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AGNT40 KWNM 081305

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
805 AM EST THU DEC 8 2016

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

At 12z a 1010 mb low was over the far northeast NT2 waters with a
cold front extending south to southwest from its center down into
the southern NT2 waters. With the 06z GFS/NAM in good agreement
over the short term see no reason to make changes to the ongoing
forecast in place. Current warning headlines will remain as is for
this intermediate update.


Over the short term...Overall the new 00Z models remain in
reasonably good agreement and share similar forecast timing for
an arctic cold front to push offshore today...then pass SE of the
offshore waters tonight with a strengthening NWly gradient
developing throughout the waters. Then Friday into Friday night as
a strong high pressure ridge is forecast to build in from the
W...and in response to an upper short wave trough forecast to pass
across the nrn waters...the 00Z GFS continues to forecast the
associated cold air advection and negative static stability to max
out which in turn will cause the NWly gradient to strengthen to
marginal gale force across the NT1 and nrn NT2 waters. Overall
would favor the slightly stronger 00Z NAM/GFS/GEM solutions for
this gradient. Therefore similar to the previous forecast
package...plan on populating our forecast wind grids with the
somewhat stronger 00Z GFS first sigma level winds for today
through Saturday night...with some minor additional edits mainly
in deference to the 00Z NAM/ECMWF. So as a result anticipate
making only minor changes to the previously forecasted
moderate/high confidence gales associated with this gradient.

In the long range...The 00Z models continue to be in good
agreement that a high pressure ridge will build towards the east
coast Saturday night...then move offshore Sunday causing the NWly
gradient to gradually weaken with winds diminishing from W to E.
Then Sunday night into Monday night the disparity between the 00Z
global models increases significantly. Though more progressive
than its previous 18Z run...the 00Z GFS continues to forecast a
warm front to develop off the mid Atlantic coast Sunday night...
followed by a developing low racing E along the front across the
Nrn NT2 waters Monday...then passing off to the E Monday night
while pulling the front back s across the NT2 waters as a cold
front. Though there are a lack of associated individual ensemble
members...if anything the 00Z GEFS indicates the 00Z GFS solution
may be too progressive with this system. On the other hand the 00Z
GEM forecasts a much more amplified upper level pattern with a
strong associated surface low tracking into the eastern great
lakes Monday while pulling a strong warm front NE across the Nrn
waters...followed by the low passing across the Nrn NT1 waters
Monday night while pulling a strong cold front offshore...which is
similar to the old 12Z ECMWF solution. The 00Z UKMET solution
looks like a too progressive outlier solution during this time
period. Surprisingly the 00Z ECMWF has now come in much less
amplified than its previous 12Z run and is now in much better
agreement with the 00Z GFS...though slightly less progressive.
Therefore as a compromise will populate with our smart tool that
will place stronger 00Z GFS first sigma level winds in unstable
areas and weaker 00Z GFS 10m boundary layer winds in stable areas
for Sunday through Monday night. Then as a compromise...will time
shift these winds 6 hours slower Monday/Monday night...and then
will blend them 50/50 with the 00Z ECMWF boundary layer winds. So
as a result of this blended compromise...will continue to forecast
possible gales to develop Monday/Monday night like the previous
offshore forecast package...but now will limit these gales to the
outermost central/Nrn NT2 waters.

.Seas...The somewhat higher 00Z ECMWF WAM model has initialized
better than the 00Z Wavewatch III. With this in mind...and
bearing in mind the Wavewatch III low bias in strong cold air
advection scenarios...will populate our forecast wave grids with
the higher 00Z ECMWF WAM model for today through Saturday night.
Then as their forecast differences narrow and since a GFS/ECMWF
compromise will be used...will then transition to populating with
a 50/50 blend of the 00Z Wavewatch III (with the same 6 hour time
shift slower on Monday/Monday night) and the 00Z ECMWF WAM for
Sunday through Monday night..

.Extratropical Storm Surge Guidance...In the strong NW gradient
forecast to develop tonight...the 00Z ESTOFS forecasts a slightly
more significant negative surge to develop along the coast from
Long Island Sound to Delaware Bay and persist into Saturday than
forecast by the 00Z ETSS. The ESTOFS is likely overdoing this
surge and would instead favor a compromise between the two models.


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

.NT2 Mid-Atlantic Waters...
.ANZ820...Hudson Canyon to Baltimore Canyon...
     Gale Friday into Friday night.
.ANZ915...Hudson Canyon to the Great South Channel...
     Gale Friday into Friday night.
.ANZ920...Baltimore Canyon to the Great South Channel...
     Gale Friday into Friday night.
     Gale Possible Monday into Monday night.
.ANZ905...The Great South Channel to the Hague Line...
     Gale Friday into Friday night.
.ANZ910...East of the Great South Channel and south of 39N...
     Gale Friday into Friday night.
     Gale Possible Monday into Monday night.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras Canyon...
     Gale Possible Monday into Monday night.


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