Marine Interpretation Message
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000
AGNT40 KWNM 050136
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
836 PM EST SUN DEC 4 2016

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

The 00z surface analysis indicated high pressure inland along the
mid Atlantic coast with ridge extending offshore across the
offshore and coastal waters. The 18z GFS/NAM were similar to the
previous 12z runs during the forecast period. The 18z GFS is
lighter with the winds with the initial low forecast to move
offshore Monday and Monday night...and with this being a weaker
outlier still prefer the 12z ECMWF. The most signficant
differences continue to be during the extended period with the
strong cold front forecast to move offshore Thursday night and
Friday with the GFS still being more progressive compared to the
other models. With all this in mind...will not be making any
significant changes to the existing grids for the evening update.
The 00z sea state analysis indicated that the ECMWF WAM values
were still more representative compared to the MWW3.

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PREVIOUS DISCUSSION...

1400Z and 1445Z Ascat overpasses confirmed that the northwest
gales have shifted east of the offshore waters and indicated 30
kt winds over the waters extending from near Georges Bank south
across the northeastern NT2 zones. The 12Z models are in good
agreement that the offshore northwest winds should continue to
diminish tonight as a high pressure ridge moves offshore. With
wind guidance in excellent agreement see no reason to deviate
from the previous grids through tonight. The 12Z models have
stayed mostly consistent with the upper level shortwave trough
along the northern Gulf of Mexico coast forecast to move
northeast to the Carolina coast tonight into Monday. The 12Z GFS
was slightly stronger with the surface winds off the mid
Atlantic coast associated with the developing low Monday...and
the 12Z GFS/ECMWF/UKMET have come into excellent agreement with
the track of the low. The previous wind grids which were based
on a 50/50 blend of the 00Z/04 and 12Z/03 ECMWF Monday and
Monday night seem a little at this time given the 12Z guidance.
So am choosing to use the 12Z ECMWF winds and will adjust these
winds upward to include some marginal gales. The 12Z 4km NAM
winds look representative in increasing the south to southwest
winds to gale across the Gulf Stream off the North Carolina
coast shortly after 12Z Monday. Given model agreement have
increasing forecast confidence with these gales...now to above
average confidence.

The models then indicate another southern stream upper shortwave
will track northeast across the mid Atlantic states Tuesday and
across the northern NT2 waters Tuesday night. Like with the
previous system the 12Z models have come into much better
agreement. Will be updating wind grids with the 12Z ECMWF which
will not result in significant changes from the previous
forecasts. As the surface low and warm front lift northeast
across the NT2 waters Tuesday and Tuesday night have about
averager forecast confidence that will see limited areas of gale
force winds. At the end of the week, models continue to show
timing differences with the highly amplified upper level trough
and attendant cold front approaching the east coast with the GFS
continuing to be more progressive than the ECMWF and UKMET. As
has been the case over the past several runs the 12Z GEFS mean
suggests the GFS is too fast. In addition models differ with the
developing surface low along the arctic cold front. We prefer
the more northern ECMWF and UKMET solutions. As the first surge
of Arctic air ushers its way offshore Friday and Friday night
will be bumping up the ECMWF winds to account for its usual low
bias  in strong cold air advection. Have well above average with
offshore gales becoming widspread across the waters from near
Hatteras Canyon northward given the steep low level lapse rates.

.Seas...Across the Georges Bank and the northern outer NT2
waters, significant wave heights continue about 1 to 3 feet
higher than the 12Z Wavewatch III this afternoon. The higher 12Z
ECMWF WAM is much better initialized with the west Atlantic wave
heights. With the general preference for the ECMWF winds through
the forecast period, will be using a 75% 12Z ECMWF WAM and 25%
12Z WW3 blend through Thursday. Thursday night through the end
of the period blended about 10% of the 12Z WW3 with the 12Z
ECMWF WAM to slightly tone down the latter`s wave heights which
reached about 24 feet across the northern outer NT2 waters
Friday night.

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

.WARNINGS...Preliminary.

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

.NT2 Mid-Atlantic Waters...
.ANZ820...Hudson Canyon to Baltimore Canyon...
     Gale Possible Friday into Friday night.
.ANZ915...Hudson Canyon to the Great South Channel...
     Gale Possible Friday night.
.ANZ920...Baltimore Canyon to the Great South Channel...
     Gale Monday into Monday night.
     Gale Possible Friday into Friday night.
.ANZ905...The Great South Channel to the Hague Line...
     Gale Monday night.
     Gale Possible Friday night.
.ANZ910...East of the Great South Channel and south of 39N...
     Gale Monday night.
     Gale Possible Friday night.
.ANZ825...Inner Waters from Baltimore Canyon to Cape Charles Light...
     Gale Possible Friday into Friday night.
.ANZ828...Inner Waters from Cape Charles Light to Currituck Beach Light...
     Gale Possible Friday night.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras Canyon...
     Gale Monday into Monday night.
     Gale Possible Tuesday night.
     Gale Possible Friday into Friday night.
.ANZ830...Inner Waters from Currituck Beach Light to Cape Hatteras...
     Gale Monday.
     Gale Possible Tuesday night.
     Gale Possible Friday night.
.ANZ833...Inner Waters from Cape Hatteras to Cape Fear...
     Gale Monday.
     Gale Tuesday.
     Gale Possible Friday night.
.ANZ930...Outer Waters from Hatteras Canyon to Cape Fear...
     Gale Monday.
     Gale Possible Tuesday night.
     Gale Possible Friday into Friday night.
.ANZ835...Inner Waters from Cape Fear to 31N...
     Gale Tuesday.
.ANZ935...Outer Waters from Cape Fear to 31N...
     Gale Tuesday.
     Gale Possible Tuesday night.

$$

.Forecaster Kosier/Clark. Ocean Prediction Center.



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