Area Forecast Discussion
Issued by NWS Wilmington, NC-- Remove Highlighting --
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FXUS62 KILM 300905
Area Forecast Discussion
National Weather Service Wilmington NC
505 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/...
-- Changed Discussion --As of 415 AM Friday...The cutoff low begins to very slowly fill as
it lifts to the north reaching the Eastern Great Lakes by the end
of this short term period. The direct affect from this cutoff low
will lessen with time. Models in agreement with the stalled sfc
front lying along or just off the coastline of the Carolinas. And
the dry air extending just shy of the immediate coast. Thus the
challenge of fcsting daily sfc temps and dewpoints. The moist air
will extend from the stalled front and offshore. The main
baroclinic zone and associated convection, to lie offshore from
SW to NE, parallel to the Carolina coastlines. Have indicated low
pops for the immediate coast to account for any onshore movement of
pcpn each night, and any development along the stalled front
during each day. As for temps, stayed closed to a consensus
amongst the avbl Mos Guidance with a slightly higher bias for max
temps each day. This will result in daily max temps a category
higher than climo norms and daily Mins 1 to 2 categories above the
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.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 /09Z 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.
-- Changed Discussion --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 /SATURDAY THROUGH SUNDAY NIGHT/...
As of 415 AM Friday...This time period will feature a stalled
frontal boundary either along the immediate coast of the Carolinas
or just offshore and parallel to the coastline. Thus the challenge
of either keeping winds from the S-SW or eventually having winds
become nearly variable in direction during this period. As
always, will try to acknowledge a dominate wind direction in lieu
of going variable. The sfc pg remains rather semi-relaxed thruout
this period, yielding either 5-10 kt or 10-15 kt. The latter will
occur at the beginning of this period and becoming 10 kt or less
as this period progresses. Significant seas will run around 3 ft
thruout this period. Wind driven wave input into the significant
seas will lower during this period. However, an easterly 2 to
possibly 3 foot ground swell at 10 to 12 second periods will
become the dominate input into the significant seas equation
during the day on Saturday and persisting thru Sunday night.
This illustrated nicely by Wavewatch3.
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.
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