North Atlantic Marine Weather Discussion

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AGNT40 KWNM 092032
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
332 PM EST Sun Dec 9 2018

.FORECAST DISCUSSION...Major features/winds/seas/significant 
.weather for the North Atlantic Ocean W of 50W from 30N to 50N.

Over the short term, ASCAT overpasses from this morning indicated 
widespread gales occurring from near Hatteras Canyon south and
southwestward over the central and southern NT2 offshore waters.
These winds aligned quite well with the ongoing OPC forecast. Low
pressure located about 60 NM S of Charleston, S.C. according to
the 18Z preliminary OPC-NCEP surface analysis will move NE
tonight with storm force winds likely developing within the next
3-6 hours especially near the west wall of the gulf stream E and
NE of Cape Hatteras. As the low tracks further NE overnight the
stronger winds will shift E with a second low forming E of Cape
Fear, N.C. early Mon. This low will track generally eastward Mon
into Mon night, before turning NE and intensifying as it moves
away from the offshore waters Tue into Tue night. Another area of
storm force winds will likely develop with this second low as it
pulls E and NE away from the area Tue. Slowly improving
conditions can be expected Tue night as this low moves further NE
away from the waters with some potential for hurricane force
winds at that time, well E of the offshore waters. Forecast
confidence levels are above average for gales over portions of
the waters into Tue, and near average for storm force winds over
the zones indicated below. Scattered strong thunderstorms may
also accompany each low pressure area and associated frontal
boundaries as the cross the region tonight into Tue. Currently
the latest GOES-visible imagery and lightning density data show a
few scattered thunderstorms off the Georgia and Carolina coasts
moving generally toward the NE. Caution is advised for very gusty
winds and very rough seas in and near any of the heavier 
thunderstorms that cross mainly southern and central NT2 
offshore waters over the next 24-48 hours, with winds exceeding 
gale force likely. For the late afternoon package, we will remain
close to the previous grids into Mon, then transition more toward
the consistent 12Z ECMWF guidance later Mon into Tue night over
the waters and use the smart tool which will boost the ECMWF
winds up to 15 percent or so over and E of the gulf stream. The
ECMWF remains just about in the middle of the guidance envelope
into Tue night over the waters, with the 12Z GFS appearing to be
a little too far N with the second low as described above.

Over the medium range, we will continue to populate grids with
the 12Z ECMWF winds for Wed through Fri night over the waters,
and use the boost tool into Thu as noted above. For Fri night we
will boost winds 5-10 percent over the warmer waters of the 
southern and central NT2 waters, but cap winds at 40 kt, until
better model agreement develops over the next few days.
Intensifying low pressure will be moving NE away from the region
Wed as high pressure builds SE from eastern Canada. The high will
then build SE over the region later Wed night into Thu. The high
will begin to move SE from the New England waters Thu night as a
coastal trough or front forms just off the SE U.S. coast. The
high will then shift E of the region Fri into Fri night as low 
pressure moves from the SE states to the South and North 
Carolina coasts. As there remains a good deal of spread in the
12Z model guidance regarding both the location and the intensity
of the low impacting the waters Fri and Fri night we have decided
to cap winds as noted previously, but we feel confident enough
to add lower end gales to the offshore forecast for Fri night as
noted below. Additional adjustments to the hazards and forecast
are likely over the next few days. Please closely monitor the 
latest OPC forecast.

.Seas: For the afternoon package, we will blend in about 20
percent of the 12Z WAM wave guidance for tonight into Mon and
adjust grids to fit current conditions and nearby coastal WFO and
TAFB grids, with a continued boost of up to 10-15 percent in the
gulf stream into Mon night, with as noted previously, the wave
and current interactions within these counterflow scenarios over
the gulf stream will produce locally higher wave heights with an
locally enhanced steepening of the waves and a large gradient in
wave heights across short distances, all resulting in a 
dangerous sea state for the next 36 to 48 hours over the NT2 
waters. For Mon night into Fri night we will rely on the 12Z WAM
guidance with continued enhancements in the gulf stream to match
the wind forecast.

.Extratropical Storm Surge Guidance: As the onshore winds 
continue to increase and shift northward off the southeast US 
coast through tonight, surge should also steadily increase and 
shift N. Water level anomalies seem to be generally running 
about + 1,0-2.0 ft along the Georgia, South Carolina, and parts 
of the North Carolina early this afternoon. The 12Z ETSS, and to 
a somewhat lesser extent, the 12Z ESTOFS both still appear 
underdone at the moment and are likely too low through the near 
term. Interests along the mid-Atlantic and Southeast U.S. coasts 
should monitor the latest advisories or warnings, and forecasts 
from coastal National Weather Service offices. 

.WARNINGS...Preliminary.

.NT1 New England Waters...
.ANZ900...Georges Bank east of 68W...
     Gale Possible Wednesday night.

.NT2 Mid-Atlantic Waters...
.ANZ920...Baltimore Canyon to the Great South Channel...
     Gale tonight into Monday. 
     Gale Possible Wednesday into Wednesday night. 
     Gale Possible Friday night.
.ANZ905...The Great South Channel to the Hague Line...
     Gale Possible Wednesday night.
.ANZ910...East of the Great South Channel and south of 39N...
     Gale tonight into Monday. 
     Gale Possible Wednesday into Wednesday night. 
     Gale Possible Friday night.
.ANZ825...Inner Waters from Baltimore Canyon to Cape Charles Light...
     Gale today into Monday. 
     Gale Possible Friday night.
.ANZ828...Inner Waters from Cape Charles Light to Currituck Beach Light...
     Gale today.
     Storm tonight.
     Gale Monday into Monday night. 
     Gale Possible Friday night.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras Canyon...
     Storm today into tonight. 
     Gale Monday into Monday night. 
     Storm Tuesday.
     Gale Possible Friday night.
.ANZ830...Inner Waters from Currituck Beach Light to Cape Hatteras...
     Storm today into tonight. 
     Gale Monday into Monday night. 
     Gale Possible Friday night.
.ANZ833...Inner Waters from Cape Hatteras to Cape Fear...
     Storm today into tonight. 
     Gale Monday into Monday night. 
     Gale Possible Friday night.
.ANZ930...Outer Waters from Hatteras Canyon to Cape Fear...
     Storm today into tonight. 
     Gale Monday into Monday night. 
     Storm Tuesday.
     Gale Possible Tuesday night.
     Gale Possible Friday night.
.ANZ835...Inner Waters from Cape Fear to 31N...
     Gale today into Monday. 
     Gale Possible Friday night.
.ANZ935...Outer Waters from Cape Fear to 31N...
     Gale today into Tuesday. 
     Gale Possible Friday night.

$$

.Forecaster Mills. Ocean Prediction Center.