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000
FXUS62 KCHS 261433
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1033 AM EDT Sat May 26 2018

.SYNOPSIS...
High pressure over the Atlantic will extend westward into the
forecast area today. A conveyor belt of deep tropical moisture
on the east side of Tropical Cyclone Alberto will move overhead
Sunday then linger, resulting in unsettled weather through the
middle of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
10:30 AM: Very minor changes made to the forecast, mainly to the
current temperature and dew points to mesh them with the ongoing
forecast. Showers and thunderstorms are starting to form along
the sea breeze and expect them to trend inland, into areas of
higher instability. But the severe threat remains low. Depending
on the convective coverage, we may need to adjust the hourly
temperatures further.

Rest of today: Deep layered ridging extends from offshore into
eastern GA and the coastal Carolinas. Sufficient moisture and
diurnal instability/thermodynamics look to exist for scattered
showers and tstms along and inland from the sea breeze. Somewhat
deeper convection is probable this afternoon over inland GA
zones where over 2500 J/KG SB Capes are possible and environment
lapse rates are just a bit steeper adjacent to the
CSRA/Midlands. Moisture is also deeper in this region thus
DCAPES should be unimpressive. The overall risk of severe storms
remains low although a few stronger updrafts could pulse up at
times.

Tonight: Although even deeper tropical moisture will be
approaching from the south overnight, most areas are expected to
squeak out a dry night after early evening convection inland
wanes. We will probably see patchy low clouds form again well
inland and perhaps some fog adjacent to the upper Savannah
River. Lows will remain quite consistent in the upper 60s to low
70s.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY/...
A plume of exceptionally deep tropical moisture (PWats 2-2.5 inches,
3 standard deviations above normal) advecting northward on the
eastern side of Alberto will spread over the area Sunday as the
tropical cyclone approaches the Gulf Coast. Guidance continues to
consistently show a rainband-type structure containing widespread
moderate to heavy rainfall forming along a surge of high theta-e air
and a coupled jet structure that will begin to approach the area
from the south Sunday morning, slowly working across the area Sunday
afternoon through early Monday morning. We have collaborated with
WPC to bring a slight chance of excessive rainfall across the area
for Sunday and Monday. Much of the area will see 2 to 3 inches of
rainfall during this time, with amounts in excess of 3 inches mainly
focused across the Charleston Tri-County area. Given the relatively
wet antecedent conditions currently in place (several inches of rain
have fallen across most areas away from the immediate coast over the
past week), localized flooding issues are possible. Additionally,
any heavy rain falling near the coast around the time of high tide
Sunday evening could result in significant issues as high tide is
currently forecast to approach coastal flood level.

A more diurnal rainfall pattern will ensue Monday evening, with
storm coverage and intensity waning overnight, then becoming greater
with the increase in thermodynamic instability during the day
Tuesday. A few strong thunderstorms producing gusty winds are
possible Monday and Tuesday afternoons as CAPE values climb to near
1500 J/kg for areas that receive some sunshine, but the overall
severe risk is low in such a deeply moist environment lacking
substantial shear/winds aloft.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
Active weather will persist through the middle-to-end of the week as
deep tropical moisture remains in place. The lack of any larger
scale forcing will result in a primarily diurnal trend for the POP
forecast, with chance-to-likely most days and low-end-to-slight
chance overnight. The flooding threat will decrease, though local
issues cannot be ruled out given the ample moisture available to
storms mainly Wednesday and Thursday afternoons.

High pressure centered near the Bahamas will slowly assume control
of the local pattern as we head into next weekend, bringing more
settled conditions. Temps will trend from near to marginally above
normal through the period.

&&

.AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
VFR conditions likely to persist through the 12Z TAF cycle into
daybreak on Sunday. The main forecast quest is convective
initiation and advancement inland with the sea breeze from late
morning through early this afternoon. We maintained VCSH through
early afternoon at both sites with thunder a possibility but
too uncertain at this juncture. South to southeast breezes will
strengthen a bit in the wake of the sea breeze this afternoon.

Extended Aviation Outlook: Occasional to frequent ceiling and/or
visibility restrictions can be expected at the terminals Sunday
evening through Monday morning as an area of moderate to heavy
rainfall crosses the area. VFR conditions will prevail thereafter,
though continued unsettled conditions mean that brief periods of
flight restrictions in showers and thunderstorms are possible mainly
in the afternoons.

&&

.MARINE...
South to southeast winds remain light this morning, but should
begin a gradual uptick with the onset of the sea breeze along
with a slightly tighter low level pressure gradient later today
and tonight. Speeds should increase closer to 15 kt both in the
Intra-coastal and adjacent waters later today with 10-15 kt
speeds tonight across the marine waters. Seas will range from 2
ft this morning to 2-4 ft by tonight, highest beyond 20 NM
offshore.

Persistent southerly winds will bring increasing windswell into the
coastal waters Sunday into Monday. A Small Craft Advisory will
likely be needed beginning midday Sunday as seas climb over 6 ft for
the offshore Georgia waters, and possibly the nearshore South
Carolina waters as well. Seas will return to the 2 to 4 foot range
with moderate southwest winds mid-week as high pressure near the
Bahamas takes control.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.

&&

$$
NEAR TERM...
SHORT TERM...
LONG TERM...CEB
AVIATION...
MARINE...