Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
419 PM EDT Tuesday Oct 6 2015
low pressure off the South Carolina coast will move farther
offshore through tonight. High pressure will build into the
region through Friday. A weak cold front will approach from the
northwest this weekend.
Near term /until 6 am Wednesday morning/...
this evening and tonight...a pronounced middle/upper level low depicted
over the western Atlantic on water vapor imagery will continue to
shift northeast and away from the area through tonight. At the
surface...low pressure will track northeast well offshore while dry high
pressure builds over the area from the west. The pattern will favor
clearing skies from northwest to southeast this evening into early
overnight hours...supporting favorable conditions for cooler temperatures
later tonight. In general...temperatures should dip into the middle 50s
inland to low 60s along the immediate coast.
Short term /6 am Wednesday morning through Friday/...
Wednesday and Wednesday night...a long wave middle and upper level
trough will continue to shift offshore as surface high pressure
builds in from the Great Lakes region. Despite considerable
sunshine...northeast flow will keep highs around 80 across much of
the forecast area. Lows at night will be in the upper 50s inland
with lower to middle 60s near the immediate coast.
Thursday and Thursday night...a nearly zonal flow will develop aloft
as surface high pressure builds down the eastern Seaboard. A
developing onshore flow mainly down along the Georgia coast will
result in a slight increase in cloud cover...and could not totally
rule out an isolated shower near the coast mainly south of I-16.
Some rising heights aloft should produce highs in the lower to middle
Friday...an upper level trough will move across the Great Lakes
region...pushing the surface high offshore and allowing more of a
southerly flow to develop. Deepening moisture profiles could allow
for some isolated convection to develop...mainly in areas closer to
the coast. Highs should maintain in the lower to middle 80s.
Long term /Friday night through Tuesday/...
Friday night the front continues to approach from the northwest...
but it will be weakening. Moisture associated with this front
will allow for the risk of light showers across most of the
County Warning Area...except for the interior Georgia zones...which should remain
dry. Saturday the weakening front will clip or pass just north of
our County Warning Area...leading to continued showers. Late Saturday into Sunday
high pressure builds back towards our area...possibly setting up
another wedge pattern. Expect dry conditions Sunday and Monday
with seasonal temperatures.
Aviation /20z Tuesday through Sunday/...
VFR conditions prevail at both terminals through 18z Wednesday.
Extended aviation outlook...VFR will prevail through Friday.
Conditions may deteriorate Friday night into Saturday as a front
approaches from the northwest.
this evening and tonight...an enhanced pressure gradient will
persist over parts of our coastal waters between high pressure
inland and low pressure offshore...favoring the continuation of
small craft advisories over northern SC waters and offshore Georgia
waters into evening hours. The pressure gradient will then relax
overnight...resulting in winds/seas that decrease/subside.
Conditions over the northern SC waters are expected to fall below
Small Craft Advisory conditions by midnight...possibly sooner as
seas subside below 6 feet. However...lingering 5-7 feet seas will result
in the continuation of a Small Craft Advisory in offshore Georgia
waters through the overnight period. Elsewhere...expect north winds
between 10-15 kts...with seas no higher than 3-5 feet.
Wednesday through Saturday night...Wednesday northeast winds of
10-15 knots will persist across the waters. The Small Craft Advisory
will remain in effect for the Georgia waters beyond 20 nm (zone 374) due
to seas remaining around 6 feet into Wednesday evening. This is the
result of a remnant NE swell. Wednesday night into Thursday the seas
in zone 374 should subside to 4-5 feet...which will allow the advisory
to expire. A wedge pattern will also start to develop on Thursday
but winds should remain around 10-15 knots. A weakening cold front
approaching from the northwest should cause winds to turn southerly
late Friday...and then northwest on Saturday as the front moves out
to sea. No advisories are expected Friday or Saturday.
areal flooding...flood waters left by historic rainfall will slowly
recede over the next few days. Although some areas will see slow
improvement...spots near the edisto and Santee rivers could see
worsening conditions as river levels rise.
River flooding...moderate flooding is expected for the Santee river
near Jamestown for the next several days...but major flooding will
be possible early next week. Major flooding is also forecast for the
edisto river near Givhans Ferry starting tonight. River flood
warnings remain in effect for both points.
coastal flooding...a coastal Flood Advisory remains in effect until
7 PM this evening for the entire lower South Carolina coast based on
the latest tide trends. At this time...forecast tides in the
Charleston Harbor should reach 7.4 to 7.6 feet MLLW. This will
result in moderate salt water coastal flooding. Coastal flood
advisories or coastal flood warnings will be needed around times
of high tide for much of this week.
Rip currents...2-3 feet swells every 12 seconds will produce a
moderate risk of rip currents along the lower South Carolina
coast. The risk is a bit more marginal for the upper Georgia
coast. Will maintain a low risk for this area...although a
moderate longshore current will likely be present.
SC...coastal Flood Advisory until 7 PM EDT this evening for
Marine...Small Craft Advisory until midnight EDT tonight for amz350.
Small Craft Advisory until midnight EDT Wednesday night for