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AGNT40 KWNM 152017
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
315 PM EST SUN 15 DEC 2019

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

Ascat overpasses from 1415z to 1440z showed widespread gale
force winds generally north of Baltimore Canyon and east of
72.5W which matched up quite well with the OPC wind grids. The
12z models, even including the high resolution guidance, did not
show gales extending as far west as the Ascat this morning. The
12z GFS first sigma level winds were probably the best
initialized. The latest guidance remained consistent with these
west to northwest gales persisting across the offshore waters
north of Baltimore Canyon today, and then beginning to diminish
from southwest to northeast over the aforementioned area tonight
into early Mon. We will not make changes to the previous wind
grids, which were based on a blend of the GFS first sigma level
winds and the ECMWF surface winds, through early Mon. The 12z
models then continued to offer some minor differences with the
track and timing of the developing surface low expected to move
east across the New England waters Tue into Tue night. The 12z
ECMWF and 12z UKMET were mostly consistent with their respective
previous runs, and are a few millibars weaker and slightly south
of 12z GFS. Despite these differences, the models are generally
consistent that gale force winds will again develop across the
outer NT2 zones north of Hatteras Canyon ahead of the front Tue
into Tue night. The southwest gales will shift east of the
offshore waters early Wed morning. Wind grids are based on a
blend of the 12z ECMWF bias corrected winds and the 12z GFS Mon
through Tue night. Our confidence is well above average with
these gale hazards.

The models are then consistent in moving another surface low off
the Maine coast and over the Gulf of Maine late Wed and Wed
night with a reinforcing arctic cold front passing southeast
across the waters Wed night and Thu. The 12z GFS trended back
toward the consistent ECMWF, and again shows a more rapid
deepening of the low east of the New England waters, and as a
result stronger northwest winds across the offshore waters.
These winds were adjusted higher, now up to 45 kt over Georges
Bank and the northern NT2 waters late Wed night and early Thu.
Given the strength of the cold air advection and the way the
models have recently underperformed in these cases, would not be
surprised if storm force winds are added across these outer
zones in subsequent forecasts over the next couple days. Once
the hazards shift east of the offshore waters by early Fri
morning, conditions should finally improve Fri into the weekend
as high pressure moves to the Mid-Atlantic coast. The same blend
of the 12z ECMWF bias corrected winds and 12z GFS 10m winds was
used for the wind grids Wed through Fri night. Forecast
confidence through the end of the week is above average.

.Seas: Both the 12z Wavewatch and 12z ECMWF WAM are up to 2 ft
or so too low with the wave heights over Georges Bank and the
northeastern NT2 waters this afternoon. Across the offshore
waters, the 12z WW3 and 12z WAM are in good agreement through
Mon night. Then with the GFS stronger with the first developing
low and associated winds late Tue and Tue night, WW3 is then
higher than the WAM with the associated wave heights. Similar to
what was done with the winds, we will use an even blend of the
above guidance through Wed. For tonight, we adjusted the higher
seas upward by 15 percent or so to better match the latest buoy
observations. We then prefer the higher ECMWF WAM for the seas
associated with the arctic frontal passage Wed night through the
end of the week. Therefore, will use a 3:1 blend of the ECMWF
WAM and Wavewatch during that time.

.Extratropical Storm Surge Guidance...With mainly an offshore
flow regime expected for the next several days, significant
positive surge is not expected through the end of the week.
Please consult forecasts and products your local National
Weather Service office for more information.

.WARNINGS...Preliminary.

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

.NT2 Mid-Atlantic Waters...
.ANZ820...Hudson Canyon to Baltimore Canyon...
Gale Possible Wednesday night into Thursday.
.ANZ915...Hudson Canyon to the Great South Channel...
Gale today into tonight.
Gale Tuesday.
Gale Possible Wednesday night into Thursday.
.ANZ920...Baltimore Canyon to the Great South Channel...
Gale Tuesday.
Gale Possible Tuesday night.
Gale Possible Wednesday night into Thursday.
.ANZ905...The Great South Channel to the Hague Line...
Gale today into tonight.
Gale Tuesday.
Gale Possible Tuesday night.
Gale Possible Wednesday night into Thursday night.
.ANZ910...East of the Great South Channel and south of 39N...
Gale today into tonight.
Gale Tuesday.
Gale Possible Tuesday night.
Gale Possible Wednesday night into Thursday night.
.ANZ825...Inner Waters from Baltimore Canyon to Cape Charles
Light...
Gale Possible Wednesday night into Thursday.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras
Canyon...
Gale Tuesday.
Gale Possible Tuesday night.
Gale Possible Wednesday night into Thursday.

$$

.Forecaster Clark. Ocean Prediction Center.