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611
AGNT40 KWNM 161213
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
713 AM EST MON JAN 16 2017

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

As a high pressure ridge drifts SE across the NT1 waters light
winds (generally 10-20 kt or less) prevail throughout all of the
coastal/offshore waters at the moment. Highest seas throughout the
waters are only in the 4-6 ft range which are being handled
reasonably well by both the 06Z Wavewatch III and 00Z ECMWF WAM
models.

The latest models have now converged towards similar solutions
for the most significant weather feature expected over the next
several days. That is the models agree that after the high
pressure ridge with light conditions continues to drift SE across
the NT2 waters today/tonight that a warm front will develop off
the mid Atlantic coast Tue and lift NE Tue night with
strengthening associated gradients. Then early Wed the models all
forecast a developing triple point surface low to form S of Cape
Cod, track SE across the Srn NT1 and NE most NT2 waters later
Wed/Wed night, then move off to the E Thu. Due to the 00Z model
disparity, the previous forecast package continued to use the
official wind/wave grids, which were based on yesterday`s less
progressive 12Z GFS and 12Z Wavewatch III solutions, for Wed
through Fri night. But now, with the 06Z GFS and 00Z ECMWF
solutions becoming more similar (and being supported by their
respective 06Z GEFS and 00Z ECENS ensemble means), will now go
ahead and repopulate our forecast wind grids with a 50/50 blend of
the 06Z GFS first sigma level and 00Z ECMWF boundary layer winds
for Wed through Fri night. Will then also go ahead and repopulate
our forecast wave grids for these same times with a 50/50 blend of
the 06Z Wavewatch III and 00Z ECMWF WAM models. So as a result
will be making some major forecast changes, especially to the
previously forecasted gale warnings, in the next offshore
forecast package.





-----------------------------------------------------------------
PREVIOUS DISCUSSION...

Over the short term, the 00Z models remain in very good agreement
over the region. As a result, we will continue to rely on the 00Z
GFS for today through Tuesday night over the offshore waters.
High pressure will continue to build east and southeast over the
region today, and the begin to weaken and slide off to the east
and southeast of the waters tonight into Tuesday. An evening
ASCAT pass indicated maximum winds around 20 KT occurring over
eastern NT2 and northeast NT2 offshore waters which matches up
well with the 10 meter 00Z GFS winds. A cold front is still
forecast to drop south over NT1 waters tonight into Tuesday
before stalling along 40N or so by later Tuesday. The front will
return north as a warm front Tuesday night as low pressure forms
along the front near or east of Long Island by early Wednesday.
Overall, there will be no major changes over the short term part
of the forecast from the previous few OPC forecasts.

Over the long term, the 00Z global models are in rather poor
agreement. The 00Z GFS now appears to be too fast in moving the
low near Long Island eastward during Wednesday, as the remaining
non-GFS solutions are slower, or more similar to the 12Z GFS from
yesterday. For now, we feel the best course of action will be to
rely on the previous grids and forecast from around 12Z Wednesday
through the end of the forecast. This will maintain continuity
regarding all headlines over the offshore waters during the middle
to later portions of the week. Confidence in the longer term part
of the forecast is below average.

.Seas...Both the 00Z Wavewatch III and 00Z ECMWF WAM have intialized
the current seas heights quite well over the region. We will use a
50-50 blend of these two models into Tuesday night, and then to
match the wind forecast rely on the previous grids for Wednesday
through Friday night over the region. We will, however, make a few
manual edits to hopefully better match nearby coastal waters and
TAFB forecasts, and fit the wave heights forecast to the winds a
little better throughout the forecast. Overall, there will be no
major changes from the past few OPC forecast for the early
morning package.

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


.WARNINGS...Preliminary.

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

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

$$

.Forecaster Vukits/Mills. Ocean Prediction Center.



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