Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 221037

Area Forecast Discussion
National Weather Service Wilmington NC
637 AM EDT Fri Sep 22 2017

A weak upper level disturbance could produce scattered showers
and thunderstorms again today. High pressure over the southern
Great Lakes will bring drier but continued warm air across the
Carolinas for the weekend. Hurricane Maria will move northward
through the Atlantic several hundred miles off the Carolina
coast next week, bringing strong rip currents and large surf to
the beaches, and hazardous marine conditions offshore.


As of 300 AM Friday...Weak high pressure resides over the area this
morning as an elongated trough extending from Jose down into
the southeast remains in place at the mid levels. There is some
dry air at the mid levels as seen on water vapor imagery moving
southward. This along with a very gradual push of dry air at the
surface will serve to limit convection somewhat as compared to
Thursday. We are still advertising slight chance pops mainly in
the South Carolina counties where better moisture remains in
place. Expect slightly cooler highs today with most areas in the
middle to upper 80s. Overnight lows Saturday will be slightly
cooler as well by a degree or two mostly in the middle 60s.


As of 300 AM Friday...Deep high pressure extending from the
surface up through 500 mb over the southern Great Lakes will
deflect the jet stream well north of the Carolinas this weekend.
An upper low developing across the FL/AL Gulf Coast have little
direct impact on our weather. It is interesting to note how
fortunate we are that Hurricane Maria is expected to move north
along 71-72 degrees west longitude this weekend, as a track
just a few degrees closer to Florida would likely get pulled
westward in between the two upper level systems -- much like
Hurricane Hugo did on this day back in 1989. The new 00Z ECMWF
shows Maria getting awfully close to that tipping point in the
steering flow...something that will need to be monitored

The surface pattern looks much like the upper pattern minus the
upper low along the Gulf Coast. Northeasterly flow between Maria
and the Great Lakes high will remain warm, but with dry out with
time as a subsidence inversion develops across the area. This
layer of warm air between 5000-7000 feet AGL will cap off any
daytime cumulus clouds and virtually guarantee dry weather both
Saturday and Sunday.

850 mb temps on Thursday were around +16C and should remain in
the +15C to +16C range both Saturday and Sunday. This should
provide highs 83-86 for the coastal counties and 86-89 inland.


As of 300 PM Thursday...A pleasant, seasonably warm and dry
extended forecast in the cards, provided no surprises arise in
the projected forecast track of Hurricane Maria, who is slated
to pass slowly north but well offshore of the Carolinas Monday
through Wednesday of next week. Aside from this, a pronounced
upper ridge will dominate the synoptic pattern, providing the
warm and mainly dry weather. Cross-sectional analysis through
time shows exceptionally dry mid-level air through the long
range period, keeping pop values very low, in the isolated to
none category. The exception will be very late or just beyond
the period next Friday, when a highly amplified upper trough
begins to drop SE toward the East coast. This will begin to
increase rain chances, while associated shear aloft begins to
guide Maria off to the NE away from the Mid-Atlantic coast.


As of 11Z...Some early morning fog exists in spots around the
eastern Carolinas. In particular there is fog at LBT where
visibilities have been as low as 3/4 mile recently. Morning sun
should quickly burn away this fog with VFR conditions
anticipated the rest of the day. Daytime cumulus should develop
this afternoon with bases around 5000 feet AGL. High pressure
over the Great Lakes will push drier air southwestward today and
tonight. This should keep any shower activity confined to
coastal South Carolina (including CRE and MYR) where the
afternoon seabreeze will bring some richer maritime moisture
onshore. VFR conditions this evening may decrease to MVFR/IFR
again late tonight in patchy ground fog.

Extended Outlook...Mainly VFR conditions through the period with
the exception of possible MVFR/IFR conditions due to low clouds
and fog each morning.


As of 300 AM Friday...Light winds fields will continue to prevail
across the coastal waters through the period. With weak high
pressure building in the direction through about midday will have a
northerly component. Once again the sea breeze will dictate things
this afternoon with southeast winds. Winds will turn back from the
north once again tonight. The bigger story is the long anticipated
swell from Maria is arriving. Significant seas this morning of 2-3
feet will increase by Saturday morning to 4-6 feet. Will go ahead
and issue what is expected to be an extended Small Craft

As of 300 AM Friday...1020 mb high pressure centered over the
southern Great Lakes will move very little this weekend. Weather
conditions will be increasingly influenced by Hurricane Maria
which is expected to move northward along 71-72 degrees west
longitude this weekend. Although Maria`s strong winds will
remain a couple of hundred miles east of the Carolina coastline,
increasing wave heights (long period swells) are expected to
create hazardous marine conditions all this weekend into early
next week. By Sunday night seas of 5-7 feet will be common
across the area, with wavelengths long enough to create shoaling
and large breaking waves along the length of Frying Pan Shoals.

As of 300 PM Thursday...Unfortunately for the marine community,
this period will pose treacherous wave conditions with
hazardous seas nearly a certainty as Maria approaches and passes
slowly north, but off the SC/NC coast. The slow movement north
will bring prolonged and dangerous marine conditions, as seas
build to 6-11 feet early next week, remaining elevated before a
more notable subsiding trend late next week. In addition to the
large waves, N winds will likely gusts to 25 KT early next week
as Maria passes slowly north well offshore. This will only throw
another layer of hazard on top of an existing one. The
energetic, fast moving long period energy will instigate
turbulence in area inlets during the outgoing tides, and will
produce larger than normal breakers near sand-bars while
expanding the width of the surf zone. This will require multiple
days of advisories, likely initiated by the weekend.


NC...Coastal Flood Advisory from 11 AM this morning to 1 PM EDT
     this afternoon for NCZ107.
MARINE...Small Craft Advisory from 2 AM Saturday to 6 PM EDT Monday for



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