Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington NC
1024 am EDT Sat Aug 1 2015
a weak front will wave across the coastal Carolinas this
weekend...producing scattered showers and thunderstorms near the
coast. The front should dissipate Sunday night. Bermuda high
pressure well offshore will build westward next week. Temperatures
will remain seasonable to slightly above through the weekend and
during all of next week.
Near term /through tonight/...
as of 1030 am Saturday...with the morning update I have adjusted
cloud cover somewhat to represent the overcast shield hovering
just along the coast. Showers and thunderstorms are associated
with this feature due to good difluence aloft. High resolution
guidance and the latest NAM are still advertising scattered to
isolated coverage of convection this afternoon mainly along the
coast and arching southwest into Williamsburg County. No changes
to the probability of precipitation or temperature forecast.
Short term /Sunday through Monday night/...
as of 300 am Saturday...stubborn stationary front will remain in the
vicinity Sunday before finally dissipating on Monday. This will
continue at least low-chance of showers/thunderstorms southeast of the front
Sunday...but Monday is looking increasingly dry. This front is
stalled beneath a broad longwave trough which has enveloped much of
the eastern half of the Continental U.S....but is Pretty Flat locally and thus
is unable to advect it offshore. However...by Monday the ridge
across Texas begins to bulge NE and it is this development which
will cause the front to finally dissipate.
Not expecting widespread convection Sunday...and the inherited schc
along the coast only will remain where precipitable waters are forecast to rise to
1.25 to 1.5 inches. Towards I-95...a very sharp precipitable water gradient will
exist with much drier air across that area...and thus no pop is
forecast. Any convection will wane diurnally Sunday night as no
significant upper forcing is expected. As the front washes out on
Monday...guidance is surprisingly aggressive with precipitation across the
eastern half of the County Warning Area. Only reason for this must be a vorticity maximum
prognosticated to swing just north of the area Monday afternoon...but with
soundings showing very dry air in place still believe this is
overdone. Will drop pop to schc from the inherited low-chance for
Monday...with again the coastal third of the County Warning Area most favored.
Temperatures this period will be slightly above climatology norms for
highs...around 90 at the coast and as warm as 95 well inland. Lows
will be a bit above normal 72-76 both nights...warmest at the
Long term /Tuesday through Friday/...
as of 300 am Saturday...broad trough across the east will transition
to flat ridging from the arklatex through mid-week. This creates
drier and warmer weather Tue/Wed...although the GFS looks too warm
with its extreme heat and will favor the cooler MOS numbers. The
very dry forecast soundings combined with the upper ridging will
prevent much in the way of convection the first half of the period
though. Thursday will be a transition day as troughing begins to re-
amplify across the east...led by a cold front dropping through the
Ohio Valley. This front will slowly traverse the middle-Atlantic Friday and
into our area at the end of the period. This will bring slowly
cooling temperatures and increasing rain chances Thu/Fri...with much
cooler temperatures possible just beyond the extended.
Aviation /14z Saturday through Wednesday/...
as of 12z...a stationary front marked by significantly lower dew
points was located near a kflo/klbt line. It was VFR with clear
skies at kflo/klbt early this morning...while coastal terminals
had VFR ceilings/patchy MVFR visibilities. Showers and thunderstorms are
currently located just offshore and moving away from the coast.
Winds are light and variable at all terminals.
Any MVFR visibilities should improve to VFR by 13z. High resolution forecasts
suggest precipitation will remain offshore through the morning with
little to no activity onshore. This seems plausible since there
should be subsidence along the coast in the wake of the precipitation
area. This subsidence subsides by this afternoon which should allow
for potential shower development along the coast which is supported
by coarser models. But drier air aloft should move in by then keeping
any development isolated. Winds will become light southeast-SW by this
afternoon at the coastal terminals and NE at kflo/klbt.
VFR this evening with winds becoming light and variable. Some tempo br
possible coastal terminals overnight but confidence is low.
Extended outlook...predominantly VFR through the period with a
slight chance afternoon shra/tsra.
near term /through tonight/...
as of 1030 am Saturday...no changes to the coastal waters forecast
with the middle morning update. Essentially light and variable winds
as the synoptic forcing is weak...to be expected on this first day
Short term /Sunday through Monday night/...
as of 300 am Saturday...weakening stationary boundary will be
dissipating just inland from the waters this period. The gradient
will remain weak in the vicinity of this boundary Sunday...so
after a brief period of light north winds Sunday
morning...directions will shift to the S/southeast late Sunday but only
at around 10 knots. As Bermuda high pressure redevelops on
Monday...the gradient will tighten as the front continues to
weaken...and SW winds will increase to around 15 knots. Although
winds will be light Sunday...a long period (11 sec) southeast swell will
exist in the spectrum with a 2-3 feet amplitude...likely from the
long fetch around the offshore Bermuda high. This will allow wave
heights to be 3-4 feet Sunday. On Monday...this swell will combine
with a more significant wind wave to drive seas to 4-5 feet.
Long term /Tuesday through Wednesday/...
as of 300 am Saturday...Bermuda high pressure will be the dominant
feature through middle-week as a typical summertime pattern develops.
This high will be centered well offshore so the gradient is expected
to remain fairly benign...and winds will be SW at 10-15 knots with
little fluctuation both days. These winds will create a 5-6 second
wind wave...which will combine with a 2 feet southeast swell to create 3-4
as of 200 am Saturday...minor coastal flooding is possible during
the night-time high tide over the next couple of days. These
higher than normal tides are the result of the perigean Spring
tide and a full moon which occurred on Friday. Departures of plus
1/2 to 1 foot will be enough to produce a brief period of minor
coastal flooding. The risk is highest for portions of the lower
Cape Fear River to include downtown Wilmington...with a likely
probability. The beaches will approach the threshold for minor
coastal flooding again this evening...but this will be the last time
this lunar cycle.