Area Forecast Discussion
Issued by NWS Wilmington, NC-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS62 KILM 222240
Area Forecast Discussion
National Weather Service Wilmington NC
640 PM EDT Thu Sep 22 2016
-- Changed Discussion --Weakening low pressure will drift offshore of the Carolinas
through late Friday, taking the rainfall threat with it.
Weak high pressure accompanied by drier air will prevail on
Saturday. A modest cold front will drop south across the area
early Sunday. Modest high pressure will follow and ridge across
the area from the NE states through the early to mid week period
of next week.
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.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
As of 600 PM Thursday...POPs have been increased thruout this
evening with the going concern being the continued moderate to
heavy rain being produced by the convection. Lightning data has
been limited/sparse across the Carolinas and therefore will just
mention isolated thunder thru mid-evening. With the moderate to
heavy rain persisting well into this evening, unlike what the
latest HRRR and RAP indicate, have updated the pcpn phraseology to
include "heavy rain". In addition, with a half a dozen of Flood
Advisories issued, have updated the Hazardous Weather Outlook to
include the potential for temporary ponding or shallow flooding
from this evenings local heavy rains.
.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/...
As of 300 PM Thursday...Low pressure over the Cape Fear area will
weaken and move east through Friday as high pressure builds down
from the north. The main mid to upper trough will lift off to the
north and east and a ridge builds over the southeast, although both
the ECMWF and the GFS show a low cutting off from the main trough
and lingering across the deep south into Sun. A weak backdoor
front will make its way south through VA and into NC Sat night and
should reach into SC by Sun morning. Pcp water values up close to
1.9 inches on Fri mainly aligned along the SC/NC coast will
diminish to less than 1.5 inches by Sat aftn with drier air and
subsidence finally scouring out the remaining moisture from this
persistent remnant low from Julia. Therefore, will continue with
higher pops and greatest chc of shwrs/tstms on Fri mainly east of
I-95 to the coast as sfc low remains just off the tip of Cape
Fear. Expect clearing to occur through late Fri into Sat as Dry
air and subsidence work there way south and east as upper ridge
builds east through Saturday. This should produce plenty of
sunshine across much of the area, but lingering moisture along the
coast should produce some cu and possibly some isolated showers
mainly over the SC coast Sat aftn. Not expecting much change in
the feel of the air mass with humid weather continuing. Clouds
will be tough to break on Fri with continued showers and therefore
expect high to be in the 70s much of the day, but places that
break out in the afternoon should reach into the 80s. Saturday will
warm well into the 80s with a good deal of sunshine across much of
the area. Overnight lows will be in the mid 60s to around 70.
.LONG TERM /SUNDAY THROUGH THURSDAY/...
As of 300 AM Thursday...A mid-and-upper level ridge axis will
shift from the TN valley Sunday to the east coast by Tuesday, and
will amplify between two anomalously strong upper lows into a
Omega block-type pattern. At the surface, high pressure will
ridge down across the mid-Atlantic states and produce onshore
flow through the period. Although the primary belts of deepest
moisture will remain south and west of the area, persistent
onshore flow below 850 mb would provide sufficient moisture to
support scattered showers.
.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
As of 18Z...Expect at least tempo mvfr conditions into the evening
hours in scattered showers and thunderstorms. conditions are
expected to deteriorate to ifr levels again tonight with a slow
transition after sunrise to vfr or mvfr conditions. light, mainly
northeast to east winds are expected through the taf period.
EXTENDED OUTLOOK...Isolated to scattered convection, mainly during
the afternoon and evening hours is possible beneath the cutoff upper
low through Friday. MVFR/IFR morning stratus/fog possible each day
through Saturday. Expect mainly VFR Sunday through Tuesday.
-- Changed Discussion --NEAR TERM /THROUGH TONIGHT/...
As of 600 PM Thursday...A relatively relaxed sfc pg will yield 10
kt or less wind speeds tonight. The progged sfc pressure field
itself paints the elongated sfc low, underneath the upper low,
straddling the coasts of NC and SC thru tonight. Could go variable
in direction especially with speeds only at 5 to 10 kt, but
instead will identify the more predominate directions, southeast
to south. Significant seas will primarily be driven by a 1.5 to
2.5 foot, e to ese ground swell from distant Tropical Cyclone
Karl. Latest Spectral Density Chart for 41013 indicates the ese
11-13 second period Karl swell is definitely driving the
Have increased the convection coverage this evening based on
latest KLTX 88D trends. In addition, have highlighted the
persistent convection over the northern-most waters oriented
parallel to Cape Fear, as it pushes northward and onshore.
Waterspout(s) has/have been sighted earlier today in the vicinity
of this pcpn. Will mention this waterspout risk until sunset in
the Hazardous Weather Outlook.
SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 300 PM Thursday...Low pressure just off the tip of Cape
Fear will finally move away as high pressure builds down behind
through Saturday. A cold front will drop south reaching NC Sat
night and should move through the waters by Sun morning. This may
be fairly transparent as winds will have already shifted to the
N-NE by late Fri as low weakens and shifts east. Therefore light
and variable winds on Fri will become northerly by early Sat and
will remain N to NE through Sat night increasing up to 15 kts.
Seas 3 ft or less will increase up to 2 to 4 ft into Sat night. A
longer period SE-E swell will continue through the weekend, up to
11 to 12 seconds.
LONG TERM /SUNDAY THROUGH MONDAY/...
As of 300 AM Thursday...Surface high pressure will build down the
eastern seaboard behind a cold front, which should be crossing
the waters during the day Sunday. With a blocked upper-level
pattern developing through the first of the week, the surface high
will persist and result in onshore flow through Monday. It does
still appear that 3-4 foot swells every 10 seconds will continue
into Sunday from distant tropical system Karl, falling off to a
2-3 foot wind wave by Monday.
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