Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington NC
213 am EDT Monday may 4 2015
the center of a high pressure system will drift slowly offshore
through early this week...providing sunshine and seasonable may
temperatures. A coastal low is expected to form in the Bahamas
mid-week...and meander along the southeast coast through the end
of the week and into next weekend.
Near term /until 6 am this morning/...
as of 130 am Monday...dry and seasonable weather will continue
overnight as high pressure slips further off shore with a light
return flow providing a slight increase in moisture. There will
be plenty of subsidence and dry air through the middle to upper
levels with only limited low level moisture through the column as
middle to upper ridge tries to build overhead. It will be disrupted
by a shortwave riding down in the northwest flow aloft which will
reach the central Carolinas by day break. This should not produce
anything more than some middle to high clouds. The air mass will
continue to modify in east-southeast return flow as surface high shifts farther
east through the early morning hours. This will allow for modest
moisture return with dewpoint temperatures reaching back from lower 40s
this afternoon up to the middle 50s overnight. Expect temperatures to slow
down and remain in the middle 50s most places. Also expect patchy to
areas of fog as temperatures and dewpoint temperatures converge under light to
calm winds and limited cloud cover.
Short term /6 am this morning through Tuesday night/...
as of 3 PM Sunday...seasonable may sunshine on tap this period
with weak low-level onshore flow and dry air perched above 600mb
and light winds aloft. Weak short-wave impulses will meander over
the area as noted in 700 mb-500 mb vorticity fields but without fanfare
other than moderate cumulus build-ups with assistance from may
sun angle and resulting afternoon insolation. Maximums a few degree
either side of 80 warmest inland...and minimums in the upper 50s
to low 60s closer to the coast. Tuesday looks warmer over the
interior as the upper ridge becomes slightly more established.
Long term /Wednesday through Sunday/...
as of 3 PM Sunday...the entirety of the long term will focus on
what is expected to become a hybrid/sub-tropical low off meandering
off the southeast coast. Large area of disturbed weather will move
out of the Caribbean and then strengthen into a low pressure system
well offshore. This occurs in a region of very weak steering flow in
the vicinity of a large middle-level ridge across the southeast...and
thus there is very little confidence in what this system will do
once it develops...and guidance is all over the place in how the low
will track. However...there is increasing confidence that a hybrid-
low will develop...becoming warm core and likely strengthening
thanks to a combination of latent heat release from 80 degree waters
in the Gulf Stream...baroclinic instability due to change in water
temperatures near the coast...and good ventilation through diffluence
aloft. Will not make any wholesale changes to pop/weather in the extended
due to such low confidence...and will maintain the inherited pop for
the Thursday-sun timeframe...highest chance at the coast. Still...cannot
focus on any specific day being the most favorable for precipitation as the
guidance envelope is so wide. On the bright side...temperatures through the
period should be above climatology...especially away from the coast.
Aviation /06z Monday through Friday/...
as of 06z...not much synoptically different from yesterday...with
high pressure offshore giving US southeast flow. There is fog
potential again overnight...mainly after 08z. Cre stands the best
chance again...but could not rule out inland fog either. Do not
think we will see the LIFR conditions that we experienced last
night. Monday...becoming VFR at all locations with continued
southeast flow...strongest along the coast.
Extended outlook...pre-dawn morning fog is possible each day that
could result in MVFR/IFR conditions. Unsettled weather Thursday
night through Saturday with a subtropical low.
near term /through tonight/...
as of 130 am Monday...high pressure will shift farther off shore
overnight. Therefore expect a very light return flow to continue
basically less than 10 kts. Seas will run under 3 feet most waters
with a a very slow decline through tonight with such light winds
and diminishing longer period backswell from low moving off into
the distant Atlantic waters.
Short term /Monday through Tuesday night/...
as of 3 PM Sunday...friendly marine environment expected this
period as light onshore flow prevails with minimal wave energy.
A moderate afternoon sea breeze may drive onshore gusts to 17 knots
inshore accompanied by moderate chop...otherwise onshore 10 knots
Mon/Tue. With light chop and weak swell dominant wave period of
7-9 seconds expected...except inshore during the afternoon the
chop may briefly become the primary energy. No thunderstorms or visibility
restrictions expected Monday or Tuesday.
Long term /Wednesday through Friday/...
as of 3 PM Sunday...all eyes will be on a hybrid-type low
pressure system developing well off the southeast coast. This low
is expected to begin formation Wednesday...and then strengthen
slowly while meandering in weak steering flow. Still much
uncertainty regarding this portion of the forecast...but consensus
at this time keeps winds east/NE through the period with speeds
primarily 10-15 kts...higher at times. Of course...these could
change significantly depending on how this storm system evolves.
Prolonged east/NE fetch combined with the elevated winds will drive
seas up from 3-5 feet Wednesday...to 4-7 feet Thu/Fri...and an
extended Small Craft Advisory may be needed for much of the period.