Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 212355

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

High pressure will expand across the area from the western
Atlantic through Wednesday, allowing the heat and high humidity
to continue. A cold front will track across the Eastern
Carolinas from the northwest late Wednesday night thru Thursday.
Canadian high pressure will build in behind the front bringing
drier and breezier weather with slightly below normal
temperatures for the weekend.


As of 8 PM Monday...A few spot showers are gradually fading with
the sunset. Expect a dry overnight period with fog developing
after midnight. Only minor tweaks made to the forecast with the
latest update. Previous discussion follows:

Although the area is primarily under the influence of mid level
ridging, there is a slight deformation zone and surface
troughing residing offshore that is sparking convection. This
will continue through the afternoon hours and subside this
evening. There may be another diurnal increase over the waters.
The same elements will be in play Tuesday although with moisture
profiles a little drier, the coverage should be less. No
surprises in temperatures with another night of lower to middle
70s and highs Tuesday from the upper 80s along the coast to
lower 90s inland.


As of 300 PM Monday...Mid to upper level ridge will be sprawled
south and east of forecast area Tues night into Wed. A bit of
shortwave energy riding up around the ridge from the south will
act to enhance localized convection along Piedmont trough and
sea breeze front into Tues eve. The westerly steering flow will
push any debris clouds or storms toward the coast in the
evening. Expect a lull through the night into early Wed, but a
cold front will reach into the Carolinas on Wed and expect
trough to push east and any convection once again to move toward
the coast in a westerly push. Convective activity ahead of the
front will increase into Wed evening as mid to upper trough digs
down from the north pushing the front east. Plenty of warm air
and moisture ahead of the front combined with dynamics aloft
could lead to stronger storms into late Wed and Wed night as
front marches east. Expect boundary to be right near I-95
corridor by Thurs at daybreak. Temps will be in the 70s
overnight and 90 to 94 most places Wed aftn. Head index values
will reach around 100 degrees in a continued hot and humid air


As of 300 PM Monday...The extended period is initiated with a
frontal boundary along the coast, pushed offshore by Canadian
high pressure by Thursday night. The seasonably strong Canadian
anticyclone will continue to press SSE into the area through the
weekend, offering a dose of a very early fall feel here with
slight cooling and drying. As the strong high interacts with low
pressure development off Florida, a stiff NE flow should
prevail much of this period into early next week. This will keep
maximums moderated, and notably milder minimums at and near the
coast compared to the interior. Highest POp values is the very
beginning of the extended on Thursday, while low temperatures
this weekend dip into the 60s in many locations inland. Because
of upper winds, any tropical formation off Florida this weekend
should remain east and offshore of the Carolinas through early
next week.


As of 00Z...Other than the very isolated spot shower,
convection has ended for the evening. Good confidence VFR all
terminals through midnight or a couple hours beyond that.
Moderate confidence all terminals will experience periods of IFR
restrictions for vsby in fog in the early morning hours of
Tuesday. Isolated to scattered convection will likely develop
Tuesday afternoon.

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


As of 8 PM Monday...Latest obs show SE winds of 5 to 10 kts with
only 2 ft of seas. This fits in well with the forecast as issued
this afternoon. No changes were made with the latest update.
Previous discussion follows:

Conditions will remain quiet across the coastal waters with
very little in the way of forcing for the wind fields. Expect an
east to southeast flow of ten knots or less tonight through
Tuesday. There are some indications of slightly stronger winds
(10-15 knots) late in the period. Significant seas will continue
to hover around two feet.

As of 300 PM Monday...Winds will increase into Tues eve up 10
to 15 kts as gradient tightens between high pressure to the east
and trough to the west. Winds will lighten toward daybreak Wed
but will increase again with an approach of a cold front Wed
night into early Thurs. Expect seas to reach up near 4 ft in
outer waters Tues eve with a slight drop Wed morning and rise
again Wed night. Overall expect 2 to 4 ft seas with a longer
period, up to 10 sec, SE swell mixing with the shorter period
wind waves.

As of 300 PM Monday...This period will become fraught with
challenges for marine activities as a seasonably strong Canadian
high forces a cold front across the coast Thursday. Aside from
TSTMS Thursday on the 0-20 NM waters, NE winds will begin to
increase Thursday night and Friday as the Canadian high presses
SSE over the waters, and a Small Craft Advisory may be needed
for 25 KT gusts and 6 foot seas offshore. The strong onshore
flow will likely persist into Saturday, as the high interacts
with deepening low pressure off Florida, and thus maintaining
rough conditions into the weekend.





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