Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 261414
AFDILM

Area Forecast Discussion
National Weather Service Wilmington NC
1014 AM EDT Tue Sep 26 2017

.SYNOPSIS...
Hazardous beach conditions will continue as hurricane Maria
moves slowly north offshore of the Carolinas. Maria will
accelerate away from the United States beginning Thursday.
A cold front passage late Thursday will bring cooler and drier
air into the Carolinas Friday into this weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1015 AM Tuesday...Forecast is in good shape with only
minor tweaks needed. The main challenge will be the erosion of
the stratus layer later this afternoon and evening. Previous
discussion follows:

Northward moving Hurricane Maria will slowly
pass well east of the area today, moving northeast of the area
tonight. Breezy northerly winds will become northwest later today
and into tonight. Moisture below 500 mb remains high through the
period as Maria`s circulation continues to spread an abundance of
tropical moisture over the region. Downward motion due to mid-level
subsidence on the periphery of the storm will work to offset what
little diurnal instability develops. Low level cloud cover will
limit heating today, keeping highs in the upper 70s to lower 80s in
most areas. Across inland SC there may be a little less cloud cover,
allowing for slightly more insolation (and marginally warmer temps).
There will be a little less subsidence across inland SC but also a
little less moisture. Cannot rule out an isolated shower but the
best shot at measurable rainfall during the period looks to be
across southeastern NC. Light showers and/or sprinkles will be
possible through early evening with mid to late afternoon favored.
By early evening the best low level convergence shifts north and
diurnal instability decreases. Do not expect a lot of precipitation
both in coverage or amount, but brief showers/sprinkles certainly
remain possible. Clouds will linger overnight and, combined with
strong boundary layer mixing, will help keep lows well above
climo.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
As of 300 PM Monday...By daybreak on Wednesday, Maria will be
positioned roughly 150 miles east of Cape Hatteras, meandering
there into Thursday, before an acceleration eastward Thursday
night. This progression will open the door for cold frontal
passage late Thursday night and early Friday, bringing a change
in air mass Friday into the weekend. This will result in temps
more indicative climate-wise for late September, after an above
normal temp regime this week. This will be a dry cold front as
moisture aloft remains in limited supply, and subsidence aloft
will be formidable in N-NW flow. Downslope flow prior to the
cold frontal passage will result in exceptionally warm temps,
and while 95 degrees will be a difficult record to break at ILM
on Wednesday, the 91 on Thursday set back in 1998 could be
closely approached.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
As of 300 PM Monday...Subsidence in the wake of Maria and pre-
frontal warming will lead to one more day of above-average
temperatures before a cooling trend commences. A consensus of
guidance gives us highs of around 90 on Thursday. A cold front
will move offshore later on Thursday, bringing us near to well-
below normal temperatures by Friday, with cool weather
continuing into the weekend. The cold front will come through
dry, although isolated to widely scattered showers are possible
along the coast Friday night into Saturday as a strong upper
disturbance dips SE across the mid-Atlantic states.

&&

.AVIATION /14Z TUESDAY THROUGH SATURDAY/...
As of 10Z...Forecast soundings and cross section suggest low
stratus deck with all terminals potentially affected with IFR
ceilings, best chances at NC sites. IFR ceilings will hang
around through mid morning before lifting to MVFR for much of
the day, except for FLO which should quickly pop up to VFR. Low
chance ILM could see brief shower or drizzle but if this were to
happen duration would be very brief. Clearing will start to
develop over inland SC prior to sunset and gradually spread east
and north overnight. High cloud may linger beyond the end of
the period closer to the coast but low stratus seems less likely
given forecast moisture profiles. Boundary layer winds should
prevent any fog. Similar set up 12z-18z Wed but SC may remain
VFR as Maria pulls farther north.

Winds from the north this morning will gradually back to
northwest during the day. Speeds at the coastal terminals could
gust to 18 to 22 kt later this morning into late afternoon or
early evening before speeds start to drop off.

Extended Outlook...MVFR ceilings may linger/redevelop at the
coastal terminals Wed night, mainly KILM. Wind gusts at KILM
may gust to 15 to 20 kt.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
As of 1015 AM Tuesday...No changes to the coastal waters
forecast this morning. Rugged condtions continue. Previous
discussion follows:

Gusty northerly winds this morning will gradually back to
northwest as Hurricane Maria passes well east of the area. SCA
headline continues for all zones, mainly due to swells from the
storm. In addition, wind speeds across NC waters will remain in
the 20-25 kt range through the end of the period. Later today
and tonight Maria will be northeast of the area and in the
process of moving away from the waters. Despite this, swells
above SCA thresholds will likely continue through the end of the
period. Nearshore SC waters may start to see seas dropping
below 6 ft later tonight but the majority of the waters will
remain in the 6 to 10 ft range with potential for up to 15 ft
across NC zones near 20 nm. NO TSTMS over the 0-20 NM waters
this period but a few brief showers possible Wednesday north of
Figure 8 island is possible.

SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
As of 3 AM Tuesday...SCA in large seas and NW winds 20-25 KT
starts Wednesday off rough, but into Thursday vast improvement
is expected as Maria not only weakens but begins to accelerate
away from the East Coast. Sea height recovery will require an
SCA likely all of Wednesday before headlines are likely dropped
sometime Thursday. N-NW winds will prevail all of this period
although the wave-height trend is a subsiding one. Seas 5-9 feet
Wednesday will drop to 3-5 feet during the day Thursday in
fading E swell, diminishing NW wind-seas, and easing NE fresh
swell or `mature wind-seas`. A myriad of wave trains in the mix
but overall heights dropping in each of the partitioned waves.

LONG TERM /THURSDAY THROUGH SATURDAY/...
As of 3 PM Monday...Expect gradually improving conditions over
the waters as Maria moves well northeast into the central
Atlantic and a weak pressure gradient takes its place. Do not
expect any warnings or advisories during the long term. Highest
winds and seas will be on Thursday for our NC coastal waters,
with 10 to 15 kt winds and 3 to 5 ft seas. These conditions will
improve, with seas in the 2 to 4 ft range and winds of only
around 10 kts throughout by evening.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...High Rip Current Risk until 9 PM EDT this evening for SCZ054-
     056.
NC...High Rip Current Risk until 9 PM EDT this evening for NCZ106-
     108-110.
MARINE...Small Craft Advisory until 8 PM EDT Wednesday for AMZ250-252-
     254-256.

&&

$$
SYNOPSIS...
NEAR TERM...III/SHK
SHORT TERM...MJC
LONG TERM...REK
AVIATION...MJC
MARINE...


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