Small Craft Advisory 36, NWS Wilmington, NC

Area Forecast Discussion
National Weather Service Wilmington NC
337 AM EDT Sun May 27 2018

.SYNOPSIS...
Bermuda high pressure will provide warm and humid weather today
with isolated showers and thunderstorms becoming numerous this
evening. Moisture surging northward from Alberto, will lead to
periods of heavy rain late tonight and during Monday and this
may result in flooding in some areas. Scattered to numerous
showers and thunderstorms are expected Tuesday through Thursday
with perhaps less in the way of wet weather late in the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 300 AM Sunday...The Bermuda High will shift away from
the area through tonight as Subtropical Storm Alberto moves
slowly N across the eastern Gulf of Mexico. The key message we
want to get across this period is the heavy rain and flood
threat that is expected to develop late tonight and through Mon.

Mainly isolated to perhaps scattered showers and thunderstorms
are expected to develop as heating gets underway today. The
seabreeze and Piedmont trough should help to focus the ever
present moisture. Widespread showers and some thunderstorms will
arrive from S to N this eve and overnight. Average rainfall
amounts through Mon could easily reach if not exceed 3 to 5
inches with the higher amounts favored nearer to the coast.

Precipitable water values will climb to near or above 2.25
inches which per SPC Climatology is a record for late May at
KCHS. The Excessive Rainfall Outlook produced by WPC has
included the entire forecast area in a slight risk for excessive
rainfall. Model soundings show the moisture deepening through
the later portion of today and becoming very deep tonight as
tropical plume sets up across the eastern Carolinas. A trough
emanating from Alberto is expected to develop NE of the center
and up across the offshore waters of the Carolinas today and
then pivot onshore tonight. Models are also showing several
shortwave troughs advancing N and then NW, well ahead of the
subtropical system. Modest elevated instability coupled with
strong vertical velocities and increased forcing strongly
suggest heavy rain will advance N and into our FA this eve and
overnight. This becomes problematic given the antecedent
conditions as soils are wet to saturated from significant
rainfall over the last week to 10 days. Significant ponding
is likely to develop across some low-lying and poor drainage
areas after dark with the possibility for more serious flooding
toward morning and on Mon. A Flash Flood Watch may be required
with the afternoon forecast package. Developing widespread
nocturnal convection warrants categorical POPs tonight.

Greater cloud cover today as compared to Sat should shave a
degree or two off of the high temps, especially across South
Carolina. We are forecasting mid and upper 80s, but can not rule
out a couple 90 degree temps this afternoon. Highs near and at
the beaches will be in the lower 80s due to a seabreeze
circulation which will kick south winds up to 15 to 25 mph this
afternoon. Lows tonight will be in the lower 70s.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
As of 300 AM Sunday...A wet short term period still in the
cards. At the start of this period, pcpn will be ongoing ie
Categorical POPs. A dry punch associated with Alberto may
partially push across the FA Mon aftn and evening. This will
help to lower the intensity of the pcpn or even temporarily
reduce pcpn coverage to widely scattered. Nevertheless, the
tropical moisture plume will continue to move across the FA Mon
night into Tue before getting shunted east of the FA by late Tue
and/or Tue night. At this point, WPC has the FA in a Slight
Risk with respect to it's Excessive Rainfall Outlook for Day2
and Day3 12z Sun thru 12z Tue. The FA will see widespread 2 to 3
inches this 2 -Day short term period with pockets of 3 to 5
inches possible. If the 3 to 5 inch totals were more widespread
then would lean toward a FFA but at this point will continue to
highlight the heavy rain in the local HWO for the time being.
Overall, as the previous fcst alluded, Mon will basically be a
washout with 100 POPs. POPs will slowly lower to the next
categories, ie. Likely or good chance, come Tue into Tue night.
This slow reduction is due to progged PWs still hanging around 2
inches and therefore not taking much to ignite the development
of both showers and thunderstorms during this block of time. As
for temps, a 10 degree or less diurnal range of temps expected
Monday, followed by an improvement to 10 to 15 degrees on Tue.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 300 PM Saturday...Alberto should begin tracking north from the
Gulf Coast on Tues. The latest models are in fairly good agreement
with keeping the center or remnant low moving north just east of the
Mississippi River then northeast toward the Great Lakes and then
toward the New England coast. This keeps forecast area in a
deep stream of tropical moisture between the Atlantic ridge to
the east and Alberto low to the distant west Tues through Wed
night. The pcp water values remain well above normal, on the
order of 2 to 2.3 inches, Tues through Thurs morning. Any drier
air looks like it may hold off until Thurs aftn into Fri as
winds veer to a more westerly direction in the low to mid levels
as Alberto low reaches up near the Great Lakes. Even with the
column drying out some on Fri, a very moist atmosphere will
remain into Saturday. Small diurnal ranges expected in temps
with low 80s most days and low 70s at night.

Overall, expect a very warm and humid air mass in place with clouds
and rain hanging on through at least Thurs with some breaks
possible by Friday or Saturday. The most widespread rain should
be through mid week but the timing and exact areas of heaviest
rain will not be possible to say at this point, but expect
periods of rain and locally heavy rain through Thurs. The
rainfall should be diurnally enhanced, more widespread inland
during the day and along the coast overnight. The local forecast
area should not see any direct impacts from Alberto, just a
continuous tropical feed of moisture for several days.

&&

.AVIATION /08Z SUNDAY THROUGH THURSDAY/...
As of 06Z...VFR conditions inland are expected to become IFR as
low stratus develops after 08z and persists through about 12z.
Developing BR may drop ceilings to IFR/MVFR as well during this
time. VFR for the remainder of the overnight for the coastal
terminals with periods of MVFR ceilings. Convection today is
expected to be mainly isolated, developing along the seabreeze
this morning and the Piedmont trough later this morning and this
afternoon and will forecast prevailing VFR conditions at all
the terminals for the bulk of the daylight hours although it may
take until mid morning before ceilings lift to VFR at KFLO and
KLBT. Meantime, deep moisture flowing north from the tropics
ahead of Alberto is expected to bring periods of heavy rain in
association with numerous to widespread showers and some
thunderstorms from S to N this eve and especially overnight and
Mon. Will show ceilings and visibility deteriorating to MVFR and
IFR late in the valid TAF period.

Extended outlook...Late Sun and through Mon, IFR with periods of
heavy rain in showers and some thunderstorms. Tue-Thu, tempo
MVFR/IFR in showers and thunderstorms.

&&

.MARINE...
NEAR TERM /THROUGH SUNDAY/...
As of 300 AM Sunday...We have raised a Small Craft Advisory
for the waters beginning tonight, first across the southern
waters this eve and then expanding to include the northern
waters overnight.

S to SSE winds will prevail across the waters into this eve
with S winds overnight. Wind speeds will be up to 15 to 20 kt
beginning this afternoon. Seas will build from 3 to 4 ft today
to 4 to 7 ft tonight.

The Bermuda High will shift away from the area through tonight
as Subtropical Storm Alberto moves slowly N across the eastern
Gulf of Mexico.

SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
As of 300 AM Sunday...SCA will be ongoing at the start of this
period and have it continuing thru Midday Tue. The local waters
will be sandwiched between Alberto well west of the FA and
Bermuda High pressure centered well east of the FA. As a result
of this funneling effect, have leaned toward the hier side of
guidance with respect to wind speeds ie within the 15 to 25 kt
range with hier gusts. Looking at a S wind direction initially
veering slightly to the SSW-SW Mon night thru Tue. WindSpeeds
will be declining during the Tue time- frame. Significant seas
will peak during Monday with all zones seeing 6 foot, or higher
for the waters off Cape Fear and Romain respectively. The
ongoing SE ground swell will get reinforced from upstream. At
the same time, local wind waves Mon combined with the 7 to 9
second swell, will keep seas at SCA thresholds Mon thru Tue
morning. Seas will fall below SCA thresholds midday Tue with
winds having already dropped by this time frame. There will be
widespread showers and embedded thunderstorms reducing VSBY to
frequently to 1 to 3 nm and below 1 NM in heavy rains.

LONG TERM /WEDNESDAY THROUGH THURSDAY/...
As of 300 PM Saturday...Southerly winds will continue across
the waters through Wed, mainly between 5 and 15 kts. the
strongest winds may be early Tues and then again on Thurs as
they veer to a more SW to W direction. The persistent southerly
push will keep seas between 3 and 5 ft most of the period, with
highest seas most likely to start Tues morning and then rising
slightly again Thurs night. As winds lighten and veer Wed night
into Thurs they should drop to the 2 to 4 ft range.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...None.
NC...None.
MARINE...Small Craft Advisory from 8 PM this evening to noon EDT
     Tuesday for AMZ254-256.
     Small Craft Advisory from 2 AM Monday to noon EDT Tuesday for
     AMZ250-252.

&&

SYNOPSIS...
NEAR TERM...RJD
SHORT TERM...DCH
LONG TERM...RGZ
AVIATION...RJD
MARINE...

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