Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington NC
308 PM EDT Monday Aug 31 2015
a trough will persist along the southeast coast into Tuesday.
A middle-level disturbance associated with former Tropical Storm
Erika will move up the southeast coast Tuesday and Tuesday night
and then offshore during Wednesday. Another disturbance will
impact the area Wednesday night and Thursday. High pressure will
build into the area from the north Friday night and through the
Near term /through tonight/...
as of 300 PM Monday...the convection with the deepest moisture
has moved off the coast behind the wave that has shifted to the
north and northeast. A lingering bit of isentropic lift is seen
over land and scattered areas of rain are continuing mainly west
of a Lumberton to Georgetown line this precipitation should end
Model time height sections are showing a drying out of the
atmosphere overnight with the chances of precipitation disappearing
overnight over land. If the cloud cover thins out overnight with the
available low level moisture expect areas of fog to develop mainly
after midnight. Overnight lows continue to range from near 70 well
inland to the middle 70s at the beaches.
Short term /Tuesday through Wednesday night/...
as of 300 PM Monday...progressive pattern through the period. A
trough of low pressure will be aligned right along the coast Tuesday.
A middle-level vorticity maxima associated with former Tropical
Storm Erika will be moving up the southeast coast. This feature
will be approaching the forecast area Tuesday night and is expected to
move off the Carolina coast during the day Wednesday. A ridge building
across the middle of the country near the end of the period will
allow a northwest flow to develop across the Carolinas. A weak shortwave
embedded in the flow is forecast to approach late Wednesday night.
There will be a good amount of dry air moving across the area and
this in and of itself will be good reason to keep the probability of precipitation in
slight chance/chance category. Will show highest probability of precipitation along the
coast ahead of aforementioned middle-level vorticity...late Tuesday
night and Wednesday morning. However...it may end up that most of the
precipitation and certainly the heaviest of the shower and
thunderstorm activity...will be offshore. Will also try to
capture the slight uptick in the potential for convection Wednesday
night with the middle-level shortwave.
Temperatures will return to slightly above seasonable levels for
Long term /Thursday through Monday/...
as of 300 PM Monday...Thursday should be the first full day where the
area is no longer dealing with any remnants of Erika. Precipitable water drops to
about 1.6 inches across much of the area but there will be a middle
level disturbance moving through in northwest flow. GFS now shows a
very weak attendant surface feature and so feel that the low end
scattered (30 pops) that we have in the forecast is just fine. Quantitative precipitation forecast
prospects will be low due to the lower available moisture and weak
forcing. Another middle level feature crosses on Friday but in more of
westerly rather than northwesterly source which may favor better
rain chances due to deeper moisture at least according to European model (ecmwf). GFS
has more of a repeat of Thursday. Large upper ridge builds over the
eastern U.S. And middle-Atlantic over the weekend with its center
well to our north. The same will hold true at the surface. This
will bring a deep easterly flow to the area that often leads to
tropical blue skies laden with towering cumulus and also a few stray
showers mainly along the coast.
Aviation /18z Monday through Saturday/...
as of 18z...most of the heavy rain appears to be coming to an
end. The NAM still is pessimistic...with high probability of precipitation through 00z.
This appears to be overdone and will back off of this scenario.
Tonight...models are in pretty good agreement with introducing
fog after midnight. It has the most dense fog inland...which is
counter intuitive since most of the rain occurred near the coast.
Perhaps better radiational conditions will reside inland and this
is the reason the models are picking up on. Look for possible
LIFR conditions after 08z. Tuesday...becoming VFR an hour or
two after sunrise with light winds.
Extended outlook...predominately VFR with brief morning fog and
isolated/scattered afternoon convection.
near term /through tonight/...
as of 300 PM Monday...winds are still light and variable near the
coast after the low pressure has moved away from the coastal waters.
Winds are beginning to return from the south at 10 to 15 knots at
the buoys to the south and at Frying Pan Shoals. Seas are running at
3 to 4 feet. Overnight...winds will veer to the southwest and then
west at 10 knots. The seas will range between 2 and 4 foot during
Short term /Tuesday through Wednesday night/...
as of 300 PM Monday...a slack pressure gradient is expected to be
in place through the period and this should keep wind speeds to
10 knots or less. SW to S winds during the afternoon and evening both
days should become more offshore overnight and during the morning
due to a land breeze moving offshore. Seas will be mainly 2
feet...but up to 3 feet Tuesday. A weak 8 to 10 second southeast swell will
Long term /Thursday through Saturday/...
as of 300 PM Monday...wind speeds will be capped at just 10 knots
through most of if not the entire period. It may struggle Thursday
and Friday to find an established direction however though north and
east components will tend to be favored. This will be fortified
Friday night into Saturday as a stronger high gets established
across northeastern U.S. Between the lengthening spatial and
temporal fetch on Saturday the wave forecast may rise from 2 to 2-3