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AGNT40 KWNM 090025

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
725 PM 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.

An arctic cold front is now moving offshore across the NT1 and
nrn/central NT2 waters with maximum postfrontal winds generally in
the 20-30 kt range. Seas associated with this fropa have just
begun to build and are now only in the 4-7 ft range which are in
between what is being forecast by the 18Z Wavewatch III and 12Z
ECMWF WAM models at the moment.

Over the short term...The 18Z NAM/GFS just confirm the previously
forecasted trends of their respective 12Z runs and are in very
good agreement with the other 12Z global models in forecasting the
cold front to pass SE of the NT2 waters tonight...followed by
strong high pressure building in from the W Friday/Friday night
while a series of surface trofs pass SE across the NT1 and Nrn NT2
waters causing a strong WNW gradient to pulsate with marginal gale
force winds. Therefore will continue to use the previously
populated winds...but in deference to the 18Z GFS and 12Z ECMWF
forecasting a final upper short wave trof to pass offshore causing
the gradient to re-tighten late Saturday/early Saturday night will
add gales to NT2 zone ANZ905. So otherwise no significant short
term changes are planned to the previous offshore forecasts.

In the long range...The 18Z GFS continues the trend of its
previous 12Z run of forecasting a much more amplified upper level
pattern late Monday into Tuesday with a closed upper low
supporting a strong surface low passing just N of the area Monday
night while pulling a strong cold front offshore with widespread
associated gale force boundary layer winds. The 18Z GEFS Mean
supports this strong GFS solution. The problem is that every other
12Z global model forecasts a significantly less amplified upper
level pattern with a warm front developing off the mid Atlantic
coast Sunday night...followed by a developing surface low moving
offshore along this front Monday...followed by the low then
passing E of the offshore waters Monday night while pulling the
front back S as a cold front into Tuesday. The previous forecast
package used a blend of the 00Z GFS/ECMWF for this system. So
since its similar to this blend and in good agreement with the
latest WPC Medium Range guidance...will now go ahead and
repopulate our forecast grids with the 12Z ECMWF boundary layer
winds and its associated 12Z ECMWF WAM seas for Monday through
Tuesday night which overall will result in no major changes to
the previously forecasted associated possible gale warnings.


At 18Z a 1005 mb low was east of the NT1 and northern NT2 waters
with a cold front extending back into the central NT2
waters...connecting to a 1015 mb low at 34n73w with a cold front
extending south from that low into the southern NT2 waters. A 1502Z
ASCAT hires pass revealed 20-25 kt winds over the southeast NT1
and northeast NT2 waters with 10-20 kt winds over the remainder of
the NT1 waters and roughly the same for the NT2 waters...except
over the inner waters off the DelMarVa peninsula.

12z guidance was in good agreement through Sun with continued
divergent solutions from Sun night on. Hence populated grids
through 09/12z with new 12Z GFS 30m winds...then left previous
grids in for the rest of the forecast period. This was done given
agreement in the 12Z guidance in the short term...then desire to
not adjust forecast in the long term given the continued divergent
model solutions and the preference to await future model trends.
NW flow regime continues through Sun in the wake of low
pres...currently near 34n73w...that will rapidly deepen as it
moves northeast across Nova Scotia and eventually to a position
south of Greenland by late Sat. Will continue with mention of
gales Fri night over parts of the NT1 and northern NT2 waters as
the NW flow continues. Guidance agrees on a strong low moving into
New England then either across the NT1 waters or just to the
north Mon into Tue. As mentioned in the 06z/12z discussions
model solutions remain divergent from Sun night on in regards to
the timing of the strong low pres expected to move across New
England and its associated warm and cold front. Hence decision to
continue with ongoing grids in the forecast which results in
continued mention of gales Mon into Mon night in association with
the low.

.SEAS...Continued with the higher 12Z ECMWF WAM model through
09/12z...leaving in prior wave grids beyond that time given choice
to maintain ongoing wind grids in the forecast beyond 09/12z also.

forecast a slightly more significant negative surge developing
tonight in the nw gradient along the coast from Long Island Sound
to Delaware Bay...persisting 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.
     Gale Possible Monday into Monday 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 Saturday.
     Gale Possible Saturday night.
     Gale Possible Monday into Tuesday.
.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 Vukits/Holley. Ocean Prediction Center. is the U.S. government's official web portal to all federal, state and local government web resources and services.