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000
AGNT40 KWNM 290729
MIMATN

.Marine Weather Discussion for N Atlantic Ocean
.NWS Ocean Prediction Center Washington DC
315 AM EDT Wed 29 Mar 2017

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

The 01Z and 0245Z Ascat overpasses across the offshore waters
returned some 25 kt winds east of the cold front, across the
Gulf Stream over the inner waters southeast of Cape Lookout as
well as the northern outer NT2 waters. However, Met-op A and B
missed most of the Gulf Stream from east of Cape Hatteras to
about 72W.
The 00Z models, namely the 00Z GFS and 00Z ECMWF are in very
good agreement across the offshore waters through Friday night.
The surface low currently about 60 nm south of Nantucket will
continue to track east northeast today, and then as the upper
level trough digging southeast through southern Quebec phases
with the associated upstream shortwave, the 00Z models all
indicate that low will rapidly intensify south of the Canadian
Maritimes tonight and Thursday. Models agree that this system
will have expansive gale force wind radii, and are consistent in
showing marginal gales skirting the outer northern NT1 and
possibly Georges Bank late tonight into Thursday evening. So
with about average forecast confidence, will retain the
previously forecast gales across ANZ900, ANZ905 and ANZ910
zones. By late Thursday and Thursday night, the high pressure
ridge should move off the coast, and drift east across the
waters Friday. Through Friday, will be using the 00Z ECMWF for
wind grids, but did use our in house adjustment to account for
their low bias in cold air advection today through Thursday
evening.

Late in the week and into the weekend, the 00Z models are
consistent in moving a vigorous upper level shortwave/possible
closed upper low to the mid Atlantic coast early Saturday and
east across the NT2 waters later Saturday into Saturday night.
The 00Z GFS and 00Z ECMWF have come into much better agreement
with the timing of the associated surface low, although the 00Z
GFS continued to be slightly south of the ECMWF. The 00Z UKMET
is a bit slower than the GFS/ECMWF consensus, but supports the
stronger ECMWF. The past couple runs of the GEFS also suggest
that the deterministic GFS may be too weak. Am favoring the
stronger ECMWF and as was done previously will use an even blend
of the 00Z and 12Z/28 runs of the ECMWF. Did then make some
adjustments to these blended winds to slightly expand areas of
gales, both ahead of the cold front Friday night, and associated
with the strengthening surface low Saturday and Saturday night.
Models are then in agreement that as the low accelerates
northeast toward Newfoundland, another high pressure ridge will
build east toward the mid Atlantic coast Sunday and Sunday
night.
.Seas...Both the 00Z Wavewatch III and 00Z ECMWF WAM are
reasonably well initialized with the west Atlantic wave heights
this morning. Used a 50/50 blend of the above guidance through
Friday, before switching to a 75% ECMWF WAM/25% WW3 blend Friday
night through the remainder of the forecast period, given our
preference for the ECMWF in the medium range.

.EXTRATROPICAL STORM SURGE GUIDANCE...N/A.

.WARNINGS...Preliminary.

.NT1 New England Waters...
.ANZ805...Georges Bank west of 68W...
     Gale Possible Saturday into Saturday night.
.ANZ900...Georges Bank east of 68W...
     Gale tonight.
     Gale Possible Saturday into Saturday night.
.ANZ810...South of New England...
     Gale Possible Saturday into Saturday night.
.ANZ815...South of Long Island...
     Gale Possible Saturday into Saturday night.

.NT2 Mid-Atlantic Waters...
.ANZ820...Hudson Canyon to Baltimore Canyon...
     Gale Possible Saturday.
.ANZ915...Hudson Canyon to the Great South Channel...
     Gale Possible Saturday into Saturday night.
.ANZ920...Baltimore Canyon to the Great South Channel...
     Gale Possible Friday night into Saturday night.
.ANZ905...The Great South Channel to the Hague Line...
     Gale tonight into Thursday night.
     Gale Possible Saturday into Saturday night.
.ANZ910...East of the Great South Channel and south of 39N...
     Gale tonight into Thursday.
     Gale Possible Saturday into Saturday night.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras
Canyon...
     Gale Possible Friday night into Saturday night.

$$

.Forecaster Clark. Ocean Prediction Center.



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