverage of
showers to occur between Tybee Island and Folly Beach where
surface moisture convergence should be the most intense along the
head of the coastal trough. Increased pops to 40-50% in this
corridor with the early evening update, but further adjustments
may be needed later as trends become more apparent.
.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
Mid level heights will fall in response to a closed low and potent
shortwave energy digging into the Upper Midwest and Great Lakes. At
the surface, high pressure centered over the northeastern U.S.
early Monday will gradually shift offshore as a cold front
approaches from the west. This will place the forecast area solidly
in the warm sector through much of the period. Elevated moisture and
proximity to a coastal trough will keep precipitation chances in the
forecast each day. Decent instability will support mention of
thunder, however severe threat will remain low.
Temperatures are forecast to be a few degrees above late September
climo, with highs in the mid/upper 80s and lows in the upper 60s/low
.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
The cold front will move through the area Wednesday night, with
global models showing the front over the coastal waters by sunrise
Thursday morning. However, given the uncertainty in terms of the
weakening parent low near the Great Lakes, the front may drag its
feet getting through the area, moving over the waters and stalling
out well to our south and west by midday Thursday. Either way,
strong, dry continental high pressure will fill in behind the front
and quiet weather will ensure for the second half of the week. Temps
will be near to a few degrees below normal through the period.
.AVIATION /00Z MONDAY THROUGH FRIDAY/...
Mostly VFR. Could still see a period of MVFR cigs at KCHS prior
to sunrise, but much will depend on how convection offshore
evolves. Latest guidance has certainly backed off on the Models
are all over the place with the depiction of showers Tuesday, so
will not include a mention attm until trends become a bit more
apparent and confidence increases.
Extended Aviation Outlook: Flight restrictions will be possible in
showers and thunderstorms through Wednesday.
Tonight: High pressure will continue to build inland and as
coastal trough will develop and sharpen through the night. As this
occurs, a tightening northeast gradient will result in
strengthening flow, especially along the South Carolina coast. The
forecast features 15-20 knots for the Charleston County coast with
lesser winds elsewhere. The setup favors another round of showers
and isolated thunderstorms developing tonight, and the highest
rain chances are across the coastal waters. Seas will range 2-4
feet through the night.
Monday through Friday...marine conditions will be fairly quiet
through the work week. A coastal trough will develop Monday and
persist through Tuesday before a cold front approaches from the
west. The front is expected to move offshore mid-week with high
pressure to return late week. Wind speeds on average will be at or
below 15 knots, with seas 2-3 feet.