Marine Interpretation Message
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AGNT40 KWNM 271953
MIMATN

.Marine Weather Discussion for N Atlantic Ocean
.NWS Ocean Prediction Center Washington DC
345 PM EDT THU 27 JUL 2017

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

The 1430Z and 1520Z Ascat overpasses across the western portions
of the offshore waters returned highest winds to 20 kt off the
Maine coast, with winds elsewhere 15 kt or less. Over the near
term the 12Z models are in good agreement across the west
Atlantic and present no major forecast problems. Both the weak
high pressure ridge extending northeastward from near Cape
Hatteras and the weak stationary front across the waters south
of Cape Hatteras will dissipate tonight. The models are also
consistent in moving a cold front off the New England coast
early Friday. The front should stall across the NT1 waters later
Friday. Over the past several runs, the models have come into
better agreement with an amplifying upper shortwave which is
forecast to move southeast across the Great Lakes and through
the Ohio valley tonight through Friday night before closing off
near the Mid Atlantic coast Saturday and Saturday night. The
models have generally trended slower and stronger with this
system. At the surface, both the 12Z GFS and 12Z ECMWF indicate
a pair of surface lows will develop with the first moving
northeast near Georges Bank Saturday night, while the second
becomes vertically stacked and remains quasi-stationary off the
mid Atlantic coast late Saturday through Monday. The preferred
12Z ECMWF is slightly deeper than the 12Z GFS. Also, the latest
ensemble guidance suggests that the 12Z GFS may retrograde the
surface low too far southwest Sunday night/Monday. The timing
differences with how quickly the upper low along the mid
Atlantic coast will weaken this weekend and eventually lift
northeast next week have narrowed with the 12Z models. The 12Z
GFS and 12Z ECMWF are in better agreement with the low position
Monday night/Tuesday night than they are Sunday/Monday. As for
the gales, based on slower trend we had previously extended the
north to northeast gales from south of New England to off the
Delmarva further out in time (through Monday), and this still
looks reasonable. So overall the gale hazards will remain mostly
consistent. By Tue/Tue night, the 12Z models finally show the
weakening upper low will open into a trough and along with the
associated surface feature, will lift northeast.

.Seas...The 12Z Wavewatch III and 12Z ECMWF WAM were about 1 ft
low near Georges Bank, but otherwise are well initialized across
the west Atlantic this afternoon. For the forecast wave height
grids, with the 12Z ECMWF being the basis for the wind grids,
used a 4:1 12Z ECMWF to 12Z Wavewatch blend through the period.

.Extratropical Storm Surge Guidance...N/A.

.WARNINGS...Preliminary.

.NT1 New England Waters...
.ANZ810...South of New England...
     Gale Saturday.
     Gale Possible Saturday night.
.ANZ815...South of Long Island...
     Gale Saturday.
     Gale Possible Saturday night into Monday.

.NT2 Mid-Atlantic Waters...
.ANZ820...Hudson Canyon to Baltimore Canyon...
     Gale Saturday.
     Gale Possible Saturday night into Monday.
.ANZ915...Hudson Canyon to the Great South Channel...
     Gale Possible Sunday into Sunday night.
.ANZ920...Baltimore Canyon to the Great South Channel...
     Gale Saturday.
     Gale Possible Saturday night into Sunday night.
.ANZ910...East of the Great South Channel and south of 39N...
     Gale Possible Saturday night.
.ANZ825...Inner Waters from Baltimore Canyon to Cape Charles
Light...
     Gale Possible Saturday night into Sunday night.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras
Canyon...
     Gale Saturday.
     Gale Possible Saturday night into Sunday night.
.ANZ930...Outer Waters from Hatteras Canyon to Cape Fear...
     Gale Saturday.
     Gale Possible Saturday night.

$$

.Forecaster Clark. Ocean Prediction Center.



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