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Area Forecast Discussion

FXUS62 KCHS 261352

Area Forecast Discussion
National Weather Service Charleston SC
952 AM EDT THU MAY 26 2016

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.


For the late morning update, hourly temperatures have been
adjusted to account for slightly faster than expected rates of
warming. Anticipated maximum temperatures for today, as well as
the rest of the forecast parameters, remain on track.

The weak mid-level shortwave continues its slow trek across
northern GA within a broader ridge blanketing the SE states, and
will tend to dissipate across North Georgia and the Western
Carolinas through today. Mid level moisture and instability
conducive for deep convection will remain west of our forecast
area, thus we maintained a dry forecast. Moisture from 850 mb and
700 mb will be somewhat higher this afternoon than on Wednesday,
leading to a diurnal cumulus field that may be somewhat greater
in coverage than on Wednesday. As the sea breeze moves inland,
cannot completely rule out a few spotty showers inland from the
coast this afternoon. Any rain would be very brief/isolated and we
maintained pops 10% or less. Stable mid levels should preclude any
risk of deep convection. Highs will be the mid to upper 80s most

Tonight: The weather will remain tranquil with mostly clear skies
and low temps in the lower to mid 60s with near 70 temps on the
beaches and barrier islands.


Friday and Friday night: Deep and prominent ridging will remain in
control aloft as the axis of the ridge protrudes inland through the
mid-Atlantic region around the disturbance situated north of the
Bahamas. At the surface, high pressure will continue to extend into
the region from the northeast before starting to break down late
Friday night as the Atlantic low approaches. Deep dry air and
subsidence will be in place, until some potential moistening occurs
late. All the models continue to show showers and storms rotating
around the developing offshore low and approaching the coast toward
daybreak Saturday. Have kept pops in the slight chance range, mainly
along the Charleston County coast. Otherwise, a very quiet day and
night period with highs in the upper 80s to near 90 and lows in the
mid to upper 60s.

Saturday through Sunday: This continues to be the period of the
forecast where the complexity increases and confidence decreases
significantly. In a general sense, there is good model consensus
that a area of low pressure will be sitting about 275-325 miles
southeast of Charleston Saturday morning. The consensus then
continues through the remainder of the day with the low moving to
the northwest and drawing closer to the coast, basically maintaining
its rather modest strength. It`s from here that the major forecast
questions arise including what will be the character of the storm,
how strong will it be, and what track will it take. The most recent
outlook from the National Hurricane Center gives the system a 60
percent chance of developing into a tropical or subtropical cyclone,
and this tropical/subtropical difference is further supported by
phase diagrams which show at best a marginally symmetric warm-core
system. Regarding the track, the most recent model runs and invest
AL91 tracks suggest a more progressive system than in recent days.
There is still a lack of a consensus of track and speed, but most
models seem to bring the center of the system to a point near the
central and upper South Carolina coast by late Saturday. With such
significant questions ongoing about the system, it remains difficult
to assess what (if any) possible impacts there will be. For now, the
forecast has been kept steady state and features mid range chance
pops with showers and thunderstorms. As it stands, locally heavy
rainfall could be possible through the weekend, but there is little
to no confidence in exactly where the most rain would fall. Stayed
tuned to NWS Charleston forecast updates as well as the latest
information from the National Hurricane Center.


As would be expected, the long term forecast period continues to be
very low confidence thanks to possible impacts from an area of low
pressure near the South Carolina coast. The details of the forecast
continue to be heavily dependent on the exact track and strength of
the system, so the details in the current forecast should carry
little weight. Recent models runs seem to be a bit more progressive
than they were 24 hours ago, perhaps favoring a shorter time period
of possible impacts. The GFS and ECMWF now take the system to the
north or northeast of the forecast area by Tuesday, but the lack of
run to run consistency makes it hard to jump on any potential trends
as of yet. Two of the possible scenarios include this more
progressive track (which would likely result in a drier forecast)
and the slower more meandering solution noted up until this point
(which would likely result in a wetter, more active forecast). The
forecast is essentially unchanged for now, featuring days of chance
pops, until a discernible model trend develops. Continue to stayed
tuned to the latest forecast updates from NWS Charleston as well as
the National Hurricane Center.


VFR through 12Z Fri. Low probability for ground fog around daybreak
friday morning.

Extended Aviation Outlook: VFR conditions will continue through Friday.
Chances for at least periodic flight restrictions then increase this
weekend and beyond as a low pressure system approaches from the


The low level synoptic flow will tend to very slowly back as the
surface ridge axis eases north ahead of the advancing low pres
wave to the ne of the Bahamas. Through tonight...s to se flow
will back to a more se to e component by daybreak on Friday. The
gradient will remain light with wind speeds 10 kt or less and seas
1 to 3 ft...highest over coastal waters well offshore later tonight.

Friday through Monday: After high pressure prevails across the local
waters on Friday, confidence in the details of the forecast
decreases significantly this weekend and into early next week as a
area of low pressure approaches from the east. As the low approaches
through Saturday, northeast flow is expected to prevail with the
strongest period of winds coming Saturday and Saturday night with
winds potentially getting as high as 15-20 knots. Thereafter,
uncertainty regarding the strength and track of the low becomes an
issue and confidence is diminished. At the very least there will be
the potential for increasing seas and small craft advisory may
eventually be needed, depending on the nature of the storm. Mariners
are urged to remain aware of forecast updates from NWS Charleston as
well as the National Hurricane Center regarding possible tropical or
subtropical development and any associated impacts through early
next week.

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





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