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Area Forecast Discussion

FXUS62 KCHS 260151

Area Forecast Discussion
National Weather Service Charleston SC
951 PM EDT THU AUG 25 2016

High pressure will prevail into the weekend. A weak surface trough
will develop over the region by late weekend and will persist
through the middle of next week.


Thursday was the 65th straight day of 90 degrees or greater at
Savannah (KSAV).

Tonight: The bulk of the atmosphere is under the influence of
strong anticyclonic flow, with the exception of the upper levels
where analysis reveals a weak TUTT low spiraling over NE Florida
and drifting SW. Considerable dry air (PWat 1.15 inches at 00Z as
per KCHS sounding) within the large scale sinking motion and the
lack of any appreciable low level convergence will allow for
another rainfree night. If there are any showers they will stay
out near the western wall of the Gulf Stream closer to daybreak.

Mainly clear to clear skies and calm or light winds away from the
immediate shoreline will allow for good to excellent radiational
cooling. But since dew points are not as low as 24 hours ago, we
won`t get quite as cool as last night. Expect minimum temps near
or just below normal for this time of year.


Friday: A large mid/upper lvl ridge of high pressure will prevail
over the Southeast late week, generally favoring rain-free
conditions over all locations while subsidence occurs and pwats
remain at or below 1.0 inch for most of the area. In general, high
temps should peak in the low/mid 90s. Overnight lows will range in
the lower 70s inland to mid/upper 70s near the coast Friday night.

Saturday and Sunday: Very little change is anticipated in the
overall pattern this weekend into early next week. However, models
continue to suggest that the mid/upper ridge of high pressure
responsible for dry weather over the Southeast will nudge further
north/northeast as a trough of low pressure begins to develop over
the region late Sunday. The setup should allow a more direct onshore
flow and increasing levels of moisture to advect over the region
from the Atlantic. Given sufficient sfc heating each day, expect at
least slight chances of showers/thunderstorms during peak diurnal
heating each day. However, the best chance of precip will likely
remain in southern Georgia counties on Saturday, before increasing
coverage in Southeast Georgia and Southeast South Carolina on
Sunday, mainly due to a more active seabreeze. Overall, high temps
are expected to range in the low to mid 90s away from the coast each
day. Overnight lows will range in the low/mid 70s away from the
immediate coast.


Independent of the development of a tropical entity that evolves
from a disturbance located near Hispaniola and moving WNW toward the
Florida peninsula, a shift to deep-layered troughing should
translate to a greater chance for showers/thunderstorms during this
period, especially during the Tuesday through Thursday time frame.
After another day with high temps in the lower/mid 90s Monday, the
greater potential for clouds/precipitation is reflected in near
normal temperatures in the upper 80s/lower 90s Wednesday and
Thursday. Lows should range in the mid 70s inland to around 80 along
the coast through this period.

As of Thursday evening, the National Hurricane Center indicated a
medium chance for tropical development within a zone from north
of Hispaniola to southern Florida within 5 days, and guidance
generally agrees that a tropical system will be located in the
vicinity of south Florida later this weekend. Thereafter, guidance
has generally trended toward a solution which turns the tropical
system toward the north, either over the Gulf of Mexico or near
the western Florida coast, perhaps carrying low pressure over land
and across our area with a threat of heavy rain and potentially
severe weather for mid to late week. However, due in part to the
uncertain rate of weakening of the deep-layered ridge currently
over the area and a highly uncertain tropical cyclone
track/intensity forecast beyond this weekend, the latest forecast
does not explicitly account for any impacts from a recurving
tropical cyclone next week.



Extended Aviation Outlook: VFR conditions are expected at both CHS
and SAV terminals.


Tonight: A narrow ridge of Atlantic high pressure squeezed between
a cold front to the distant NW and lower pressures to the SE will
prevail across the local waters. E winds around 12-18 kt early on
will diminish to 15 kt or less thereafter. Winds will back to more
solid NE or even NNE flow late near the coast and in Charleston
Harbor due to the cooling land breeze. A little 1-2 ft swell from
the remnants of "Fiona" and persistent onshore fetch will combine
with shorter period wind waves to give us average seas of 3-4 ft.

Friday through Tuesday: High pressure will dominate the coastal
waters through Saturday, before giving way to a weak trough of low
pressure advancing into the area this weekend. The setup will favor
east/northeast winds between 10-15 kts with gusts as high as 20 kts
in offshore Georgia waters into early next week, before winds become
more east/southeast in response to low pressure entering the area.
Seas will slowly build from 2-4 ft to 3-5 ft this weekend into early
next week. There is a chance that offshore Hurricane Gaston could
push a long period swell as high as 6 feet into waters beyond 20 nm
early next week.

Rip currents: Persistent onshore winds and a small long period swell
could begin to produce an elevated risk of rip currents this weekend.
A larger and longer period swell produced by Hurricane Gaston could
begin to reach the coast early next week and this could set the
stage for stronger/more frequent rip currents.


Tides have been running above extratropical surge guidance but have
remained just below Coastal Flood Advisory levels for the past
couple of days. This scenario will likely repeat around the times of
the afternoon high tides through this weekend as E/NE winds prevail.
There is a chance that the influence of the Sept. 1 new moon and
a larger swell produced by offshore Hurricane Gaston could combine
to push evening high tides past Coastal Flood Advisory levels next





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