Area Forecast Discussion
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FXUS62 KILM 300821
Area Forecast Discussion
National Weather Service Wilmington NC
421 AM EDT Fri Sep 30 2016
A stationary front will waver along the coast through this
weekend. Periods of showers with an isolated thunderstorm are
possible along this front. Weak high pressure will build in
early next week. Hurricane Matthew may bring increasing waves
by the middle of next week.
.NEAR TERM /THROUGH TONIGHT/...
As of 330 AM Friday...The expansive cutoff Low centered over
Kentucky will be the main show affecting the ILM CWA this period.
The latest HRRR, RAP and HiResWrf models, all indicate to a
degree, the current pcpn breaking out and further increasing in
coverage and intensity during early this morning and continuing
thruout the day. This a result of dynamics from elongated mid-
level vorts from the tropics passing nearly overhead, the sfc
frontal boundary aiding low level forcing, and copious amounts of
moisture with flow from the sfc thru aloft mainly southerly
straight from the tropics. With the days heating and sfc based
instability becoming available, convection should breakout
further. The dry slot/tongue rotating around the cutoff low, will
slowly push the pcpn toward the east whereas the individual
showers and storms will be racing to the north. The back edge of
this main area of pcpn should push just east of the ILM CWA by
early this evening. Locations especially west of the I-95
corridor, will actually see drier air and lower temps due to the
dry slot. How much of this drier air and lower temps work eastward
are 1 of the main challenges of this forecast. For the overnight
period, have left a low POP along the immediate coast, basically
in the vicinity of where the stalled frontal boundary ends up.
At this point, have indicated in the Hazardous Weather Outlook
that heavy rainfall from todays convection will have the potential
to produce temporary flooding especially susceptible areas having
experienced a good dose of rainfall during the past few days.
.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
As of 345 PM Thursday...Little change in the synoptic setup into the
weekend as bowling ball of the upper low spins slowly across IN/KY
before lifting into OH late in the period. At the surface, a very
slow moving cold front will push eastward, likely finally crossing
offshore Friday night before stalling once again. With diffluence
remaining east of the upper low, and low level confluence likely
persisting along and east of the boundary, more convection with
periods of heavy rain is forecast Friday. The best chance for
rainfall will again be the eastern third of the CWA where mid-level
RH remains elevated despite a very dry punch within the dry slot
working into the Pee Dee. This creates 2 distinct air-masses across
just the local CWA, with PWATS forecast to drop below 1 inch well
inland, while remaining at 1.5-1.75 near the coast, and inland
counties may finally have a dry day Friday. By Saturday, most of the
CWA is forecast to get into the drier air, but once again the
immediate coast may still see no relief from this humid airmass with
more showers/tstms possible along the coast.
Highs both Friday and Saturday are forecast to be slightly above
climo, low 80s, but will be heavily impacted by clouds and rainfall.
Mins inland will drop into the upper 50s/low 60s both nights within
that drier air mass, but will remain near 70 at the coast.
.LONG TERM /SUNDAY THROUGH THURSDAY/...
As of 3 AM Friday...Temperatures will be quite seasonable to
slightly mild and rain chances minimal through the long term.
Moisture associated with frontal remains lingering offshore on
Monday and low level onshore flow could advect the stray shower to
mainly coastal areas. Weak upper troughiness may aid the coverage of
showers even though mid levels probably dry. Beyond Monday this
troughiness gets replaced by a slowly amplifying ridge and this
should cut down on the already paltry radar coverage. This low
coverage will be confined to coastal areas while inland zones stay
dry. Low level moisture trapped beneath the inversion will favor a
bit more in the way of clouds than `normal` through the period.
Currently it appears that Matthew stays far enough east to only have
marine effects locally. The GFS has been a very fast outlier from
other guidance though now Canadian is even faster. The EC has
shifted a bit farther east from previous runs. The overnight RI is
allowing convection to wrap around the center and so models may show
some improvement with the system stacking in the vertical.
.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
As of 06Z...Patches of IFR or lower now becoming less widespread
ahead of approaching pre-frontal band of showers and should remain
so for the rest of the overnight save for perhaps LBT where so much
rain fell recently. Showers streaming onshore to increase in
coverage predawn but only tend to MVFR with any IFR dips too brief
to warrant being in TAFs. Dry slot sweeps west to east across the
area this afternoon and clears things out. Slight chance of very
minor visibility restrictions returning Friday night.
EXTENDED OUTLOOK...Primarily VFR. Isolated to scattered afternoon
showers through much the period, although limited in strength and
coverage due to dry air aloft.
NEAR TERM /THROUGH TONIGHT/...
As of 330 AM Friday...Sfc cold front across the inland Carolinas
will push to the coast late tonight and likely stall along the
immediate coast or just offshore Sat and subsequent periods.
This will be the dividing line for pcpn coverage. East of the
front pcpn will be more numerous and potent, and west of the
front isolated in coverage. Looking at S winds at 10 to 15 kt
today and SW 10 to 15 kt tonight, with speeds lower within the
actual frontal zone. Significant seas will be a healthy 3 to
possibly 4 ft, and comprised of mainly wind driven waves at 4 to 6
seconds. An underlying 1 foot ESE ground swell at 10-11 second
periods will be present.
SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 345 PM Thursday...A cold front will be west of the waters
Friday before wavering across or potentially still just inland on
Saturday. This creates predominantly S/SW winds of 10-15 kts on
Friday, backing to the SE around 10 kts on Saturday, again dependent
on where the front stalls. A period of variable winds is possible
late Friday into Saturday as the front drifts into the vicinity, but
speeds will be light during that time. Seas will hover around 3 ft
both Friday and Saturday with a low amplitude 9-10 sec SE swell and
2-3 ft 5 sec southerly wind wave comprising the spectrum.
LONG TERM/MONDAY THROUGH TUESDAY/...
As of 3 AM Friday...A northeasterly wind wave and increasing ESE
ground swell energy to cause a gradual rise in seas over the long
term. Tough to say how high the wind speed and resulting short
period seas get though as most model guidance is seemingly too fast
with Matthew. Winds may end up being reduced this period assuming
the slow movement of the currently favored EC model comes to pass.
The aforementioned swell energy is less related to Matthew and more
energy from the long fetch developing. Any Matthew swells (and there
will be some!) may be slated for just beyond the long term.