Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 251709
AFDILM

Area Forecast Discussion
National Weather Service Wilmington NC
109 PM EDT Fri May 25 2018

.SYNOPSIS...
Warm and humid early summer conditions will prevail into the
holiday weekend, accompanied by scattered showers and a few
thunderstorms. Tropical system Alberto will move into the Gulf
of Mexico Saturday, reaching the Gulf coast and stalling there
much of next week, before drifting north. For the Carolinas,
expect periods of rain, heavy at times, late Sunday through
much of next week. With already wet ground, this may lead to
problematic flooding in some areas.

&&

.NEAR TERM /THROUGH SATURDAY/...
As of 1045 AM Friday...Faint frontal boundary remains oriented
east to west across SE NC and NE SC this morning, which may
reveal itself a bit better in developing cu/convective fields.
Low level convergence resulting from a inland advancing sea-
breeze, will push the focus for showers and storms toward the NW
and N through the day, nearly clearing the forecast area by 6-7
pm. While SE NC may see convection, a sharp PWAT gradient noted
in MHX/CHS raobs, and also evident in low-level water vapor,
will favor rain the higher coverage and intensity over NE SC.
Storm motion little faster today and PWATS down a little bit,
so the localized flood threat overall is more limited today. It
appears the set-up is favorable for ocean showers or an isolated
TSTM to brush the Cape Fear area overnight into daybreak
Saturday.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
As of 300 AM Friday...Western Atlantic ridge will drift a
little further S and E this period. At the same time, low
pressure will be deepening as it moves slowly N across the
eastern and central Gulf of Mexico. Model consensus is that a
tropical or perhaps a subtropical area of low pressure will be
strengthening as it nears the Gulf Coast. The tropical cyclone
may be located somewhere between the western FL panhandle and
New Orleans early Mon morning.

For the eastern Carolinas, direct impacts from this system are
unlikely. However, a deep tropical flow of moisture will feed N
between the Western Atlantic ridge and the developing area of
low pressure, bringing widespread showers and thunderstorms and
heavy rainfall. Precipitable water values will likely peak near
or in excess of 2.25 inches which would be a record based on
upper air information dating back to 1948 at Charleston, SC for
the waning days of May. Current forecast has average rainfall
amounts of 1.5 to 2.5 inches with the brunt of this falling
later Sun and through Mon. Higher amounts are certainly possible.

For Sat, expect the convection will be diurnally driven with the
seabreeze and Piedmont trough acting as boundaries of initiation.
Typically, showers or a thunderstorm will threaten the beaches
during the morning through about midday and then move further
inland with the seabreeze. Areas further inland should be more
at risk for showers or thunderstorms during the afternoon and
early eve. Moisture content of the atmosphere will be high on
Sat, although not as high as later in the forecast period. Given
ridging in place and the lack of upper level support, will cap
POPs at chance with no POPs during the late eve and overnight.

For Sun, will show convection increasing from S to N with
categorical POPs overspreading the FA during the eve and
overnight. We have added heavy rainfall to the gridded forecast.
Given the antecedent conditions, we will be considering the need
for a Flash Flood Watch with later forecast packages should our
confidence in a widespread heavy rainfall event continue to increase.

High temps will be in the upper 80s inland on Sat with lower to
mid 80s nearer to the coast with the beaches expected to top out
around 80. Lower to mid 80s should be common for highs on Sun.
Lows both nights will be mainly in the muggy lower 70s with
perhaps a few upper 60s thrown in across some inland areas.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 300 PM Thursday...The pattern through the extended period
will remain very moist and supportive of scattered to numerous
showers and thunderstorms each day. Precipitable water values
in excess of 2 inches will remain through Thursday. Similar to
the several days, this moist airmass will be fed by deep
southerly flow between Bermuda high pressure, and a trough axis
along the Mississippi River Valley extending into the Gulf of
Mexico. A contributing factor will be the northward progression
of a possible tropical or sub-tropical low pressure system
through the Gulf of Mexico. Although direct impacts from this
potential tropical system are not currently expected for our
forecast area, this feature will ensure a continued feed of
tropical moisture across the eastern Carolinas.

&&

.AVIATION /17Z FRIDAY THROUGH TUESDAY/...
As of 18Z...Isolated showers are occurring SW-W of KILM, and W
of  KMYR. Confidence is moderate to high all coastal terminals
will remain VFR this afternoon. Worse case VCSH as showers
should develop inland, then move away from the coast. If a tempo
shower were to occur, highest confidence would be KILM. Other
showers are occurring SE-S of KFLO. There is higher confidence
of tempo showers with possibly an isolated thunderstorm this
afternoon at KLBT/ possibly KLBT in the late afternoon. Will
show tempo MVFR with VCTS in KFLO TAF early afternoon, late
afternoon at KLBT. Convection slowly dissipates 01-04Z. As the
night progresses tempo MVFR cigs will become possible at the
coastal terminals along with possibly an isolated shower. Tempo
IFR can be expected at the inland terminals. VFR expected at all
terminals after 14-16z with SSW-SW winds.

Extended outlook...VFR except for morning patchy MVFR/IFR in
fog.  Tropical moisture will be returning to the area Sun-Wed
with more widespread thunderstorms with periods of IFR
ceilings/visibility possible.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
As of 1045 AM Friday...SE waves around 2 feet every 7-8 seconds
will mix with light to moderate southerly chop. This regime to
prevail today and overnight. Expect inshore gusts near 20 kt
between 2 pm-5 pm.

As of 300 AM Friday...Easterly winds of ten knots or less will
continue through the morning hours across the waters. Later today
sea breeze influences and a final dissipation of a residual boundary
will switch winds back to the south increasing to 10-15 knots. These
conditions should prevail through early Saturday. Significant seas
will remain 2-3 feet.

SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
As of 300 AM Friday...Western Atlantic ridge will drift a
little further S and E this period. At the same time, low
pressure will be deepening as it moves slowly N across the
eastern and central Gulf of Mexico. Model consensus is that a
tropical or perhaps a subtropical area of low pressure will be
strengthening as it nears the Gulf Coast. The tropical cyclone
may be located somewhere between the western FL panhandle and
New Orleans early Mon morning. For the Carolina waters, this
means deteriorating marine conditions, especially Sun night and
Mon.

A robust seabreeze should bring wind speeds up to 15 to 20 kt
Sat and Sun afternoon and eve. Seas will build from 3 to 4 ft
Sat to 5 to 7 ft Sun afternoon and night. A SE swell on the
order of 7 seconds will be energized later Sun and especially
Sun night. Showers and thunderstorms with heavy rain are
expected to become widespread Sun night and this will result in
poor visibility.

LONG TERM /MONDAY THROUGH TUESDAY/...
As of 300 PM Thursday...Southerly flow will persist across the
waters between Bermuda high pressure and a low pressure system
that will be moving northward through the eastern Gulf of
Mexico. Conditions will depend on how much the low is able to
develop in the Gulf, but the persistent southerly fetch and
strengthening gradient should support winds of 15 to 20 knots
and seas of 5 to 7 feet. By Tuesday, models suggest the
gradient will weaken a bit, which would allow winds to diminish
to 10 to 15 knots, and seas to slowly subside. Uncertainty is
higher than usual at this point, however, due to the potential
for the Gulf low to develop into a tropical cyclone.

&&

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

&&

$$

SYNOPSIS...8
NEAR TERM...MJC
SHORT TERM...JDW
LONG TERM...RGZ
AVIATION...MRR/8



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