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AGNT40 KWNM 201955
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
355 PM EDT Tue Apr 20 2021

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

Low pressure will likely develop along a stationary front off the
E coast of Florida overnight, then track NE while clipping the
outer and far southern OPC offshore waters. Some of the 12z
guidance has shifted the track of the low more to the NW, and the
near term grids will updated with the ECMWF to reflect this
trend. While there are gale force winds present in the model -
and other NW tracks like the NAM - expect these are more an
artifact of convective feedback within thunderstorms. Regardless,
it serves a good reminder that any convection will likely be
accompanied by locally very gusty winds and rough seas. Will
increase the grids to reflect sustained 30 kt overnight in these
far SE zones.

Wed into Sat: models continue in excellent agreement a strong
cold front will approach the coast Wed. The front will slide E
over the waters later Wed into Wed night, clearing E of the area
by early Thu. An associated intensifying low pressure area will
track from West Virginia late tonight to coastal Maine by Wed
night, with the low lifting N into the Canadian Maritimes Thu and
Thu night into Fri. A secondary strong cold front will cross the
New England and northern Mid-Atlantic waters Thu and Thu night,
with a series of low pressure troughs crossing the New England
waters Fri into Fri night as high pressure slides E off the
Carolina coast. To update some of the timing and spatial extent
of the expected hazard winds, will 1:3 blend the latest 12z GFS
winds, adjusted for stability, with the ongoing forecast. With
500 hPa height anomalies approaching 5 standard deviations below
normal, and given the remarkable consistency among the models,
confidence in the long duration gale event is well above average.

Sat into next week: Models are also converging on similar
solutions that an already deep low pressure will track to the
Delmarva late Sat night, move NE along the coast into the Gulf
of Maine by Sun night (potentially into the low to mid 980 hPa),
then slowly move E of the area passing south of Nova Scotia Mon
into Tue. Again with increasing consistency in the models, even
at this range, will continue carrying hazards at this tail end of
the medium range. In fact, plan to extend the coverage of gale
headlines to include most of the NT2 waters. By this time
tomorrow, would not be surprised to see warnings further expanded
to include all of NT1, but would prefer to slowly step toward
that wide of coverage for the time being. From about 18z Sat
into 12z Mon will run a blend of the 12z GFS, 12z ECMWF, and 00z
ECMWF. From 12z Mon onwards, will run an even blend of the 12z
GFS and 00z ECMWF where the latest 12z ECMWF stalls the low
across the Gulf of Maine (not supported in ensembles). No edits
were made along the Gulf Stream, but as we draw nearer to the
event, likely to see winds expanded and increased as our
confidence level rises. All mariners should closely monitor the
latest OPC forecast.

Seas: Both 12z wave models continue to initialize seas fine this
afternoon, however will lean closer to the WAM where the ECMWF
is preferred over the next 12 to 24 hours. Will then blend the
latest 12z WaveWatch into the ongoing grids this weekend, however
will increase seas in gales as much as 15 percent where there is
an expectation of maximum values being washed out in the blends.
At the end of the medium range, will follow the same blend as the
winds mentioned above, however again boosting seas during
forecast gales.

Extratropical Storm Surge Guidance: No significant positive
surge events are expected during the next several days. Please
monitor products from coastal National Weather Service offices
for detailed water level information.

.WARNINGS...Preliminary.

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

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

$$

.Forecaster Collins. Ocean Prediction Center.