Area Forecast Discussion
Issued by NWS Wilmington, NC

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234
FXUS62 KILM 211725
AFDILM

Area Forecast Discussion
National Weather Service Wilmington NC
125 PM EDT Mon Aug 21 2017

.SYNOPSIS...
A weak and stalled front will slowly dissipate to just a trof
of low pressure today. Moisture from an upper trof to our
south will make its way onshore and inland during today.
High pressure will expand across the area from the western
Atlantic late today thru early Wednesday, allowing the heat
and high humidity to continue. A modest cold front pushing
southeast will track across the Eastern Carolinas late
Wednesday night thru Thursday. Models indicate this front to
continue south and east of the area before stalling on Fri.
This will enable Canadian high pressure to build in behind
the front bringing drier weather and slightly below normal
temps for the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1030 AM Monday...Daytime heating has led to convective
clouds and a few showers thus far across inland areas. Some of
the convection associated with a persistent inverted surface
trough and mid level deformation has drifted onshore as well.
The latest NAM keeps most of the activity along the coast as
does a lot of other guidance. I will give it another hour or two
to monitor trends but a lowering of pops may be in order. The
cloud cover forecast is also looking a little better for eclipse
viewing although it will remain somewhat of a challenge,
especially along coastal areas. No other changes. Previous
discussion follows:


Isolated scattered showers offshore will
migrate towards shore through the early morning hours, and
potentially bring light precip amounts to the nearshore zones
in the predawn hours. Also anticipate very good potential for
fog to develop towards daybreak, given similar low-level
moisture profile as last couple of days, and even lighter winds
in the lowest few thousand feet. Abundant low-level moisture and
instability should allow for the development of widely
scattered showers and thunderstorms by midday, primarily along
the sea breeze and the remnants of frontal boundary lying across
the southern CWA. Convection will fade with the loss of heating
after sunset. High temps will range from the upper 80s coast to
the mid 90s across the Pee Dee, and this will lead to heat
indices topping out in the low 100s.

As far as sky cover for eclipse viewing, time-height cross
sections do indicate some mid-level dry air, however a blanket
of moisture around 200 mb will likely result in a filtered view
through thin cirrus at best. More than likely, any potential
glimpse would have to come between cumulus buildups, which are
expected to begin by late morning.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
As of 330 AM Monday...Western Atlantic ridging sfc and aloft
will dominate the FA`s weather Tue. Weak inverted mid-level
troffing extending from the Gulf of Mexico northeastward across
eastern Georgia and the eastern Carolinas. This troffing
apparently broke off from the upper low that pushed westward
across the Gulf of Mexico to near the TX and Mexico coast at the
start of the short term period. The dynamics associated with
this upper trof will combine with the sea breeze and a sfc trof,
which was once a stalled frontal boundary, and produce a round
of convection. Will indicate chance POPs but may need to be
upped especially with various model Mos Guidance not very
enthusiastic with shower and thunderstorm activity during Tue.
For Wednesday, the upper ridging associated with the Western
Atlantic High, is progged to get shunted southward as the upper
troffing amplifies and expands southward across the Eastern
1/3rd of the U.S. This will push a sfc cold front southeastward,
reaching the front doorsteps of the ILM CWA by Thu morning. Will
indicate increasing POPs during Wednesday and continuing that
trend thru Wed night with a POP peak in the high chance
category. Will need to monitor late Wed into Thu for possible
severe thunderstorm activity given the decent dynamics involved.
Daily max/min temps will remain slightly hier than the norm for
this time of the year, thus continuing with the heat and high
humidity.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 3 PM Sunday...Primary feature influencing extended
forecasts is cold frontal passage early Thursday. This is
supported by GFS/ECMWF upper patterns, both of which also
migrate Canadian High pressure into the region Friday through
the weekend, imparting a slightly drier and cooler feel than
late. GOES-16 shows the circulation near 20N north of Puerto
Rico, which may fester off the FL coast near a stalled
boundary early next week, potentially deepening. Regardless of
intensity, the expectation is this feature will lift to the
north slowly, remaining offshore of our coast. A few strong
storms are possible early Thursday as wind shear aloft and low-
level convergence increase as the upper trough edges in.

&&

.AVIATION /18Z MONDAY THROUGH FRIDAY/...
As of 18Z...Expect mostly VFR conditions for the afternoon and
evening hours. There is some convection around and coverage may
increase for a few hours but not enough confidence to put in other
than VCTS. Guidance is showing a good signal for fog area wide
Tuesday morning. I addressed with prevailing MVFR for this cycle but
some IFR could be in play as well.

Extended Outlook...Diurnal showers/tstms expected Wednesday
afternoon, becoming more numerous Wednesday night and Thursday
with fropa. Convective potential will decrease Friday as the
front moves south of the area.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
As of 1030 AM Monday...No changes to the coastal waters forecast
with the mid morning update. Previous discussion follows:


Isolated showers over the waters will
migrate northward through the predawn hours. Potential for
widely scattered showers and thunderstorms will continue over
the waters through the period, although they should be dampened
out a bit during the daytime hours once the sea breeze
circulation develops. Winds will remain light and variable in a
weak pressure field, with seas around 2 ft. Models continue to
show a 2 ft 9 second swell moving into the waters late tonight.

SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
As of 330 AM Monday...Winds and sea conditions will start out
somewhat benign given the relaxed sfc pg and a weak sfc
pressure pattern. This will change by late Tue thru the
remainder of this period. The sfc pg will begin to tighten along
with an organizing sfc pressure pattern that will both yield
increasing SW winds. The significant seas will initially be
driven by an ESE-SE 1 to 2 foot ground swell at 10 second
periods initially, that will build to 2 to possibly 3 feet late
Tue thru much of Wed. This ground swell will dominate the seas
spectrum thruout this period with wind waves helping to push
significant seas to a 2 to 4 foot range during Wed. Will need to
be cognizant of any convection that pushes off the NC and SC
mainlands this period, and especially late this period when
thunderstorm activity becomes better organized and potentially
stronger.

LONG TERM /THURSDAY THROUGH FRIDAY/...
As of 300 PM Sunday...The extended marine period will become a
bit bumpy ahead and after a cold frontal passage on Thursday.
A wind shift will migrate across the 0- 20 NM waters early
Thursday. Strong Canadian high pressure will interact with the
front offshore to produce NE winds 15-20 KT Thursday into
Friday. As a result, `Caution` and even `Advisory` headlines are
possible this period. Seas of 3-5 feet can be expected
Wednesday afternoon through much of Friday before subsiding, and
up to 6 feet well offshore. A few storms may be strong
Wednesday night through Thursday as a cold front crosses the
waters and radar updates are encouraged.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...None.
NC...None.
MARINE...None.

&&

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



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