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000
AGNT40 KWNM 210139
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
839 PM EST FRI JAN 20 2017

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

No major changes to the ongoing OPC forecast appear necessary this
evening. Weak low pressure just east of Cape Hatteras this evening
will move east over the central NT2 waters tonight and move east
of the area Saturday. Weak high pressure over NT1 waters will
slide off to the southeast and east of the waters by tomorrow. A
more significant low pressures system is still likely to impact
the region beginning Saturday night and Sunday and persisting into
Tuesday night, with widespread gales likely over most of the
offshore zones. There remains the potential for storm force winds
developing with this low early next week. For now, we will pretty
much stay the course, and then more fully evaluate a few suite of
00Z models once they arrive later this evening.

Seas...We will make some adjustment to the ongoing forecast
initially, especially over the Gulf of Maine where the latest
observations show sea heights up to 7 feet occurring. Otherwise,
we do not plan on making significant changes to the previous OPC
forecast for the evening update.

-----------------------------------------------------------------
PREVIOUS DISCUSSION...

Over the short term, the new 12Z models remain in good agreement
that in response to a weak negatively tilted upper short wave
trough moving offshore, a weak associated surface low will develop
and pass E across the central NT2 waters tonight into early Sat.
Overall would favor the consistent and representative 12Z GFS
solution for this low and will continue to forecast max winds up
to 20 or 25 kt in its immediate vicinity.

Then the 12Z models, with generally minor timing differences all
forecast a warm front to develop off the mid Atlantic coast Sat
night, then drift slowly N across the central and Nrn NT2 waters
Sun/Sun night with strengthening SSW and Ely gradients forecast to
develop S and N of the front, respectively. The 12Z GEM looks a
little too progressive with this warm fropa, so would instead
favor a compromise 12Z GFS/UKMET/ECMWF solution on Sat night
through Sun night. Therefore through the short term, plan on
populating our forecast winds grids with the representative 12Z
GFS 10m/first sigma level winds (with our smart tool placing 10m
winds in stable areas and first sigma level winds in unstable
areas) for tonight through Sun night with additional minor edits
in deference to the 12Z UKMET/ECMWF.

In the long range, the 12Z models continue to differ in their
forecast tracks for an associated attendant surface low (a
nor`easter) to move towards the mid Atlantic coast Monday/Monday
night. But, by Tue morning the models generally agree that this
low will move to a position S of Long Island and then track NEwd
across the remaining NT1 waters later Tue/Tue night. Even though
the models differ on the track of this low, they share similar
timing for the associated front forecast to bow ahead with
similarly strong gradients. Overall would favor a compromise 12Z
GFS/UKMET/ECMWF solution for this system. Therefore on Mon into
Tue night, as a compromise will populate with a 33/33/33 blend of
the 12Z GFS 10m/first sigma and 12Z UKMET/ECMWF boundary layer
winds. Then Wed/Wed night, would favor a compromise 12Z GFS/ECMWF
solution, which looks like a reasonable compromise between the
more progressive 12Z UKMET and slower 12Z GEM, for the next cold
front to approach from the NW causing a strengthening WSW gradient
to develop. Therefore will transition to populating with a 50/50
blend of the 12Z GFS 10m/first sigma and 12Z ECMWF boundary layer
winds on Wed/Wed night.

.Seas...The 12Z Wavewatch III and 12Z ECMWF WAM have both
initialized the current seas equally well. With this in mind, and
with their associated 12Z GFS/ECMWF solutions being similar, will
populate our forecast wave grids with a 50/50 blend of the 12Z
Wavewatch III and 12Z ECMWF WAM for today through Wed night.

.Extratropical Storm Surge Guidance...In the strong Ely gradient
forecast to develop N of the front Sun night into Tue the
12Z ESTOFS forecasts a slightly more significant surge
(up to 3-4 ft) to develop Nwd up the coast from Delaware to the
SW New England coasts than forecast by the 12Z ETSS. Would
recommend favoring the higher 12Z ESTOFS solution.


.WARNINGS...Preliminary.

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

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

$$

.Forecaster Mills/Vukits. Ocean Prediction Center.


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