Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 290534

Area Forecast Discussion
National Weather Service Wilmington NC
132 AM EDT Thu Sep 29 2016

A cold front approaching from the west will slow down on Friday and
linger near or along the Carolina coast through this weekend. High
pressure will build in behind the front through early next week.


As of 1030 PM Wednesday...Forecast area remains clear of
convection this evening. However, a second round of convection is
possible as a vorticity lobe streaks up from the south, embedded
in the mean flow between the Atlantic Ridge and deep closed low to
the west. Elevated instability will remain, and forcing within
this vort will be enough to cause more showers with isolated tstms
tonight, and this may affect a larger portion of the CWA than will
be impacted through this eve. Do not expect strong or severe
overnight, but more showers will be possible and have continued
CHC Pop through the overnight. Temperatures overnight will remain
above seasonable norms, with mins dropping only to around 70.


As of 300 PM Wednesday...Synoptic pattern changes very little
through the end of the week, although sensible weather will improve
through the period. Deep upper low across the OH VLY will remain the
dominant feature as flow becomes very slow, keeping the closed low
basically stationary through the period. This will cause a cold
front to move slowly to the east, but guidance has backed off even
further on this motion, and it is now progged to not quite make it
to the coast even by Friday night. This will keep unsettled weather
with warmer temperatures across at least the eastern third of the
CWA, while locations out towards i-95 should still break into the
drier and cooler air, especially on Friday. This is noted by much
lower RH above 850mb advecting eastward in a dry slot beneath the
upper low. However, the large ridge across the Atlantic remains
strong, and forces the moist air ahead of the front and the dry slow
to remain along the coast, while the pinched flow between these
features drives vort impulses and shower chances northward into the
region. Friday will overall be a drier and slightly cooler day than
Thursday, that will be most felt well inland, while the immediate
coast may see little change with above climo temps and scattered
aftn convection.


As of 300 PM Tuesday...Latest model run keeps deep cutoff upper
low a bit farther west as it tracks up toward the Great Lakes over
the weekend. Therefore the sfc front and deeper moisture should
remain aligned parallel, just along the coast rather than off shore.
Plenty of dry air will wrap around the upper low into the Carolinas
aloft, but the lower dewpoint air behind the sfc boundary may
struggle to make it to the coast. Also, the sfc boundary will remain
a focal point for convective development and although the air aloft
will be drier, there should still be shallow convection possible
along and east of the boundary. There will be a sharp gradient
between the drier air to the west and moister air to the east, but
exactly where that will lie is tough to say. The models are trending
on keeping the boundary farther west, along the coast, rather than
off shore. This will mean more clouds, showers and more humid air in
place over the eastern half or third of our area, but as you move
inland there will be greater amounts of sunshine and drier air. The
latest pcp water shows values up close to 2 inches from the tip of
Cape Fear up to Hatteras while west of I-95 will have PWATS less
than an inch with even lower amounts as you head W-SW. Essentially,
the drier air will wrap around from the SW aloft and N-NW at the sfc
and it will be more of a dewpoint gradient rather than temps.
Daytime highs will remain in the 80s most places. The guidance has
backed off on the cooler overnight lows due to the lack of lower
dewpoint air moving in, but I still think many places inland will
get down toward 60 early Sat.

As the the mid to upper low lifts north Sunday through early next
week, the lingering boundary will be pulled farther back on shore as
it dissipates through Monday. The winds should shift around to the
NE to E bringing some moister air back inland. Overall, places
inland and west of surface boundary will see a greater amount of
sunshine while places east of boundary will see a greater amount of
clouds and chc of pcp.

Heading into the middle of next week, the forecast become further
complicated by the differences in the models as to the track and
timing of Tropical Cyclone Mathew. For now, this system looks like
it will track westward and eventually turn up around the Atlantic
Ridge. The GFS is much faster with this system and we will have to
see how this evolves to determine how or if this affects the
southeast coast. For now, the greatest effects may be over the
coastal waters in pulses of swells and increasing gradient winds
eventually drive up the seas.


As of 06Z...Rather persistent storms just west of our area and the
HRRR wants to spread them all the way to the coast by daybreak. This
seems ambitious but have covered for this possibility with VC.
Better chance for predominant rain is at FLO and LBT. Then there may
be a break in the action before daytime heating causes isolated
storms to fire through the day as front remains stalled to our west.
By evening a large scale dry slot should be spreading into the area
shutting down any rainfall from SW to NE though a few may linger at
the coast.

EXTENDED OUTLOOK...Primarily VFR. Isolated to scattered afternoon
showers through much the period, although limited in strength and
coverage due to dry air aloft.


As of 1030 PM Wednesday...Latest obs continue to show SE winds of
around 10 kts with 3 ft seas. Forecast in good shape with no
changes needed. Previous discussion follows:

Stalled front continues to sit NW of the waters, with a weak
pressure gradient remaining in place. Winds will slowly veer from
present S/SE to SW overnight, along with a slight increase in
speed from 5-10 kts to a more uniform 10 kts. This will create
seas of 2-3 ft, with a southerly wind wave and low amplitude SE
swell comprising the spectrum. Showers with isolated tstms will be
possible across the waters late tonight as well.

As of 300 PM Wednesday...Slow moving cold front will drag west to
east through the short term, finally approaching or stalling across
the waters Friday night. This will keep the waters in the warm
sector with S/SW winds of 10-15 kts expected through most of the
period, possibly shifting to the W/NW Friday night. These persistent
winds combined with the offshore high pressure will keep a 5-6 sec
southerly wind wave and 9-10 sec SE swell in the spectrum, creating
2-3 ft seas.

As of 300 PM Tuesday...A cold front will run parallel along or
near the Carolina coast...weakening through early next week.
Overall expect more northerly winds on west side of front to come
around to the NE to E as weakening boundary gets drawn back westward
as upper low lifts off to the north through the period, but great
variability is possible. Southerly winds should continue to the east
of the boundary. Seas will generally remain 2 to 3 ft over most
waters but a slight rise will be seen due to some longer period SE
swells mixing in through the weekend into early next week.





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