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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KILM 221519
AFDILM

Area Forecast Discussion
National Weather Service Wilmington NC
1119 AM EDT Fri Sep 22 2017

.SYNOPSIS...
A weak disturbance aloft will drift to the southwest today and
tonight, producing isolated showers and thunderstorms mainly
this afternoon. Building high pressure aloft from the north
will bring dry but warm air across the Carolinas this 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, as well as hazardous
marine conditions offshore.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 10 AM Friday...A few adjustments to lower POP values and
sky cover in the early going and render afternoon coverage to
the isolated category, as recent model trends suppress farther
SW an h7-h5 cool pool. Before this happens however, diurnal
heating should trip off a few showers or a storm during the
early and middle afternoon, perhaps lingering into early evening
over SC. No other significant changes were made.

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.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
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
closely.

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.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
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.

&&

.AVIATION /15Z FRIDAY THROUGH TUESDAY/...
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.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
As of 1120 AM Friday...Converted small craft advisory for winds
and seas to just a hazardous seas advisory as seas will exceed
6 ft long before SCA winds arrive, no other changes. Long period
SE swell, or the fore-runners of distant Maria is fanning
ashore although of low amplitude for now, but this will change
as swell heights build.

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 Advisory.

SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
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.

LONG TERM /MONDAY THROUGH TUESDAY/...
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.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...None.
NC...Coastal Flood Advisory until 1 PM EDT this afternoon for
     NCZ107.
MARINE...Small Craft Advisory for hazardous seas from 6 AM Saturday to
     6 AM EDT Tuesday for AMZ250-252-254-256.

&&

$$

SYNOPSIS...MJC
NEAR TERM...SHK/MJC
SHORT TERM...TRA
LONG TERM...MJC
AVIATION...TRA