Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 230155
AFDILM

Area Forecast Discussion
National Weather Service Wilmington NC
955 PM EDT Fri Sep 22 2017

.SYNOPSIS...
Building high pressure aloft and at the surface will bring dry
but warm air across the Carolinas this weekend and well into the
upcoming work week. Hurricane Maria is expected to remain well
offshore from the forecast area as she passes bye during the
upcoming work week. However, she will provide the coastal areas
with increasing long period swell that will result in strong
rip currents and large surf along the area beaches, as well as
hazardous marine conditions especially when venturing thru area
inlets to and from the Atlantic Ocean.

&&

.NEAR TERM /THROUGH SATURDAY/...
As of 915 PM Friday...Diurnal cu has basically scoured out with
only leftover debris clouds from the earlier isolated showers
left. And this too will dissipate. Did not hit the fog as hard
tonight when compared to last night. Having been much drier
today along with convection isolated. Still moisture avbl below
850mb for Cu to pop back up come Sat mid to late morning.
However, as far as the overnight, mainly SKC with thin Ci
pushing across the FA later tonight and Sat. This blowoff Ci is
from the ongoing convection off the Florida and Georgia coasts
unrelated to Hurricane Maria. With winds decoupling across the
FA, even along the coast, patchy shallow ground fog will occur.
In addition, decent radiational cooling will occur with some
sites dropping into the 60-65 range, especially with nights now
as long as days this autumnal equinox, and will only get longer
as we progress thru the calender to the Winter Solstice.

Previous......................................................
As of 300 PM Friday...Since convection is struggling through
the window of maximum insolation, diurnal cooling with our
lowering ball of fire will put the curtail on convection into
the late afternoon to early evening, leaving a clear sky tonight
as the cumulus dissolves into the evening sky. Under clear
skies and decelerating winds, patches of fog can be expected
between 4am and 8am. Minimums will settle to 65-68 across most
locals and low 70s near the beaches and ICW. The surfzone and
area beaches will begin to possess a hazard as long period SE
swell from distant Marie intensifies rip currents, while
creating large and powerful breakers near shore. This will pose
a threat to surf- waders, and even small children or elderly not
in the water but standing by the oceans roar, where wave run-up
can be speedy and strong, as wave periods will be on the order
of 15 seconds, representing a high translational velocity into
the surfzone. It is beyond this period however, namely Sunday,
that the surf becomes large. For Saturday 4-7 ft breakers, and a
`high- risk` of rip currents along all beaches.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
As of 300 PM Friday...Although the weather will remain quiet,
the seas and surf will not. The main impact this weekend will
come from high surf and strong rip currents at the beaches.

Otherwise, Jose will continue to churn in the northern Atlantic
and Maria will continue its trek northward, while high pressure
moves slowly east across the Great Lakes. The Carolinas will
basically be under the influence of high pressure in the
northeasterly flow between these systems. A weaker gradient
flow initially will allow the sea breeze to dominate closer to
the coast helping to produce a greater on shore flow Sat eve.
The pcp water values will be near 1.3 inches closer to the coast
and down near an inch in a drier NE flow Sat eve, but a boundary
from Jose will shift south overnight Sat into early Sun. This
will produce some clouds and perhaps a spotty shower over the
waters. Otherwise expect mainly clear to partly cloudy skies and
overnight lows in the mid 60s most places.

The winds will pick up on Sun as gradient tightens with
northerly movement of Maria which should reach about 500 to 600
miles to the southeast, but coastal Carolinas will remain in dry
air and subsidence as ridge builds down over the area aloft and
we remain on back side of extreme outer periphery of Maria. H5
heights will be up near 588 dm with 850 temps up near 16 to 17c.
This will help to keep a dry forecast with warm temps up in the
mid 80s for Sunday. Models show a some drier air advecting in
overnight Sunday with slightly lower dewpoints which may shave a
couple of degrees off overnight low, but still expected in the
mid 60s.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
As of 300 PM Friday...Hurricane Maria will be slowly making its
way north well off the coast of the Carolinas through the first
half of the week. Expected impacts will be dangerous surf and
an elevated rip current risk from long period (15 sec) swells.
This swell energy will translate into breaking waves as high as
10 to 15 feet along the beaches of New Hanover and Pender
counties, and 6 to 10 feet along the beaches of Brunswick, Horry
and Georgetown counties into Wednesday. The swell energy should
begin to ease late Wednesday, but dangerous surf and an
elevated rip current risk will likely continue into Friday.

Northeast to north winds will be breezy along the coast, and
gust occasionally into the 20-30 mph range by Tuesday-
Wednesday. It will be a tough call at this point to determine
how much peripheral moisture from Maria will affect the area,
however it is reasonable to expect for the ILM CWA, that SE NC
will have the best chance for precipitation based on the current
forecast track of Maria. The highest PoPs, which will still
remain less than 30% at this time, will be Tuesday into
Wednesday, before the cyclone gets picked up by the westerlies
on Thursday as indicated by both the GFS and ECMWF.

Upper level ridging and subsidence west of the hurricane will
likely result in a sharp sky cover gradient and temperatures
remaining a few degrees above normal through the week.

&&

.AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...
As of 00Z...VFR conditions thruout this fcst period except
during the 06Z-12Z time frame where MVFR and/or IFR conditions
may result due to fog. Not much pcpn fell today as compared to
yesterday at this time. As a result, will not hit the fog as
hard eventhough most terminals will see winds decoupling quickly
this evening and remaining calm thruout the overnight. For
Saturday, diurnally driven Cu at 4k to 5k feet will be fcst but
will keep scattered in coverage. SCT to BKN thin Cirrus will
creep northward from the convection off the Florida and Georgia
coasts overnight thru Sat. Northeast winds around 5 kt Sat
daytime morning will veer to the E-SE at 5 to 10 kt across the
coastal terminals due to a resultant wind, aka the sea breeze.
This will also push the Cu inland leaving thin Cirrus overhead.

Extended Outlook...Mainly VFR conditions through the period with
the exception of possible MVFR/IFR conditions due to low clouds
and fog each morning, mainly between 08z-12z.

&&

.MARINE...
NEAR TERM /THROUGH SATURDAY/...
As of 930 PM Friday...Small Craft advisory, mainly for
significant seas, commences at 6 AM Saturday.

A relaxed sfc pressure gradient will result in wind speeds 10
kt or less tonight thru Saturday. The progged sfc pressure
pattern will yield a ENE-E wind direction tonight thru Sat.
Significant seas will build tonight thru Sat and beyond,
reaching SCA thresholds during Saturday. Hurricane Maria`s
swell from the SE, will be the primary input to the significant
seas thruout the near term and beyond. Periods will range
between 13 to as much as 17 seconds. This long period swell,
combined with an outgoing tide, will begin to make navigating
to and from the Atlantic dangerous and downright hazardous as
Maria`s swell builds.

Previous...................................................
As of 300 PM Friday...Although N through ENE winds this period
will not be strong, increasing SE swell from Maria has prompted
a `hazardous seas` advisory, effective from 6 AM Saturday
through at least early next week, likely into mid-week, since
Maria will slow down once offshore of the Carolinas. 4-7 foot SE
waves every 15 seconds will produce turbulence and standing
waves in area inlets during the outgoing tides, while increasing
the width of the surfzone of tumultuous breakers. No TSTMS are
expected through Saturday over the 0-20 NM waters. Onshore winds
can be expected Saturday with high pressure to the north and
Maria east of the Bahamas.

SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
As of 300 PM Friday...High pressure will extend down from the
Great Lakes this weekend as Jose continues to spin in the North
Atlantic and Maria treks north from north of the
Bahamas. A general northeasterly flow will increase heading
into Sunday up to 15 to 20 kts in the outer waters, but
otherwise winds will be in the 5 to 10 kt range. A very long
period swell up to 11 to 15 seconds will continue through the
weekend. An increasing northeast shorter period wind swell will
combine with this longer period swell to produce an increase in
seas from near 6 to 7 ft in outer waters Sat eve up to 10 to 12
ft Sun night into Monday. Expect shoaling and large breaking
waves along the length of Frying Pan Shoals. A small craft
advisory for hazardous seas mainly due to long period swells
will continue through the period.

LONG TERM /MONDAY THROUGH WEDNESDAY/...
As of 300 PM Friday...Long period southeasterly swells will be
ongoing Monday, ranging from as high as 8 to 10 feet every 15
seconds in the outer waters (15-20 nm). South of Cape Fear,
these are likely to decay to 4 to 6 feet as they approach the
coast, but north of Cape Fear, 6 to 8 footers will push in
closer. Based on the latest forecast track for Maria, northerly
winds will peak Tuesday night into Wednesday, with 20 to 25
knots north of Cape Fear. South of Cape Fear, a 15 to 20 knot
range can be expected. Expect Small Craft Advisory conditions
through the entire period.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...High Rip Current Risk from 7 AM EDT Saturday through Saturday
     evening for SCZ054-056.
NC...High Rip Current Risk from 7 AM EDT Saturday through Saturday
     evening for NCZ106-108-110.
MARINE...Small Craft Advisory for hazardous seas from 6 AM Saturday to
     6 AM EDT Tuesday for AMZ250-252-254-256.

&&

$$
SYNOPSIS...DCH
NEAR TERM...DCH/MJC
SHORT TERM...RGZ
LONG TERM...CRM
AVIATION...DCH


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