Area Forecast Discussion
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FXUS62 KILM 231056
Area Forecast Discussion
National Weather Service Wilmington NC
656 AM 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/...
As of 700 AM Friday...Low pressure aloft has opened up since Thu,
but general troffiness will linger across the area through the
period. Low pressure at the surface still appears stuck across
Williamsburg and Georgetown counties this morning. Weak surface
low should continue to be nudged ENE through Saturday morning.
This will mean another day of unsettled weather with the potential
for significant rainfall given the abnormally high precipitable
water values. These values will be dropping below 2 inches inland,
but remaining near or just above 2 inches along the coast through
the day. We are watching another plume of tropical moisture
working its way northward along the southeast coast. This deep
moisture could again enhance rainfall rates across mainly our
coastal areas. We will continue to access whether a Flash Flood
Watch is warranted for a small portion of the area later today.
Will carry scattered to numerous showers and some thunderstorms with
heavy rain. Coastal areas should again see the heaviest rainfall
amounts. Generally we are expecting one quarter to three quarters of
an inch of rain. However, these amounts could be easily quadrupled
in areas where convection repeatedly redevelops with the risk for
excessive rainfall, given the antecedent conditions, highest along
the more immediate coast
POPs will be trending down, lastly along the coast by/during the
eve as drier air begins to seep into the area.
.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 TUESDAY/...
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
NEAR TERM /THROUGH TONIGHT/...
As of 700 AM Friday...Weak low pressure will remain in the area
and this will keep wind speeds under 10 kt through the period. The
wind direction will vary depending on the position of low
pressure. The wind direction tonight will be mainly from the N.
Seas will be 2 to 3 ft, but near 4 ft out around Frying pan Shoals
due to the 11 to 12 second easterly swell generated ahead of
distant Tropical Storm Karl.
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.