Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington NC
339 PM EDT Thursday Aug 21 2014
hot and humid conditions will persist through Friday. A cold
front will sag southward across the area Friday night and
Saturday...bringing a higher risk for showers and thunderstorms.
Surface high pressure will follow from the north early next week
bringing more comfortable temperature and humidity levels.
Near term /through tonight/...
as of 330 PM Thursday...coastal convergence due to west-northwest flow off
the surface in a sultry and fueled air mass has allowed eruption
of torrential rain cores...primarily confined along the coastal
interior and the immediate coast. The sea breeze boundary as it
marches inland will spark more updrafts as the marine intrusion
deepens...so we will likely see new growth along and east of the
sea breeze front. No other triggers farther inland and the local
atmosphere remains hot and humid but so far still untapped over
the deep interior...where it could remain such.
Isolated severe cannot be ruled out completely into early evening
since surface based convective available potential energy will remain elevated along the east zones
as will the surface dewpoints. Any colliding boundaries will carry
a potential for pulse severe thunderstorms...as was noted in Holden Beach
earlier where dime to nickel size hail was reported.
Diurnal cooling into middle-evening or sooner should begin to show
and takes its toll on convective vigor...particularly with very
warm 500 mb temperatures in place. The buildup of low-level heat
however and the resultant buoyancy in the low-levels could sustain
cells through evening. Steering winds will guide storms slowly to
Mins by daybreak Friday...middle and upper 70s near the coast and
70-74 inland where partial clearing dewpoints in the 60s this afternoon
may allow decent falls overnight.
Short term /Friday through Saturday night/...
as of 300 PM Thursday...the strong middle and upper level ridge will
begin to retrograde...allowing a trough off the East Coast to dig
southward. This will allow a cold front to our north to sag
southward and we expect this front to slowly backdoor through the
forecast area Friday night and Sat. Shortwaves topping the amplified
ridge may serve to enhance the coverage and intensity of
convection and although timing is difficult at this juncture...
will show probability of precipitation trending to a higher probability Sat and Sat night.
The convection while still generally slow moving...should pick up
the pace this period as columnar winds increase slightly.
Friday should be the warmest day of the two and thus the most
uncomfortable. However...there appears to again be enough drier
air in the middle levels so that when mixing becomes deeper midday
and through the afternoon...dewpoints will again drop...with many
areas away from the immediate coast dropping to the upper 60s and
lower 70s. Thus...even with the intense heating...temperatures in the
middle and upper 90s Friday...it will be a struggle to meet heat
advisory criteria in most locations. The best chance for marginally
meeting criteria will be across the southern Pee Dee and perhaps
portions of the grand strand. At this time...will highlight the
heat and humidity in the severe weather potential statement...but refrain from issuing an
advisory. More widespread cloudiness developing Sat should help to
keep temperatures down a category or so...will go for widespread lower to
middle 90s. The seabreeze will move inland both days...more so on
Sat... keeping daytime highs lowest along the immediate coast.
Nighttime values across the forecast area will be a little above
climatology for late Aug.
Long term /Sunday through Thursday/...
as of 300 PM Thursday...middle to upper level pattern amplifies as the
ridge builds up from the Mississippi Valley into New England through
early next week and then expands eastward over the southeast coast
through the week. This will help to push cold front farther south
through Sunday as surface high builds down from the northeast
through the week. Expect lingering clouds and showers on Sunday to
shift south through the day as cold front moves south. Then the
building ridge should help to suppress any widespread or strong
convection through much of the week producing a quieter weather
period. Temperatures will be back down to normal behind cold front with
highs between 85 and 90 most days and overnight lows between 65 and
As for the tropical system approaching the Windward Islands
mentioned previously...the models remain fairly inconsistent as to
the exact track or intensity. The GFS was tracking it up into the
Gulf Coast a few days ago and then has progressively shifted east
now showing more of a track up through the Atlantic waters east of
coastal Carolinas later next week. The European model (ecmwf) has been the farthest
east and fastest model with the system. At this point decent swells
may reach our coastal waters by middle week but as far as weather...too
much uncertainty still exists.
Aviation /18z Thursday through Tuesday/...
as of 18z...sea breeze activity underway near the north coast. Will
add tempo group for a few hours along the coast. Brief heavy rain
probable. Tonight...light winds with some light fog possible after
midnight. The NAM has a convective complex coming over the
mountains...affecting the northern terminals overnight however
confidence is rather low with this scenario. Friday...a bit more
subsidence that previous day. Probably will see some isolated
convection...but that's about it.
Extended outlook...chance afternoon/evening rain showers/thunderstorms and rain through the
Sunday. VFR Monday. Showers possible near the coast Tuesday.
near term /through tonight/...
as of 330 PM Thursday...a weak stationary front inland should
maintain a light S-SW wind over the waters outside of thunderstorms. Winds
may drop several knots and back to SW overnight as the sea breeze
contribution fades out. Seas 2-3 feet in a mix south-southwest waves 1-2 feet
every 4 seconds and southeast waves 1-1.5 feet every 9 seconds. Mariners
should seek out a radar update before heading out since thunderstorms will
plague the waters through tonight.
Short term /Friday though Saturday night/...
as of 300 PM Thursday...SW winds will persist into Friday night. A
cold front will slowly sag south across the waters late Friday night
and Sat and this will serve to shift winds to a more northerly
direction and then more easterly Sat afternoon as the seabreeze
develops. Winds Sat night will back to NE and increase as a modest
surge develops southward across the waters. Highest wind speeds
will be Friday afternoon and night and then again overnight Sat...up
to around 15 knots. Seas will be 2 to 3 feet with some 4 feet seas
developing Friday night across the outermost waters. These 4 feet seas
will become more widespread from north to south late Sat night.
Long term /Sunday through Tuesday/...
as of 300 PM Thursday...high pressure will build down behind cold
front from the northeast through early next week. This will produce
a northeast surge in winds with persistent NE flow up to 15 kts
continuing through Monday. May see an increase in winds and seas by
Tuesday as a tropical system begins to make progress north helping
to tighten the gradient and increase winds and swells. For now will
show increase in seas up to 4 to 5 feet late Sunday into Monday and
then further increase possibly up to advisory levels by middle week.
SC...heat advisory until 6 PM EDT this evening for scz023-032-033-