Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 252314
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
714 PM EDT WED MAY 25 2016

.SYNOPSIS...
Atlantic high pressure will prevail through Friday. A wave of low
pressure is then expected to develop over the western Atlantic and
approach the southeast coast as early as this weekend. The
forecast then becomes quite uncertain as the low could meander off
the southeast coast into early next week.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
Tranquil weather on tap tonight with high pressure in control.
Generally clear skies and light winds will prevail making for
decent radiational cooling with temperatures falling to near
normal levels...lower to mid 60s inland/lower 70s at the coast.
Some patchy fog cannot be ruled out toward daybreak but confidence
is low and thus we left out of the forecast.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
Thursday and Thursday night: Atlantic high pressure at the surface
remains in place under broader mid and upper level ridging.
Sufficient moisture in the lower levels supports a shallow cumulus
field developing during the day, but it is anticipated that the area
will remain precipitation-free given the larger-scale subsidence in
place. Temperatures will remain nearly seasonable, with highs
generally in the upper 80s inland...lower near the coast, and lows
in the mid to upper 60s.

Friday and Friday night: An upper level trough persists over the
Bahamas located near remnants of a stalled surface front, and for
the last several days computer models have routinely developed this
interaction into a wave of low pressure that then begins to
translate towards the SE US coast. Locally, Friday looks to remain
similar to Thursday with virtually no chance for precipitation and
temperatures hovering right around seasonal values.

Saturday: The forecast for the remainder of this period becomes
difficult. While model consensus maintains the development of this
low pressure, individual solutions continue to vary in the ultimate
movement and peak intensity of this system. The GFS and ECMWF
continue to depict a system that approaches the coastline as early
as Saturday evening between northern FL and SE South Carolina and
then meanders off the coast through at least Monday, while the
Canadian develops a stronger circulation that moves with more
purpose. Thanks in part to at least these two distinct
possibilities, forecasting the specific local impacts remains
difficult at this time. At this juncture, the forecast will continue
to depict POPs and a chance for thunderstorms increasing from the
east beginning Saturday morning and a slightly narrower diurnal
variation in temperatures coincident with expected increases in
cloud cover. At this time, most likely impacts to the area on
Saturday seem to be periods of heavy rainfall, an elevated risk of
rip currents, and beach erosion, though even the predictability of
these impacts remains low this far in advance.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
As of Wednesday morning, the National Hurricane Center has
indicated that there is a 50 percent chance for tropical or
subtropical development off the southeast coast within 5 days.

Forecast confidence is quite low for the long term period and the
details of the forecast hinge significantly on the status, strength,
and eventual track of an area of low pressure expected to be sitting
off the southeast coast starting Saturday night. Attempting to nail
down specifics in such an uncertain forecast at this point would be
an exercise in futility. Instead we will have to wait and see how
the large scale environment unfolds and what impacts the wave of low
pressure will have on the forecast area. Overall, the system appears
as though it will be an environment with very weak steering flow
which would seem to favor a system that could meander about with
little forward progress. Another thing to keep in mind is that the
system is progged to be sitting over the Gulf Stream, possibly into
early next week. Within a weak steering flow environment it may be
difficult to envision the system moving off the Gulf Stream and may
favor a slow offshore track. Much is yet to be determined and the
forecast will be refined a model consensus develops.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
VFR through 00Z Fri. Low probability for ground fog around
daybreak Thursday.

Extended Aviation Outlook: VFR conditions expected through at least
Friday. Flight restrictions are possible at either terminal
beginning as early as Saturday with an approaching low pressure
system.

&&

.MARINE...
Tonight: The sea breeze circulation will maintain S/SE winds 10-15
kt into early evening. Offshore high pressure will then maintain
a S/SE synoptic flow with speeds mainly averaging 10 kt or less
tonight. Seas will remain 1 to 3 feet, highest well offshore.

Thursday through Sunday: High pressure over the Atlantic will
prevail into Friday when a developing wave of low pressure is
expected to track eastward toward the southeast coast. The
forecast is then quite uncertain for the weekend and will
ultimately be determined by the location, strength, and track of
the wave of low pressure. As it stands for now, the forecast
features a rather modest northeast flow with speeds generally no
more than 15 knots. Seas top out in the 2-4 ft range with some 5
ft seas possible in the outer waters this weekend as the northeast
fetch increases.

Rip Currents: An increased risk of rip currents for the upcoming
holiday weekend is probable as onshore flow and swell energy
increases in advance of an approaching low pressure system.

&&

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

&&

$$
SYNOPSIS...
NEAR TERM...RJB
SHORT TERM...JMC
LONG TERM...BSH
AVIATION...JMC/RJB
MARINE...JMC/SPR



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