Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
1240 PM EST Wednesday Nov 25 2015
strong high pressure will prevail inland through the weekend...as
a weak coastal trough lingers nearby late this week. The area of
high pressure will weaken somewhat next week as a cold front passes
by to the north.
Near term /through tonight/...
expansive high pressure over the northeast United States will
remain the dominant feature today. The 850 mb ridge is positioned
off the middle-Atlantic coast with a steady east-southeast flow above the cool
surface wedge. Aside from a gradual increase in low level clouds
today due to the isentropic ascent...there will probably not be
enough forcing to support more than a slight chance of rain over
outer coastal waters.
In spite of an increase in cloud cover and an inland wedge...warm
advection and heights climbing aloft in response to a building
middle/upper ridge will allow for temperatures to climb to the middle and upper
60s across most sections. The exceptions will be far north and
immediate SC coast where 60-63f will be more common. It/S also the
coastal sections that will receive the highest winds as the
gradient pinches between the inland wedge and a nearby trough in
the Atlantic. NE winds will peak at 15-25 miles per hour and gusty throughout
Tonight...short wave energy dropping southward around the east
side of the ridging aloft will allow for a cut off low to form
NE of the Bahamas late. Simultaneously at the surface potent high
pressure off New England will strengthen further...as high as 1050
mb...as it/S associated ridge extends inland over the southeast. The
position and orientation of the high allows for the coastal trough
to attempt to slip a little closer to the shoreline of SC and Georgia.
That along with a little greater depth and strength of the east/southeast
low level flow...weak divergence aloft and a little better influx
of maritime moisture will lead to small probability of precipitation for all coastal
counties. Again though the quantitative precipitation forecast looks to be light with precipitable waters only
3/4 to 1 inch or so. Breezy conditions will continue near the
coast...limiting lows to only the middle and upper 50s. But upper 40s
and lower 50s will be the norm further inland.
Short term /Thursday through Saturday/...
an area of strong high pressure extending from south of
Newfoundland southwestward into the Middle Atlantic States will
produce northeasterly winds across the entire County Warning Area on Thursday with
breezy conditions near the coast. Clouds will be thicker closer to
the coast where the marine layer will be advecting onshore...and
there will be a slight chance of showers for the coastal counties
as well...although any rainfall amounts will be light. It will be
a little warmer with highs reaching the lower 70s...although it
will be cooler at the beaches due to clouds and onshore winds.
The overall pattern does not change much on Friday...but the high
pressure does weaken some...so the onshore flow will not be as
strong. Also...the winds may back a little...keeping the worst of
the clouds and showers offshore into the coastal waters.
Therefore...I also think the temperatures will be a couple of degrees warmer
due to fewer clouds and weaker cool advection. Overnight temperatures will
drop into the lower to middle 50s
On Saturday...a weak cold front essentially falls apart as it
approaches the area...allowing for a continuation of mainly dry and
sunny conditions with northeasterly winds and temperatures in the lower 70s
away from the coast.
Long term /Saturday night through Wednesday/...
reinforcing high pressure will build north of the County Warning Area on Sunday
and into early next week...maintaining the mostly dry
northeasterly flow. Temperatures will drop a few degrees will a modest
strengthening of low level cool advection...but should still be in
the middle 60s in the north to near 70 in the south...or fairly close
to normal. A stronger cold front will then approach from the west
for the middle of next week...introducing the best chance for
showers as the surface wedge finally gives way.
Aviation /18z Wednesday through Monday/...
both sites will be generally VFR through 18z Thursday. Some
numerical guidance indicates the potential for MVFR or lower
ceilings at ksav later tonight. The short-range ensembles are not
as impressed given fairly weak moisture return tonight. We hinted
at some lower clouds but maintained VFR at both sites.
Extended aviation outlook...generally VFR conditions are expected
through the period.
enhanced northeast gradient with high pressure to the north will
maintain Small Craft Advisory conditions in all waters outside The
Harbor. In The Harbor we expect 15-20 knots winds.
Tonight...a 1050 mb high will pull east of New England and across
Nova Scotia and Newfoundland...stretching all the way to the
south/SW across the southeast states and Gulf of Mexico. The pinching of
the gradient around the high and due to a subtle coastal trough
near the local waters will allow for winds/seas to remain
elevated...and advisory conditions will remain in effect for all
Atlantic waters. NE winds will again reach 20 or 25 knots...and seas
will be as large as 5-8 feet within 20 nm and 7-9 feet further
offshore. We/ll maintain a close watch on Charleston Harbor just
in case they too need a Small Craft Advisory.
Thursday through Monday...sca/S will be needed for the next
several days due to a combination of winds and seas. An extended
fetch of northeasterly winds from the North Atlantic into the
coastal waters will cause seas to get up as high as 10 feet in the
offshore Georgia waters and as high as 7 feet in the nearshore
waters beyond 10 miles later this week. Winds will come down
slowly by Saturday...but seas will still be high enough to warrant
headlines through the weekend. Conditions will gradually improve
early next week.
we could be close to advisory conditions with the evening high
tide and we/ll re-evaluate that situation later today.
Coastal Flood Advisory criteria will be easily met with the Thursday
morning high tide...and this also looks like the best chance for the
area to reach warning criteria of 8 feet MLLW in chs and 10 feet
MLLW at fort Pulaski. Coastal flood watches for Thursday morning may
be needed later today.
For Friday and beyond...both the surge and astronomical forcing will
be slowly diminishing...but not enough to avoid Flood Advisory level
criteria during the time of the morning high tide into Saturday.
With the King tides and long fetch of the next couple of days...a
high surf advisory is also a possibility during the second half of
the week. Seas will build to as high as 4 to 7 feet in the nearshore
waters with decent breakers at the shoreline. Beach erosion in
vulnerable locations appears likely as well.
Marine...Small Craft Advisory until 6 PM EST Sunday for amz350-352-354-