Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington NC
1020 am EDT Sat Sep 5 2015
high pressure will ridge down from New England today bringing
cooler temperatures. This high pressure will persist into early
next week continuing somewhat below normal temperatures...but with
increasing chances for showers. A return to more typical late
Summer weather will develop Tuesday and persist through the end of
the week. A cold front will approach by next weekend.
Near term /through tonight/...
as of 1030 am Saturday...limited changes to the zones with the
morning update. The biggest challenge so far has been trying to
represent an erratic and dynamic cloud field. The latest NAM...12
UTC...continues to show a decent chance for probability of precipitation just inland
between about 20 UTC and 0000 UTC this evening. Therefore no
compelling reason to change probability of precipitation. The 1200 UTC mhx sounding shows
the considerable dry later around 800mb...the main impediment to
convection. Temperature trends look good.
Short term /Sunday through Monday night/...
as of 300 am Saturday...upper trough will close off and be forced to
retrograde from the western Atlantic Ocean back across the southeast
this period as large ridging blocks its progression to the north or
east. Beneath this feature...a surface trough will also back in from
the Atlantic and into the Carolinas Sunday into Monday...along with
higher precipitable waters from remnant tropical moisture pooled
from excessive-Tropical Storm Erika. All of these features together will
create a good chance for showers and thunderstorms...especially
during the aftns when heating of the day will help trigger
convection along the surface trough. However...at least schc pop
will be carried even at night due to high column moisture...the
surface feature...and relatively steeper lapse rates thanks to the
500mb trough overhead.
Temperatures both days will likely feature low diurnal ranges as cloud
cover and precipitation keeps mins above normal and highs below. Expect
lows each night to drop to 68-72...warmest at the coast...with
highs in the low 80s at the coast...middle 80s well inland.
Long term /Tuesday through Friday/...
as of 300 am Saturday...upper trough plaguing the southeast the
several days leading up to this period will slowly fill and
dissipate by middle-week as ridging develops near Florida and expands
to the north. While overall thickness increase will be
marginal...the erosion of the surface trough associated with the
building heights combined with Bermuda-type ridging will bring drier
and warmer conditions much of next week. Tuesday may still feature
above-climatology precipitation chances as it is the transition day...but Wednesday-Friday
will be more Summer-like with typical diurnal convective chances and
temperatures several degrees above climatology for both highs and lows. A cold
front will approach late in the period but for now will keep it just
northwest of the area until the weekend.
Aviation /14z Saturday through Wednesday/...
as of 12z...radar shows some showers in the Morehead City area
heading this way...however they will either dissipate or stay
offshore. Cooler northeast flow today with some MVFR ceilings likely
through middle morning...scattering after that. High pressure will
continue to ridge into the region through the afternoon hours with
only a slight chance for showers...mainly inland. Light northeast
flow will continue this evening.
Extended outlook...predominately VFR with brief MVFR and possibly
IFR...in morning fog...and isolated/scattered afternoon early
evening showers and thunderstorms mainly during the Sunday through
Tuesday time frame.
near term /through tonight/...
as of 1030 am Saturday...winds and seas look fine with regards to
the morning update. No changes. Previous discussion follows:
The Carolinas are on the southern edge of
1026 mb high pressure centered over New England. The pressure
gradient between this high and a weak trough of low pressure
extending east off the Florida coast will maintain a northeast wind
today and tonight. Wind speeds should be strongest this morning...
14-17 knots sustained...with wind speeds diminishing by several
knots this afternoon. 00z computer models are in good agreement with
wind speed and direction.
Seas currently 1-2 feet should build the most near and east of Cape
Fear due to the northeast fetch...with 3 foot seas expected there by
8 am. Seas should diminish back toward 2 feet tonight. Isolated
showers may develop later today...with better chances tonight.
Short term /Sunday through Monday night/...
as of 300 am Friday...surface ridge of high pressure will build down
the coast through the short term...while a coastal trough pushes
slowly inland beneath a middle-level trough. This will maintain NE
winds Sunday and much of Monday...with slight veering to more
easterly winds late Monday as the surface trough pushes inland.
Highest speeds this period will be Sunday when the ridge is
strongest and the gradient is pinched...as winds reach 15-20 kts
before falling back to 10-15 kts by Monday...and then below 10 kts
Monday night. The sea spectrum will be dominated by a 5-6 second NE
wind wave which will ease and lengthen into Monday...creating 3-4 feet
seas Sunday...dropping to 1-3 feet on Monday.
Long term /Tuesday through Wednesday/...
as of 300 am Saturday...high pressure expanding off the Florida
coast will drive a return to more typical summertime conditions
through middle week. Tuesday will be the transition day as winds veer
between east/NE early to south late...and then even further to SW on
Wednesday thanks to return flow developing around the surface high.
Although this variety of wind direction may cause a confused
spectrum Tuesday...wind speeds will be light around 10 kts...so wave
amplitudes will be 1-3 feet Tuesday. As the SW winds become dominant
Wednesday...seas will remain 1-3 feet but a ground swell will begin to
increase in amplitude within the spectrum.