Area Forecast Discussion
Issued by NWS Wilmington, NC-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS62 KILM 231628
Area Forecast Discussion
National Weather Service Wilmington NC
1228 PM EDT Fri Sep 23 2016
Weak low pressure will circulate near the South Carolina coast
today. The low will drift offshore Saturday and allow high
pressure and drier air to build in. A modest cold front will drop
south across the area Sunday, followed by high pressure through
Monday. Rain chances will increase by midweek ahead of another
.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --As of 1230 PM Friday...Surface low pressure is located on
satellite and surface observations just west of Georgetown, SC.
This swirl has been one of the most persistent weather features
we`ve had in ages! Models suggest this low should slide southward
tonight, eventually allowing some drier air to punch in from the
north. A trough axis just off the coast separates east and
southeast winds observed offshore from the more northeasterly
winds nearshore and inland.
Light showers inland have been decreasing most of the morning.
Showers developing along the trough offshore are the most
impressive ones currently. Models suggest daytime heating should
be sufficient to fire new convection today given surface-based
CAPE of 500-1000 J/kg and a moist, uncapped atmosphere. Very slow
cell motion is indicated today, only 3-7 knots in most cases.
Locally heavy rainfall is possible, especially across coastal SE
North Carolina where the best low-level convergence may develop
due to more insolation from breaks in the cloud cover. Given how
much rain fell yesterday across coastal New Hanover and Pender
counties, we`ve issued a short-term Flash Flood Watch for this
area, mainly because soils are saturated due to the 5-8 inches of
rain that fell yesterday near and east of Highway 17. It might
only take 1-2 inches to create flash flooding today.
No significant changes have been made to forecast high temps
today: 81 to 84 for most areas. I have bumped up evening PoPs
along the coast as models suggest showers and storms may linger
past sunset before the drier air begins to bleed in from the north
-- End Changed Discussion --
.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
As of 300 AM Friday...Some of the drier air seen on water vapor
imagery should be able to work its way into the area by Sat.
However, there still will be some troffiness across the area. A
backdoor cold front will approach from the N Sat night and should
move across the forecast area during Sun. Will keep POPs largely
below threshold on Sat with a small POP across southern areas where
moisture will be slightly greater. Then will include a small POP for
Sun with the front moving across the area. Precipitable water values
will be dropping through the period resulting in much lower rainfall
rates and we are not expecting significant rainfall during the
More sunshine on Sat should bring highs to the mid and upper 80s.
Highs on Sun will still be above normal, lower to mid 80s.
Lows will be in the upper 60s to lower 70s Sat night and mid and
upper 60s Sun night with near 70 at the beaches.
.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 300 AM Friday...A mid and upper level ridge axis will
transition over the area Monday, ahead of a deep upper low that
will be dropping across the Great Lakes. Surface high pressure
build in from the north on Monday but shift offshore Tuesday. This
will result in an increase of moisture off the Atlantic as winds
become southeast, and expect rain chances to increase Tuesday and
Wednesday ahead of a cold front which is expected to move off the
coast by early Thursday.
.AVIATION /12Z FRIDAY THROUGH WEDNESDAY/...
As of 12Z...A surface low is S of KMYR with a weak trough along the
Flight conditions will be a general repeat of the previous 24 hours.
There is high confidence LIFR will lift to 14-15Z, after which MVFR
will occur most of the morning. Cigs will improve to VFR by this
afternoon outside of precipitation. Precipitation is currently curring
in widely scattered bands rotating slowly around low pressure to the
south. Satellite picture suggest enhanced clouds not as prevalent as
yesterday morning so this mornings precipitation may be less. Convection
will increase as the afternoon approaches along the coast and in bands
rotating around the low. Confidence is low as to where exactly bands of
precipitation will set up. If a band sets up directly over a terminal
there could be an extended period of SHRA/IFR/VCTS. Due to low confidence
of timing this is not indicated in TAFs. Have included TEMPO groups
indicating MVFR and will amd as precipiation develops as necessary for IFR.
Models suggest the surface low will fill and weak high pressure will build
into the terminals overnight. With moist low levels, light winds and sct
skies there is increasing confidence of dense fog development.
EXTENDED OUTLOOK...MVFR/IFR stratus/fog possible late Friday night
and Saturday morning. Expect mainly VFR Sunday and Monday, but
chances for showers and tstms will begin to increase Tuesday and
-- Changed Discussion --NEAR TERM /THROUGH TONIGHT/...
As of 1230 PM Friday...Satellite data and surface observations
show the weak low pressure area centered just west of Georgetown,
SC. A trough axis extending along the coast of the Carolina
separates east or even southeast winds offshore from northeast winds
at the beaches. The low should weaken further and sink southward
later today, with mainly northeasterly wind persisting across the
0-20 nm coastal waters.
Scattered showers and t-storms may diminish in coverage near Cape
Fear as the main focus for storms shifts inland. Perhaps of equal
importance, the atmosphere is favorable for waterspout development
Seas are currently 2-3 feet. Long-period swells from growing
Tropical Storm Karl just south of Bermuda, already showing up in
spectral wave data from Frying Pan Shoals, will increase this
afternoon and tonight. Combined seas could reach 4 feet in some of
the outer portion of the coastal waters, mainly near and north of
Cape Fear, tonight.
SHORT TERM /Saturday FRIDAY THROUGH SATURDAY NIGHT/...
As of 300 AM Friday...Weak surface low pressure should move further
offshore. A backdoor cold front will move across the waters on Sun.
The strongest wind speeds this period will be in the wake of the
front, Sun and Sun night. Winds speeds will be up to 15 to 20 kt,
otherwise sustained winds will be 10 to 15 kt. The wind direction
will be mainly NE, becoming ENE Sun night. Seas will build to 4 to 5
ft Sun and Sun night as a robust easterly swell remains.
LONG TERM /MONDAY THROUGH TUESDAY/...
As of 300 AM Friday...The period will begin with northeast flow
as high pressure ridges in behind Sundays cold frontal passage. As
the high transitions off the mid-Atlantic coast Monday afternoon,
winds will veer to the east, then south behind an inverted trough
that will lift north across the waters Tuesday. Onshore flow and a
moderate pressure gradient will support 15 knots of wind and 3-4 ft
seas on Monday, and the continued onshore trajectory Tuesday
should see seas build to 4 ft throughout, with perhaps some 5
footers in the vicinity of Frying Pan Shoals, and near 20 nm out.
-- End Changed Discussion --
NC...Flash Flood Watch until 9 PM EDT this evening for NCZ105>108.