896
AGNT40 KWNM 160203
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
1003 PM EDT Mon Oct 15 2018

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

At this time I don`t plan on making any changes to the current
grids or associated text forecasts. The most recent ASCAT pass is
just entering the offshore waters and indicates SW winds 20-30
kt at 00Z.

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PREVIOUS DISCUSSION...

The 18Z NCEP/OPC surface analysis shows a deepening occluded low
pressure system over Quebec with its associated warm front
extending across the NT1 waters. Earlier 15Z ASCAT data supported
southwest winds of 20 to 25 kt along the northern Mid-Atlantic
coast in the warm sector ahead of the approaching cold front.
Further south, a weakening high pressure ridge persists across
the southern NT2 zones.

A series of strong cold fronts moving across the region will
result in several gale events over the next five days. The first
front will cross the New England and northern Mid-Atlantic waters
tonight into early Tue. The 12Z guidance consistently depicts
925 mb winds of 50 to 60 kt ahead of the front with gale force
surface winds supported by the global models as well as the 12Z
NAM Nest and WRF-ARW winds. We will use the 12Z ARW winds with
high confidence tonight through Tue night with slight edits for
warning continuity. Stronger winds and higher seas can be
expected near thunderstorms that develop along the front.

The next front will cross the northern waters Wed night into Thu.
Again, the 12Z GFS/ECMWF/UKMET/CMC all support post-frontal
northwesterly gales. Additionally, there is general model agreement
that low pressure will track across the central NT2 waters Wed,
with most models besides the ECMWF keeping associated winds just
below gale force over the offshore zones. For this time period
(Wed through Thu night), we will transition the wind grids to the
12Z GFS and use a tool to populate with first sigma level winds
in areas where the lapse rates support deeper boundary layer
mixing. This maintains gales across much of our NT1 and far outer
NT2 waters Wed night into Thu.

The final frontal system will move off the Atlantic coast late
Sat through Sat night. Even at day five, the 12Z global models
consistently highlight the potential for gales ahead of the cold
front, particularly across the far outer NT2 zones on Sat night.
We favor the more conservative 12Z ECMWF winds Fri through Sat
night, which still includes marginal gales for ANZ905/910 by the
end of the period. This portion of the forecast will likely be
refined in the coming days, but the model signal is strong
enough to warrant including gales even in the extended period.


.SEAS...Few changes were made to the near term wave grids as they
matched up well with the preferred 12Z ARW winds through Tue night.
For Wed through Thu night, we favored a blend of the 12Z Wavewatch
and ECMWF WAM seas to boost the slightly lower Wavewatch while
maintaining continuity with our wind forecast. Then, the wave
grids were transitioned to the 12Z WAM seas Fri through Sat night
to match our more conservative wind forecast.


.EXTRATROPICAL STORM SURGE GUIDANCE...No significant positive
surge events are expected over the next several days.



.WARNINGS...Preliminary.

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

.NT2 Mid-Atlantic Waters...
.ANZ820...Hudson Canyon to Baltimore Canyon...
Gale tonight.
.ANZ915...Hudson Canyon to the Great South Channel...
Gale tonight.
.ANZ920...Baltimore Canyon to the Great South Channel...
Gale tonight into Tuesday.
.ANZ905...The Great South Channel to the Hague Line...
Gale tonight into Tuesday.
Gale Possible Wednesday night into Thursday night.
Gale Possible Saturday night.
.ANZ910...East of the Great South Channel and south of 39N...
Gale tonight into Tuesday.
Gale Possible Wednesday night into Thursday.
Gale Possible Saturday night.

$$

.Forecaster Shaw/Reinhart. Ocean Prediction Center.