Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington NC
811 PM EDT Friday Jul 31 2015
a weak front will wave across the coastal Carolinas this
weekend...producing scattered showers and thunderstorms near the
coast Saturday. The front should dissipate Sunday night. Bermuda
high pressure well offshore will build westward next week.
Near term /until 6 am Saturday morning/...
as of 730 PM Friday...basically the forecast area from the I-95
corridor to the coast will be under the gun this evening for the
continued threat for convection. The pinned sea breeze and the
cold front just inland from the coast provided the necessary surface
convergence by middle-afternoon once the available cape was achieved
by the days insolation. Combined with outflow collisions from the
ongoing convection...could see an additional solid 2 to 4 hours of
additional convection over land. By midnight and continuing through
the Sat pre-dawn hours...will see nocturnally driven convection over
the adjacent Atlantic waters take charge. And for that
reason...have kept atleast a chance pop for the immediate coast
after midnight. As you travel inland after midnight...probability of precipitation will
lower to no chance by the time you reach the I-95 corridor. With
no robust movement with the ongoing precipitation...the threat for flooding
will continue and thus have added the heavy rain attribute to the
ongoing convection. Overnight mins still look aok.
as of 300 PM Friday...convection finally starting to develop
across the area. Elements remain in place for at least some decent
coverage through the late afternoon and early evening hours. Good
coverage is still advertised by the latest NAM and to a lesser
extent the hrrr. I have walked back probability of precipitation slightly to adjust for
this. The NAM and GFS keep things active overnight with what
appears to be middle level deformation working on the low level
boundary so showers and thunderstorms cannot be ruled out
basically from this point forward. Overnight lows should dip to
the lower to middle 70s.
Short term /6 am Saturday morning through Sunday night/...
as of 300 PM Friday...by my count this is the fourth front to
make its way into coastal north and South Carolina this July.
While probably not a record it certainly seems unusual. The front
will oscillate back and forth across the area this
weekend...driven inland by the seabreeze and pushed back toward
the coast by the late night landbreeze. The southern periphery of
an upper level trough extending southward from Hudson Bay will
poke down into the Middle- Atlantic States...punching a hole the 500
Deep moisture will linger along the coast Saturday. This should
give rise to good coverage of showers and thunderstorms during the
afternoon for locations within 40-50 miles of the coast...very
near the location of the stalled front and potential seabreeze
zone. Westerly middle-level winds will tend to push storms eastward
toward the beaches. Farther inland for the I-95 corridor drier
air mixed down into the deep daytime boundary layer should lead to
convective capping and very little (if any) convection. Highs middle
90s inland to upper 80s coast.
For Sunday the front will still be lingering across the area...
however the middle-levels are quite a bit drier. This should lead to
even less coverage of storms...even along the coast where 850-700
mb layer relative humidity will fall below 50 percent. Highs
again middle 90s inland to around 90 at the coast.
In terms of model preference...the 12z GFS appears better
temperature and moisture-wise than the NAM and has fewer
spurious convective blowups...particularly given the lack of
upper disturbances in the 500 mb flow.
Long term /Monday through Friday/...
as of 300 PM Friday...surface and upper troughiness in place on
Monday though models look a bit quicker in shunting the deepest
moisture off the coast. Have preserved the inland/coastal gradient
but tweaked probability of precipitation down slightly. The upper level trough also looks
to lift out a bit faster on Tuesday so rainfall may be even harder
to come by and just isolated probability of precipitation area-wide. Wednesday also looks
fairly quiet with any energy impinging upon US from the west to
occur late in the day or at night. The Carolinas will then end up
in a regime of increasing flow aloft with embedded impulses that
tend to strengthen with time. Rain chances should be on the rise
though deep layer moisture may be hindered by the west-
northwesterly middle level flow. Deeper moisture in a southwesterly
flow aloft may be relegated for just after the long term. The
midweek days wherein a weak ridge builds aloft should feature some
heat but seemingly not the very hot readings found in the mex MOS.
Aviation /00z Saturday through Wednesday/...
as of 00z...a cold front was located just across the coastal
counties of NC/SC and has interacted with the sea breeze front to
trigger convection. Scattered showers and thunderstorms have
affected kilm mainly with some thunderstorms in the vicinity around kcre. Activity starting
to wind down across NC and increasing across SC...especially well
south of kmyr. Will carry showers and ts around the coastal
terminals for the next couple of hours winding down after 03z.
MVFR conditions in fog being forecasted for coastal terminals and
VFR for inland terminals well behind the front with drier airmass
across klbt and kflo. Front hangs off the coast for Saturday and
can see more scattered shower and ts activity as numerous
boundaries and moisture pooling along this region will help fire a
up activity on Saturday. MVFR across the coastal terminals for
Saturday with VFR conditions across the the inland terminals.
Extended outlook...predominantly VFR through the period with a
chance afternoon rain showers/thunderstorms and rain through Monday.
near term /through tonight/...
as of 745 PM Friday...synoptic SW winds have been infected by
outflows from the ongoing convection near shore this evening.
Expect this to continue the remainder of this evening and
especially overnight as convection further flares up across the
area waters. This due to a meandering frontal boundary
positioned just inland from the coast. Overall...still looking at
SW winds 10 to 15 knots...with few gusts up to 20 knots especially from
10-20 nm out. Significant seas will range from 2 to 4 feet...with 4
footers primarily occurring in the vicinity of Cape Fear and
southward. Wind driven waves at 4 to 5 second periods will mainly
dominate...but a slowly building 1 to 3 foot southeast pseudo ground
swell at 8 second periods will occur towards daybreak Sat.
as of 130 PM Friday...winds are now shifting back to the
southeast along the coast and this flow will allow the synoptic
flow of southwest to redevelop as the cold front pushes back
inland. The southwest flow of 10-15 knots will continue overnight.
Seas will be 2-4 feet.
Short term /Saturday through Sunday night/...
as of 300 PM Friday...a stalled front will wave back and forth
across coastal north and South Carolina this weekend...pushed
inland by the seabreeze circulation and pulled back down to the
beaches by the late-night landbreeze. If it wasn't for this front
Bermuda high pressure well offshore would provide a steady south-
southwesterly wind across the area. Light westerly winds Saturday
morning will turn back to the south during the afternoon as the
seabreeze/front moves inland. Winds late Saturday night will again
turn offshore...with winds shifting back to the south again Sunday
In addition to local wind waves there will be an 11-second
southeast swell developing this weekend. The combination of these
various wave sets will lead to 2-4 foot seas this weekend...lowest
along the coast during the morning hours. There is some potential
of 5-footers showing up during both Saturday and Sunday evenings
out beyond 15 miles from shore near Cape Fear.
Long term /Monday through Wednesday/...
as of 300 PM Friday...conditions will be fairly unchanging
through the period with southwesterly winds in the 10-15kt range
expected throughout. Bermuda high pressure and a Piedmont trough
will be driving these winds. A strengthening of the latter could
add a few knots of wind very late in the period. Seas will average
3 to 4 feet throughout.
as of 800 PM Friday...minor coastal flooding is possible during
the night-time high tide over the next few days. These higher
than normal tides are the result of the perigean Spring tide and
a full moon which occurs today. Departures of plus 1/2 to 1 foot
will be enough to produce a brief period of minor coastal
flooding. The risk is highest for portions of the lower Cape Fear
River to include downtown Wilmington...with a likely probability.
However...during this cycle...even the beaches have a small risk
for minor coastal flooding. High tide tonight is about 800 PM at
the beaches and about 1030 PM in downtown Wilmington. A coastal
Flood Advisory has been issued for the Cape Fear River from
NC...coastal Flood Advisory until 11 PM EDT this evening for ncz107.
... Rip current risk in effect from 7 am EDT Saturday
morning through 8 PM EDT Saturday evening for ncz110.