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AGNT40 KWNM 180128

.Marine Weather Discussion for N Atlantic Ocean
.NWS Ocean Prediction Center Washington DC
830 PM EST SUN 17 DEC 2017

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

A north to south oriented high pressure ridge was centered
across the offshore waters at 00Z, while a weak stationary front
extended east across the waters off the Delmarva Peninsula. The
latest models again trended slightly stronger with the post-
frontal west to northwest winds across the eastern NT1 and
northeastern NT2 zones Tue night into Wed. As a result, we have
increasing forecast confidence that there will be a brief period
of gales across the Gulf of Maine/Georges Bank and the outer
ANZ905 waters at that time. The models then all forecast
developing low pressure or a series of lows will develop and
move east across the southern NT2 waters Wed night and Thu. The
past few runs of the ECMWF have trended south with the low
track(s). The guidance is also consistent that winds associated
with the low and front should increase to 30 kt or so over the
waters south of Cape Hatteras Wed night and Thu. Made a few
adjustments to the Tue night/Wed wind grids to incorporate some
of the higher 18Z GFS winds, but otherwise did not make any
significant changes to the previous OPC grids. The 18Z Wavewatch
III and 12Z ECMWF WAM are equally well initialized with the wave
heights across the west Atlantic this evening.

...Previous Discussion...

Current Conditions...The 12z ncep surface analysis shows a warm
front extending NW to SE across the northern nt2 waters from the
southern New Jersey coast. Otherwise, the analysis shows a high
pres ridge building SE into the nt1 area, with another ridge
moving E over the nt2 waters. Latest available ascat hi-res and
ascat passes from a few hours ago indicate 20 to 25 kt winds in
NW flow over the Georges Bank and NE nt2 waters, but elsewhere
taper the winds to 10 to 20 kt over the nt1 waters, and to 5 to
15 kt across the central and southern nt2 waters. The warm front
will drift NE over the northern nt2 waters tonight. A weak low
is expected to form along the front early Mon, then pass E over
the northern nt2 waters later Mon. A cold front will pass SE
across the offshore waters Tue night and Wed, then stall across
the southern nt2 waters late Wed and Wed night. Another low will
pass E over the southern nt2 waters Wed night and Thu, while
pulling an associated cold front SE over the area.

Models/Forecast...The 12z medium range models are in good
overall agreement across the offshore waters during the forecast
period, except there are timing and strength differences with
the low passing over the nt2 waters on Wed night and Thu. Will
use a 50/50 blend of the ecmwf/gfs 30m for wind grids for Tue
night and Wed, since it looks like the best comprimise solution.
Otherwise, the ecmwf looks representative enough to be used for
the wind grids. Am not planning to make any significant changes
to the current forecast trend.

Seas...Overall the 12z wna wavewatch and 12z ecmwf wam both
initialized well across the offshore waters, although the wna
wavewatch likely under initialized the wave heights over the SE
nt1 and NE nt2 waters by 2 to 3 feet. The wavewatch and ecwmf
wam are in decent overall agreement during the forecast period,
with only minor differences noted in the offshore waters. Since
the ecmwf is the preferred model for the wind grids over the
forecast period, a 75/25 blend of the ecwmf wam and wna
wavewatch will be used for the wave height grids in order to
maintain consistency.

Extratropical Storm Surge Guidance...N/A.


.NT1 New England Waters...
.ANZ800...Gulf of Maine...
     Gale Possible Tuesday night into Wednesday.
.ANZ805...Georges Bank west of 68W...
     Gale Possible Tuesday night.
.ANZ900...Georges Bank east of 68W...
     Gale Possible Tuesday night into Wednesday.

.NT2 Mid-Atlantic Waters...
.ANZ905...The Great South Channel to the Hague Line...
     Gale Possible Tuesday night into Wednesday.


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