Marine Interpretation Message
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000
AGNT40 KWNM 072108
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
408 PM EST WED DEC 7 2016

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

A 1524Z high resolution ASCAT-A scatterometer pass supports the
decreasing trend of winds over the offshore waters...in particular
over the central and northern NT2 waters where there were gales in
an earlier ascat pass. In the data-free gap to the east between
passes a ship reported west 40 kt at 18Z just east of ANZ925 but
12Z GFS first sigma level winds and 12Z ECMWF 10m winds if boosted
support winds in the low 30s in that area. 12Z GFS first sigma
level winds appear representative and used near term through
tonight for diminishing winds as low pressure just east of the
waters moves off to the east...except some initial upeard
adjustments over the outer NT2 waters.

Then Thursday into Saturday night the 12Z models share similar
forecast timing for an arctic cold front to sweep southeast across
the waters Thursday into Thursday night with the coldest air so
far this season. The consensus of the 12Z models is to forecast a
slightly weaker west to northwest gradient late Friday and Friday
night when the strongest gradients are expected as a strong high
pressure ridge builds in from the west. With the associated 500mb
flow pattern similar in the models through this period will
continue to populate winds with the stronger 12Z GFS first sigma
layer winds through Saturday night. Made only minor edits over
the northern NT2 waters and far southern NT1 waters and maintain
areas of marginal gales with moderate confidence. Once again a
lack of digging of a shortwave trough as it moves offshore Friday
into Friday night results in gales not extending south of ANZ920.
Passage of this 500 mb shortwave appears followed by the strongest
winds. The 12Z global GEM versus its stronger previous run shows
less widespread area of gale force boundary layer winds...mainly
in outer waters while the 12Z UKMET/ECMWF mainly have areas of 30
kt 10m winds which when boosted may support marginal gales as in
GFS. with its stronger first sigma level winds for Friday through
Saturday night.

Then in the longer range...Sunday through Monday night...12Z
models differ in the timing of a warm front to develop offshore in
a strengthening southerly gradient. 12Z ECMWF appears slower than
other models with a greater spread inland with the associated low
pressure areas. Favor the 12Z GFS 10m winds during this period but
time shifted 6 hours slower...to a give a better match with 12Z
GEFS and 00Z ECMWF ensemble means. Have posted gale headlines for
Day 5 given some model support mainly over the NT2 waters and
capped the winds at 45 kt given the model differences.

.Seas...The 12Z Wavewatch III has initialized the seas across the
NT2 and southern NT1 waters too low. Will use the more
representative 12Z ECMWF WAM into Friday followed by a blend with
25 percent of 12Z MWW3 through Saturday night. After that time-
shifted the 12Z MWW3 6 hours slower for reason noted above.

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

.WARNINGS...Preliminary.

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

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

$$

.Forecaster Bancroft. Ocean Prediction Center.



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