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AGNT40 KWNM 212010

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
310 PM EST Tue Feb 21 2017

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

Grids: 12Z GFS throughout the forecast period, except 12Z Thu to
12Z Sat, will use a local smart tool that uses first sigma level
winds in areas that are unstable, and representative 10m winds
elsewhere. Reasoning and discussion follows.

As far as February is concerned, a rather quiet few days on the
horizon as high pressure settles over the West Atlantic through
Wednesday night, resulting in mostly calm winds and flat seas
across the bulk of OPC waters. The high will slowly shift east
of the area Thursday and Thursday night, as low pressure races
quickly east across Quebec and New Brunswick dragging a cold
front into the northern waters. The cold front should only make
it to about 40N by Friday morning, stall, then lift back north as
a warm front Friday night ahead of an approaching strong cold
front. Across the NT2 waters, southern stream closed upper low
will move across Florida Wednesday night and Thursday, lift north
and northeast across the waters Friday and Friday night, then
dissipate or become absorbed into passing cold front sweeping
across the entire area Saturday and Saturday night. After fropa,
cold air advection and high pressure will filter east across the
offshore zones Sunday and Sunday night.

Models remain in remarkably good agreement throughout most of the
forecast period, leading to high overall forecast confidence.
That being said, marginal gale headlines remain across the
southern and outer zones 930 and 935 along the north quadrant of
anomalous southern stream low early Friday afternoon. While 12Z
GFS continues to output possible gales in first sigma level
winds, only marginal support remains from non-NCEP guidance
(only 25-30 kt). But in deference to forecast continuity, will
keep gale headlines in place for now. With a slightly higher
degree of confidence, gales also remain in the forecast Saturday
night across the northern and outer zones 905 and 910 ahead of
the approaching cold front. Worth mentioning: in the cold air
advection Sunday, somewhat problematic forecast scenario arising
with respect to the strength of the offshore flow. Similar to its
previous runs the GFS remains bullish generating widespread west
to northwest gales, while non-NCEP guidance again maxes winds
25-30 kt. Being day 5 into 6, and certainly with little forecast
confidence at that time at the tail end of the forecast period,
will cap GFS winds to 32 knots and below gale threshold.

Seas: will use the 12Z WW3 into late Friday night, where
slightly higher significant wave heights are preferred as
southern stream low / possible gales lift north into the southern
waters. Will then trend forecast to a 1:1 blended solution with
the 12Z WAM to iron out the differences between the two models.
Most notably, it will trend the seas down Sunday where
operational GFS indicates possible gales that have been scrubbed
from the official grids.

.Extratropical storm surge guidance...N/A.


.NT1 New England Waters...

.NT2 Mid-Atlantic Waters...
.ANZ905...The Great South Channel to the Hague Line...
     Gale Possible Saturday night.
.ANZ910...East of the Great South Channel and south of 39N...
     Gale Possible Saturday night.
.ANZ930...Outer Waters from Hatteras Canyon to Cape Fear...
     Gale Possible Friday.
.ANZ935...Outer Waters from Cape Fear to 31N...
     Gale Possible Friday.


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