Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 230529
AFDILM

Area Forecast Discussion
National Weather Service Wilmington NC
129 AM EDT Wed May 23 2018

.SYNOPSIS...
A tropical airmass will remain across the Carolinas for the next
week. A cold front approaching from the north will become a
focus for better chances of showers or thunderstorms during
Wednesday and Thursday. The front will dissipate Friday, with
fewer showers expected into Saturday. Low pressure developing
this weekend across the Gulf of Mexico will throw more moisture
our way for Sunday and Monday, with substantial rain chances
returning to the area.

&&

.NEAR TERM /THROUGH TODAY/...
As of 830 PM Tuesday...Diurnally driven convection has ended
across the ILM CWA. The 88D echoes over the adjacent Atlantic
waters are for the most part chaff. Will update to remove POPs
for the rest of this evening. Based on latest Sat imagery
trends, have improved sky conditions by cutting back on the
clouds for the remainder of this evening and into the pre-dawn
Wed hrs. This could set up a night for patchy to possibly areas
of fog if the sfc winds are able to decouple. Local PWS at 1.2
this morning will rise to around 1.7 Wed morning. During the
pre-dawn Wed hrs, have indicated a low chance POP, mainly along
the immediate coast and waters and stretching inland by 25
miles. This the result of a weak system traversing northeast
across the coastal area as it tracks northeastward...reaching
the NE portions of the CWA around daybreak Wed. Have
tweaked the hrly temps/dewpts and tonights lows, but with no
categorical changes.

Previous......................................................
As of 300 PM Tuesday...The convection that developed along
the sea- breeze just before noon is now decreasing in coverage.
Inland isolated convection appears to continue as the HRRR 16
UTC is not showing an increase activity this evening. So will
continue with isolated showers and thunderstorm through the
evening.

At the surface the area will continue to be on the eastern
edge of the Bermuda high and the deeper moisture is seen
returning with precipitable water near 2 inches. Both the NAM
and GFS are showing diurnal convection with the GFS being a bit
more zealous with convection in the northwest quarter of the
area. The NAM is showing less precipitation mainly west of the
sea- breeze and focused over northeast South Carolina. The 12
UTC ECMWF is closer to the NAM12 solution.

Lows tonight will range from the upper 60s inland to the
lower 70s at the coast. Highs on Wednesday will be in the
middle 80s inland and the lower 80s at the coast.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/...
As of 300 PM Tuesday...The chance for showers and
thunderstorms will increase Wednesday night into Thursday as a
cold front drifts south across the forecast area. The
precipitable water will pool ahead and along the boundary along
with marginal to moderate surface based instability. While the
amount of cloud cover will ultimately impact the amount of
instability any increase in cloud cover would also imply
slightly cooler temperatures than what is currently forecast.
For now favor a blend of MAV/MET temperatures, and POPs
decreasing Thursday evening with the front drifting farther
south and dissipating.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
As of 300 PM Tuesday...A baggy upper level trough across the
lower Mississippi Valley and Gulf of Mexico will become better
defined Saturday and Sunday. Upper ridges building across the
Pacific coast of Mexico and out over the western Atlantic
between the Bahamas and Bermuda will help to spin this feature
up. A surge of Caribbean moisture very similar to what we saw
last weekend will be drawn northward in the deep southerly flow
between this upper trough and the offshore ridge, and this
could lead to another good rainfall event Sunday into Monday.
The latest WPC QPF outlook for just Sunday and Monday is around
1.5 inches across our area, with forecast 7-day totals of 2-3
inches.

Latest models show there will probably be some sort of low
pressure development across the Gulf of Mexico late this week,
but FSU cyclone phase diagrams show only the Canadian
developing a significant warm core aloft. The 12z ECMWF (not
currently part of the FSU website) shows the cyclone keeping a
pronounced gradient in 1000-500 mb thickness above the surface
low, implying subtropical characteristics at best. The GFS is
the farthest east with its low pressure development across
Florida on Sunday, while other guidance is westward. While not
ruling out anything just yet, it`s expected the low will remain
too far west for any direct impacts on the Carolinas, but
enhanced southerly flow should help enhance our rainfall
potential Sunday and Monday when my highest rainfall chances
(50-70 percent) are currently forecast.

The warmest days should be Friday and Saturday when there will
be more sunshine and lower shower chances. Highs should reach
the mid to upper 80s both days inland, several degrees cooler
near the coast. Temperatures should top out in the lower 80s
Sunday, and lower to mid 80s Monday and Tuesday. Lows in the
upper 60s to lower 70s through the period are evidence of the
tropical airmass we`ll have in place.

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
As of 06Z...Local radar is mostly quiet this morning and is
expected to remain so until later in the day when heating
commences. Overall expect a similar morning to yesterday with
some tempo MVFR BR developing within overall VFR conditions.
Good coverage of showers and thunderstorms expected later today
but confidence is not quite high enough to warrant anything
other than VCTS. The 12 and certainly 18 Z package may have
just enough confidence on near term trends to better pinpoint.

Extended Outlook...The potential for MVFR/tempo IFR will
increase late Wed/Thur as a cold front drops across the area
and again during the weekend as tropical moisture returns.

&&

.MARINE...
NEAR TERM /THROUGH WEDNESDAY/...
As of 845 PM Tuesday...Latest 88D echoes over the local waters
are NOT showers or thunderstorms, they mimic aluminum chaff
used by the military to evade radar tracking. Do think, showers
and convection will occur, mainly during the pre-dawn Wed hrs as
a weak system moves northeast along the immediate coast.

The sfc ridge axis from Bermuda high pressure, will continue to
extend west and onshore. This onshore placement is now south of
the local waters. This has resulted with mainly a SW direction
for all waters. The sfc pg will be conducive to around 10 kt or
10-15 kt wind speeds. Significant seas will run around 3 ft and
will primarily be influenced by the SE ground swell that has
shown some degradation during the past 12 hrs.

Previous...................................................
As of 300 PM Tuesday...The marine waters will continue to be
under the influence of the high pressure we have seen the last
few days. Winds will be southwest overnight and will shift to
the south on Wednesday as the sea-breeze develops. Winds will be
around 10 knots increasing to 10 to 15 knots during Wednesday.
Seas will range between 2 and 3 feet through the period.

SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/...
As of 300 PM Tuesday...Bermuda high pressure will maintain
southwesterly flow across the waters Wednesday evening. However,
the flow will veer to a westerly direction as a weak front
drifts south across the area. The front is expected to become
increasingly diffuse as it passes south of the waters allowing
weak onshore flow to prevail by Thursday afternoon. Seas will
be 3 ft or less through the period. Scattered showers and
thunderstorms are also possible with the front in the vicinity.

LONG TERM /FRIDAY THROUGH SUNDAY/...
As of 300 PM Tuesday...Bermuda high pressure will remain well
off the Southeast coast this weekend. By itself it would provide
a gentle southerly wind and typical summertime weather. However
models over the past few days have been showing the potential
for a tropical or subtropical cyclone to develop across the
Gulf of Mexico Friday or Saturday. The GFS is the farthest east
of any model with its latest run showing a low reaching Florida
on Sunday, while the ECMWF and Canadian are farther west. While
it`s too early to completely rule out impacts, our latest
forecast has south winds increasing to around 15 kt Sunday, with
a lengthening fetch of stronger winds extending down into the
Bahamas. This could build seas up toward 6 feet, assuming our
wind forecast is correct.

&&

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

&&

$$
SYNOPSIS...TRA
NEAR TERM...DCH/DRH
SHORT TERM...SRP
LONG TERM...TRA
AVIATION...SHK
MARINE...


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