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000
AGNT40 KWNM 201200
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
700 AM EST FRI JAN 20 2017

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

As a high pressure ridge continues to build offshore, generally
light (primarily 10-15 kt, or less) winds have developed
throughout all of the coastal/offshore waters. Highest seas
through the waters are in the 7-9 ft range, highest across the far
SE NT1 and NE most NT2 waters, which are being handled slightly
better by the higher 00Z ECMWF WAM versus the 06Z Wavewatch III at
the moment.

Over the short term, the latest models present no major forecast
problems. Would favor the similar 06Z/00Z GFS and 00Z ECMWF
solutions of a very weak surface low developing off the N Carolina
coast late today, tracking E across the central NT2 waters
tonight, then passing E of the waters Sat. So other than making
some minor tweaks in deference to the 00Z ECMWF, will not make any
other significant short term changes to the previously populated
winds.

In the long range, the latest models in general agree that a
nor`easter will develop off the mid Atlantic coast by late Mon/Mon
night, then track NE across the NT1 waters Tue/Tue night. Versus
its previous 00Z run, the 06Z GFS has now trended both more
progressive and further NW with the forecast track of its surface
low. The 06Z GEFS Mean though, especially by Tue/Tue night,
indicates that the 06Z GFS forecast track may be too far NW. But
overall the 06Z GFS forecast gradients associated with this system
are similar to those forecast by the 00Z GFS/ECMWF.  Therefore
overall would favor a compromise 06Z/00Z GFS and 00Z ECMWF
solution for this system. The previous forecast package used the
previous official winds grids (12Z GFS/ECMWF blend) with
additional edits in deference to the 00Z GFS/ECMWF, which still
does not look unreasonable. So for now for the next offshore
forecast package will continue to use these official grids and
will just make some additional further edits in deference to the
06Z GFS and 00Z ECMWF.




-----------------------------------------------------------------
PREVIOUS DISCUSSION...

The 01Z and 02Z Ascat overpasses still indicated north winds to
25 kt across the outer northern NT2 waters last evening, but
across the inner offshore zones winds were 15 kt or less. As the
weak high pressure ridge continues to drift eastward across the
NT1 and NT2 waters, winds should become 15 kt or less across all
the offshore zones today. The 00Z models all move a weak upper
shortwave along the mid Atlantic coast today and offshore
tonight, with an associated weak surface low passing east off
the coast just north of Cape Hatteras late this afternoon and
across the waters tonight into early Saturday. Both the 00Z
ECMWF and 00Z GFS indicate there could be a brief period where
winds within the immediate vincinity of the low could reach 25
kt tonight. For wind grids through Saturday night, maintained
continuity and used the 00Z GFS 10m winds, except where unstable
populated with the slightly higher 00Z GFS first sigma level
winds.

The main weather feature impacting the offshore waters this
forecast period will be the upper level low forecast to track
eastward across the southeast US Sunday night, then along the
mid Atlantic coast Monday into Monday night, and New England
coast Tuesday and Tuesday night. The latest models are generally
in pretty good agreement but differences lie in the details
including the timing of both the coastal low as well as the warm
front lifting north across the offshore waters. Over the past
few days, the GFS has been consistently slower than the
ECMWF/UKMET/ Canadian in lifting the warm front north across the
waters Sunday into Tuesday. The 00Z GFS, 00Z ECMWF, and 00Z
UKMET are all in much better agreement with the 00Z Canadian
slower than the above consensus. As the surface low approaches
the New England coast and the NT1 waters early Tuesday, the 00Z
GFS became an eastern outlier, with the 00Z ECMWF and 00Z UKMET
probably in the best agreement of the deterministic models. Over
the past several runs, the ECMWF has been incredibly consistent
with this system. The latest GEFS mean and ECMWF EPS mean lie
between the eastern GFS and western consensus. After taking all
the 00Z guidane into consideration, do not see any compelling
reasons to deviate from the previous OPC winds grids, which were
based on a 12Z/19 GFS and 12Z/19 ECMWF blend. The only slight
modification we will make to the previous grids will be to
increase the easterly winds (by 10 percent or so) across the
northern NT2 and NT1 waters Sunday night through Monday night.
This is based on the stronger trend seen in both the GFS and
ECMWF, as well as these models tendency to be underdone in these
easterly flow scenarios. Gale headlines will remain unchanged
from the previous NT1/NT2 forecasts.

.Seas...The higher 00Z ECMWF WAM has initialized the current
seas better than the lower 00Z Wavewatch III. Therefore will
populate the wave grids with the 00Z ECMWF WAM today, then will
use a 50/50 blend of the above guidance tonight through Saturday
night. Since there were not any significant changes made to the
previous wind grids Sunday through Tuesday night, will maintain
the previous wave height grids as well, which were a 50/50 blend
of the 12Z/19 Wavewatch III and 12Z/19 ECMWF WAM.

.Extratropical Storm Surge Guidance...In the strong easterly
gradient forecast to develop N of the warm front and migrate
northward along the coast Sunday night into early Tuesday, the
00Z ESTOFS forecasts a more significant surge (up to 3-4+ ft) to
develop along the coast from Delaware to Long Island Sound than
forecast by the 12Z ETSS. Given the relatively slow movement of
the front and the stronger trend seen in the GFS and ECMWF noted
above, believe the higher ESTOFS values are more reasonable, and
could perhaps be somewhat underdone. Highest surge should occur
Monday night from the New Jersey coast to Long Island, with the
ESTOFS indicating 4+ ft within Long Island Sound.


.WARNINGS...Preliminary.

.NT1 New England Waters...
.ANZ800...Gulf of Maine...
     Gale Possible Monday into Tuesday.
.ANZ805...Georges Bank west of 68W...
     Gale Possible Sunday night into Monday night.
.ANZ900...Georges Bank east of 68W...
     Gale Possible Sunday night into Monday night.
.ANZ810...South of New England...
     Gale Possible Sunday night into Monday night.
.ANZ815...South of Long Island...
     Gale Possible Sunday night into Monday night.

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

$$

.Forecaster Vukits/Clark. Ocean Prediction Center.



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