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740
AGNT40 KWNM 180758
MIMATN

.Marine Weather Discussion for N Atlantic Ocean
.NWS Ocean Prediction Center Washington DC
245 AM EST WED 18 JAN 2017

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

The most recent Ascat overpasses missed areas across the central
NT2 waters where the highest west to southwest winds are
occurring. The 01Z and 02Z passes did return east to southeast
winds to 20 kt extending from Cape Cod across Georges Bank. The
latest models are in very good agreement across the west
Atlantic for the next few days. Forecast confidence remains well
above average with the gales to develop today and tonight as the
upper level low currently over the Ohio valley moves eastward
toward the mid Atlantic coast and across the NT2 waters. At the
surface, the main weather features impacting the waters will be
the associated intensifying low pressure forming as a secondary
or triple point low early today, while the primary low center
dissipates over northeast New York state. This low then tracks
east and southeast from the southern NT1 waters today into
Thursday while intensifying east of the offshore waters. Fairly
widespread gales appear likely over portions of the NT2 waters
into the far southeastern NT1 waters today into early Thursday.
For wind grids through Thursday night, will be using the 00Z
GFS, except across the areas with negative low level lapse
rates, will be using the higher GFS first sigma level winds.

As the strong low then accelerates northeast Thursday and
Thursday night, a north to south oriented high pressure ridge
will move east off the coast, and across the waters Friday and
Friday night. The 00Z models all show a number of weak upper
level impulses will move off the southeast coast Friday into
Friday night. Although the models differ with the details of the
timing and positions of the associated surface lows, they are
consistent that each of these features will be weak as they
slowly drift east across the NT2 waters. Through Saturday
continued to use the 00Z GFS for wind grids. Thereafter the 00Z
models all forecast a closed mid and upper level low will track
eastward across the southeast US. The 00Z GFS/UKMET/ECMWF/CMC
are all in above average agreement at days 5 and 6. The main
differences are with the timing of the warm front lifting north
through the offshore waters as well as with the approaching cold
front. We prefer the slightly more progressive ECMWF and UKMET
which are better supported by the lastest ensemble guidance. So
beginning Saturday night, will transition to the 00Z ECMWF for
wind grids. Given model agreement have slightly above average
forecast confidence that gales will develop Sunday and Sunday
night both north and south of the warm front. Given the tendency
of the ECMWF`s winds to be underdone in easterly flow, did boost
the winds north of the warm front by about 10 percent Sunday
night.

.Seas...Although the 00Z ECMWF WAM appears to have a better
handle on the west Atlantic wave heights than the 00Z Wavewatch,
the former is slightly high. An 80% 00Z ECMWF WAM/20% 00Z
Wavewatch blend seemed to match the latest observations best.
Used this blend through Thursday, then a 50/50 blend Thursday
night through Saturday. Then given preference for the ECMWF in
the medium range, reverted back the the 80/20 blend from
Saturday night onward.

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

.WARNINGS...Preliminary.

.NT1 New England Waters...
.ANZ805...Georges Bank west of 68W...
     Gale today into tonight.
.ANZ900...Georges Bank east of 68W...
     Gale today into tonight.
.ANZ810...South of New England...
     Gale Possible Sunday night.
.ANZ815...South of Long Island...
     Gale Possible Sunday night.

.NT2 Mid-Atlantic Waters...
.ANZ820...Hudson Canyon to Baltimore Canyon...
     Gale Possible Sunday night.
.ANZ915...Hudson Canyon to the Great South Channel...
     Gale Possible Sunday night.
.ANZ920...Baltimore Canyon to the Great South Channel...
     Gale tonight.
     Gale Possible Sunday night.
.ANZ905...The Great South Channel to the Hague Line...
     Gale today into tonight.
.ANZ910...East of the Great South Channel and south of 39N...
     Gale tonight into Thursday.
     Gale Possible Sunday night.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras
Canyon...
     Gale today into tonight.
     Gale Possible Sunday night.
.ANZ830...Inner Waters from Currituck Beach Light to Cape
Hatteras...
     Gale today.
     Gale Possible Sunday night.
.ANZ833...Inner Waters from Cape Hatteras to Cape Fear...
     Gale today.
     Gale Possible Sunday night.
.ANZ930...Outer Waters from Hatteras Canyon to Cape Fear...
     Gale today into tonight.
     Gale Possible Sunday night.
.ANZ835...Inner Waters from Cape Fear to 31N...
     Gale today.
     Gale Possible Sunday into Sunday night.
.ANZ935...Outer Waters from Cape Fear to 31N...
     Gale today into tonight.
     Gale Possible Sunday into Sunday night.

$$

.Forecaster Clark. Ocean Prediction Center.



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