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Area forecast discussion 
National Weather Service Wilmington NC
644 am EDT sun Sep 21 2014

Synopsis...
deepening low pressure offshore will move northeast away from the
area this morning...leaving dry and warm conditions by this
afternoon. A cold front will cross the area early Monday with
isolated showers and thunderstorms. Much cooler air will follow
for the middle of the week. A trough will sharpen offshore and
move towards the coast...bringing increasing rain chances for the
latter part of the week.

&&

Near term /through tonight/...
as of 630 am Sunday...deepening low pressure east of Cape Lookout
will accelerate out to the northeast today...taking clouds and
residual light rain along with it. Much drier air throughout the
atmospheric column will work into the eastern Carolinas by late
morning with precipitable water values falling from 1.5 to 2
inches down to near 1 inch by noon. The bubble of cool air along
the back side of the low will be a fading memory by this afternoon
as westerly downsloping flow off the southern Appalachians
rebounds 850 mb temperatures to +17c. With nearly full sunshine expected
by noon highs should reach the upper 80s inland with middle 80s at
the coast...approximately 10 degrees warmer than yesterday.

As we move deeper into September (and meteorological autumn) the
synoptic pattern does not resemble Summer anymore. An active polar
jet across the Great Lakes and northeast will whip another upper
disturbance eastward into the Appalachians tonight. The surface
reflection of this will be a cold front pushed southeastward by high
pressure over the Central Plains. This front should arrive in the
eastern Carolinas by daybreak Monday...accompanied only by a wind
shift at the surface since the low or middle level winds should not
back enough to promote moisture advection from the Atlantic or Gulf.
A modest low level jet should add enough wind to the boundary layer
to keep low temperatures near the warmer NAM MOS numbers.

&&

Short term /Monday through Tuesday night/...
as of 300 am Sunday...Monday brings the last day of astronomical
Summer...as the fall equinox occurs around 1030 PM Monday night.
Right on cue...a fall-like cold front will cross the area during
Monday...ushering in true fall-like air for Tuesday. Before the cool
dry air can overspread the Carolinas...showers and thunderstorms are
expected along the cold front Monday afternoon. Although moist advection
ahead of this feature is limited...the frontal passage temporally matching
peak heating should provide enough forcing for scattered
showers/tstms...with highest pop expected along the coast where the
deeper...yet still moderate...moisture will reside. Inherited
forecast has schc for Monday...and will make only minor upticks
along the coast. Precipitation will wane quickly after dark thanks to loss
of heating and the cold front moving further away...allowing for
rapid cool/dry advection to engulf the area. This will leave a
beautiful...although a bit windy...fall day on Tuesday as expansive
Canadian high pressure ridges down from the Great Lakes.

Although sunshine will be plentiful on Tuesday...highs will struggle
on continued...but weakening...caa...leaving highs in the upper
70s...a few degrees cooler than those expected Monday. Mins both
nights will drop to some of the coolest values we have seen in a
while...with middle/upper 50s expected inland...and right around 60 at
the coast.

&&

Long term /Wednesday through Saturday/...
as of 300 am Sunday...stalled cold front offshore will transition
into a coastal trough...aided by developing shortwave energy
middle-to-late week. This will combine with a strengthening high
pressure wedge just inland of the coast to produce cool and
increasingly unsettled weather during the extended. Although there
is still some disagreement among the deterministic models about the
amount of clouds/precipitation expected...they are all more pessimistic in
their solutions for late week.

Deep easterly flow through at least half the atmospheric column will
advect ample moisture towards the Carolinas...while at the same time
driving the coastal trough towards shore. This combining with the
aforementioned vorticity energy aloft may even spawn weak low
pressure...all of which point to deteriorating weather conditions
locally. Cool east/NE winds at the surface with easterly flow topping
that will create widespread low-cloud cover and periods of
showers...with the best chance along the coast late in the week as
isentropic lift amplifies. With a strong wedge in place and a
strengthening coastal trough in the vicinity...the first week of
fall looks to take on a decidedly winter-like feel with
clouds...periods of rain...and temperatures below climatology.

Drying should finally begin by the weekend as ridging develops
aloft...squelching the coastal trough and eroding much of the middle
and upper level moisture.

&&

Aviation /12z Sunday through Thursday/...
as of 12z...low pressure offshore is now tracking away from the
region...taking the deep moisture along with it. Some IFR ceilings
remain at ilm...with some lingering showers at The Myrtles. VFR
condtions will prevail at all terminals in a couple of hours. Winds
already northwest and this will continue with some gustiness
throughout the day. Diminishing winds this evening as they back to
the southwest.

Extended outlook...VFR through Wednesday with a chance of a shower with a
cold front on Monday.

&&

Marine...
near term /through tonight/...
as of 630 am Sunday...deepening low pressure east of Cape Lookout
will accelerate out to the northeast today...taking the rough
weather of the past 24 hours with it. Lingering light rain near and
north of Cape Fear should end no later than 9 or 10 am with dry
weather expected through tonight. Behind this low the strongest
offshore winds should occur around daybreak this morning...expected
to reach 25 knots sustained away from shore in the Cape Fear area.
Seas up to 7 feet away from shore may continue into late
morning...and the Small Craft Advisory will remain posted.

Winds will back more westerly this afternoon...then southwesterly
tonight with another increase in speed expected as a low level jet
organizes out ahead of a dry cold front that will reach the water
Monday. While winds/seas should remain below advisory levels tonight
it's just one more sign that the seasons are changing.

Short term /Monday through Tuesday night/...
as of 300 am Sunday...westerly winds around 10 kts will start the
period...before a cold front crosses the waters during Monday afternoon.
This will cause a wind shift to the north Monday evening...with
further veering to the northeast occurring Monday night. As these
winds become from the NE...they will be accompanied by a
strengthening surge with wind speeds rising to 15-20 kts. High
pressure ridging down the coast on Tuesday...combined with this cold
front stalling offshore...will keep a pinched gradient...and NE
winds will steadily rise to 20-25 kts throughout Tuesday. Seas
through the daylight hours of Monday will be 2-3 feet with a variable
wind direction causing a confused spectrum. Beginning Monday night
however...as the NE surge develops and persists...seas will build
from 2-3 feet to 4-6 feet...and a Small Craft Advisory will likely be
needed beginning Tuesday night.

Long term /Wednesday through Thursday/...
as of 300 am Sunday...high pressure will ridge down the coast
through the period...while a coastal trough strengthens offshore.
This creates a pinched gradient both Wednesday and Thursday...driving
persistent and strong NE winds of 20-25 kts into late week. These
winds will drive seas to 4-7 feet through the coastal waters...with
the exception being along the near-shore waters of amz252 and amz254
where wave shadowing is likely and amplitudes will thus be lower.
Even so...an extended Small Craft Advisory is expected during this
period.

&&

Ilm watches/warnings/advisories...
SC...none.
NC...none.
Marine...Small Craft Advisory until noon EDT today for amz250-252-254-
256.

&&

$$

Synopsis...jdw
near term...tra
short term...jdw
long term...jdw
aviation...43
marine...tra/jdw

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