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AGNT40 KWNM 171408

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
908 AM EST TUE JAN 17 2017

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

Weak pressure pattern prevails over the waters with OPC
preliminary 12Z surface analysis showing a weak cold front in
central NT1 waters near Cape Cod while to the south a low pressure
trough and hint of a weak low with no closed center was over the
central NT2 waters. Pressure gradients are weak and winds are

Present wind grids are based on 12Z GFS from yesterday blended
with 12Z ECMWF. With more recent runs showing little change
through Friday plan to make no changes for morning update.
Beginning Friday night 06Z GFS trended slower with a weak low
moving off the Carolina coast in progressive westerly flow versus
other models including 12Z ECMWF. For the morning update
repopulated winds with more current 00Z ECMWF as compromise for
Friday night through Saturday night with only minor resulting
changes in winds with ECMWF boundary layer winds boosted by 10
percent in northerly flow after weak low passes.

Seas...The 50/50 percent blend of the 12Z wave models appear
representative and with a similar blend preferred for winds
through Friday, no changes are planned for morning update. After
Friday transitioned to more current 00Z ECMWF WAM when winds of
that model are preferred with some minor edits.

Overall, the 00Z global models are in good agreement over the
waters for the next 3 to 5 days. The main weather feature
impacting the waters will be intensifying low pressure moving
east and southeast from near Long Island early Wednesday.

Until then high pressure currently over the region will move
southeast away from the waters today into tonight as a weakening
cold front drops southeast and south over NT1 waters. The low
will move east and southeast from near Long Island around 12Z
Wednesday to east of the northern NT2 waters, near 36N 66W, by
06Z Thursday. Fairly widespread gales appear likely over portions
of the NT2 waters into the southeastern NT1 waters Wednesday into
Thursday. High pressure will follow the low, and push east over
the region later Thursday into Friday. For Friday night into
Saturday night another low is expected to cross southern or
central NT2 waters, with high pressure building south and
southeast over the waters in the wake of the low later Saturday
and Saturday night. At this time, gale force winds appear
unlikely with the late week low pressure system. For today into
tonight we will rely on the 00Z GFS 10 meter winds over the
offshore waters, and then later tonight into Friday rely on the
00Z GFS using the smart tool which places the stronger first
sigma layer winds over unstable areas, and slightly lower 10
meter winds over stable areas. For Friday night through Saturday
night we will use an even blend of the 00Z GFS and 00Z ECMWF over
the region to account for minor differences in the guidance.
Confidence levels in the forecast are near to above average over
the next few days.

.Seas...Both the 00Z Wave Watch III and 00Z ECMWF WAM have
initialized too low over the Gulf of Maine waters where sea
heights near 9 feet or so are being detected. Elsewhere, both
models appear to have initialized quite well. For the early
morning package we will adjust the forecast and grids manually to
account for these higher seas, and then allow the seas to slowly
subside throughout the day, back toward the wave height guidance
levels by tonight. For tonight through Saturday night we will use
a 50-50 blend of the Wavewatch and WAM models, as both models are
in pretty good agreement over the region for the next 3 to 5

.Extratropical Storm Surge Guidance...N/A.


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

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


.Forecaster Bancroft/Mills. Ocean Prediction Center. is the U.S. government's official web portal to all federal, state and local government web resources and services.