Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 160525
AFDILM

Area Forecast Discussion
National Weather Service Wilmington NC
125 AM EDT Wed Aug 16 2017

.SYNOPSIS...
Summertime heat and humidity will build and should peak through
Friday. Although showers and thunderstorms will gradually
become fewer in number, heat index values will climb, and heat
advisories may be needed Friday. Showers and thunderstorms will
increase during the weekend as a cold front approaches from the
north. This front will stall and dissipate nearby early next
week.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
As of 730 PM Tuesday...Latest radar loops show a cluster of
weak to moderate thunderstorms about to impact the Cape Fear
region, a few spot showers elsewhere. Will tweak forecast
slightly regarding timing of these features with the next
update, otherwise no major changes anticipated. Previous
discussion follows:

A sea breeze is resulting in isolated showers thus far while a
weak trough farther west and northwest has also resulted in some
convection as well. HRRR is supportive of widely scattered
storms through the afternoon, and into the evening as a weak
impulse moves across NC. Plan on carry chance POPs as a result
with little if any chances during the early morning hours. The
weak trough will be along the coast during Wednesday and with
moderate instability and precipitable water values >2.2 inches
will maintain chance POPs. Heat/humidity issues will be a
concern Wednesday with heat indices close to advisory thresholds
each day. Low temperatures tonight will be a category or two
above normal, which has been quite common through a bulk of this
summer.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH THURSDAY NIGHT/...
As of 3 PM Tuesday...Low amplitude mid-level ridge axis will slowly
transition eastward from eastern TN Wednesday night, across the
Appalachians Thursday, to the near or just off the coast by 12Z
Friday. Precipitable water values look to dip just below 2 inches
Wednesday night as northwest flow aloft ushers in a bit of modestly
drier air behind a decaying frontal boundary, but will return to
around 2.25 inches Thursday and Thursday night. Convection should
remain scattered in nature under the flat ridge, with sea breeze and
Piedmont trough acting as focusing mechanisms. Heat indices on
Thursday are expected to reach into a 100-105 range. Low temps each
night will dip into a 75-79 range.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
As of 300 PM Tuesday...Concern for the extended involves heat and
humidity Fri/Sat, followed by a cold front for the weekend and into
early next week.

Vertically stacked high pressure offshore will strengthen into
Saturday ahead of a shortwave and associated cold front dropping
into the OH VLY. This drives very warm air with high humidity into
the region, and highs Fri will climb into the 90s, with mid 90s
well inland, which combined with the high humidity will create near
heat-advisory apparent temperatures. Isolated showers and tstms are
possible Friday as well, but ridging aloft combined with lack of
significant forcing will keep coverage isolated. On Saturday, the
front will drop into the area and then likely stall as the shortwave
hangs back, the front becomes flow-parallel, and ridging persists to
the east. Convection chances will ramp up significantly Saturday,
with still good chances Sunday as the shortwave digs through the Mid-
Atlantic and offshore. Temps for the wknd will remain above climo as
well.

Concern then shifts to Monday, the day of the total solar eclipse.
Guidance has backed off on a clean FROPA, and has the front
dissipating overhead during Monday. This is much more typical for
late August. While this could create more clouds and unsettled
conditions for Monday across the area, mid-level flow does become
W/NW behind the aforementioned shortwave which brings some drier
air into the mid-levels. At this time a fairly typical August day is
expected with aftn CU and convection, especially focused along the
stalled boundary wherever that may set up. This does not suggest the
eclipse will not be visible, but may be temporarily blocked by
convection at times.

On Tuesday offshore high pressure re-asserts itself, but yet another
weak cold front will approach from the NW creating good convection
chances with continuing above climo heat and humidity.

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
As of 06Z...Most of the earlier convection has moved out of the
area. With synoptic conditions similar to last night, expect
inland fog to form in short order. The most favored location is
Lumberton where lighter wind fields reside and IFR is likely.
For Florence 850MB winds are a little stronger and I have
employed MVFR conditions. Later today expect isolated to
scattered convecton.

Extended Outlook...A brief period of MVFR or lower conditions
can not be ruled out in isolated to scattered showers and
thunderstorms through Fri. The risk for flight restrictions due
to showers and thunderstorms will increase on Sat. Low stratus
and some fog during the overnight and early morning hours may
result in flight restrictions as well each day.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
As of 730 PM Tuesday...Latest obs continue to show the influence
of far-distant Hurricane Gert, with a 3 to 4 ft easterly swell
with SW winds of only 10 to 15 kts. Forecast in good shape with
no changes planned. Previous discussion follows:

Swells from Gert will continue tonight but they will gradually
weaken. Seas will be 3-4 ft through tonight, primarily in an E
swell, and 3 ft or less during Wednesday. S-SW winds today will
veer to an offshore direction overnight as a weak trough moves
into the vicinity. Light southerly flow will develop again
during Wednesday once the sea breeze becomes established.

SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/...
As of 3 PM Tuesday...A decaying front across the waters Wednesday
night will result in light but potentially variable winds, along
with the possibility of scattered showers and thunderstorms. Latest
guidance suggests the boundary may shift just south of the waters
Wednesday night, allowing a period of NE winds before it washes out
Thursday morning. Wind direction will veer to the SE Thursday
afternoon, and SW Thursday night and Friday as a Piedmont trough and
Bermuda high reestablish.

LONG TERM /FRIDAY THROUGH SUNDAY/...
As of 300 PM Tuesday...A cold front approaching from the NW will
sandwich the waters with a pinched gradient as high pressure spins
offshore. This will drive increasing SW winds, increasing to around
15 kts by mid-Friday and persisting at these speeds into Sunday
morning. This front will stall and begin to dissipate inland from
the waters on Sunday, causing the gradient to relax and wind speeds
to fall to around 10 kts while maintaining a SW direction. Initially
seas will be just around 2 ft, but will increase steadily thanks to
an amplifying SW wind wave, becoming 3-5 ft by Saturday night.
Conditions should remain just below any cautionary statements
however. As the winds begin to ease Sunday, seas will follow, with
wave heights falling to around 3 ft at the end of the period.

&&

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

&&

$$
SYNOPSIS...JDW
NEAR TERM...REK/SRP
SHORT TERM...CRM
LONG TERM...JDW
AVIATION...SHK



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