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AGNT40 KWNM 171928

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
328 PM EDT Tue Oct 17 2017

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

The latest NCEP surface analysis shows a cold front just SE of
the srn NT2 offshore waters this afternoon, and a high pres
ridge extending NE to SW along the New England through Mid Atlc
coast. The ridge is interacting with the frontal boundary, and
current wind observations off the SE coast indicate NE flow up
to 25 kt. However, the Ascat overpasses from 1530 UTC indicated
a large area up to 30 kt in the NE flow counter to the Gulf
Stream. The 12Z GFS indicates unstable lapse rates in the srn
offshore waters which is allowing stronger winds aloft to mix
down. The 12Z GFS also indicates that the front will move off to
the E tonight and Wed as the ridge continues to build over the
area. The previous forecast had gales to 18Z this afternoon, so
will allow the warning to expire as the 12Z models all indicate
the front will continue moving off to the SE and allowing the
pres gradient to weaken. The 12Z models all agree well on the
timing on the front and ridge, and also on the timing of another
weak cold front passing through NT1 Wed. As a result, planning on
starting out with the 12Z GFS 10m winds since they are
initialized well and are supported by the rest of the 12Z
guidance. However, will use first sigma winds in unstable areas
to reflect the deeper mixed layer expected in these regions.

In the medium range, the 12Z GFS/ECMWF agree fairly well on the
overall pattern, and indicate high pres will continue over the W
Atlc through the end of the forecast period. The models also
agree well on the timing of another cold front passing through
the NT1 waters Thu night into Fri. The 12Z GFS/ECMWF 10m winds
both indicate up to 25 kt in the SW flow ahead of the front over
the Gulf of Maine. This seems reasonable considering the cooler
SSTs in that region, so planning on staying with the 12Z GFS as a
result of the good model support. In addition, the models
indicate yet another cold front will approach from the NW on Sun,
though all 12Z solutions keep it to the W and NW of the offshore
waters by the end of the forecast period on Sun night. However,
the 12Z GFS is slightly stronger with the SW flow ahead of this
front on Sun night, and indicates a larger area with 25 kt than
the 12Z ECMWF. As a result, planning on continuing through the
remainder of the forecast period with the 12Z GFS, but will tone
done the winds slightly in deference to the weaker 12Z ECMWF

Seas...The 12Z Wavewatch and ECMWF WAM1 to 2 ft low off the SE
coast in the strong NE flow. However, the models are in good
agreement over the forecast period, so planning on using a 50/50
blend of the two solutions as a compromise to the minor
differences between them. Also, planning on adjusting seas higher
initially to account for the poor initialization off the SE

.Extratropical Storm Surge Guidance...The 12Z ESTOFS and ETSS
indicate a 1+ ft surge along the SE coast in the strong NE flow
offshore. The models both seem reasonable.


.NT1 New England Waters...

.NT2 Mid-Atlantic Waters...


.Forecaster Kells. Ocean Prediction Center. is the U.S. government's official web portal to all federal, state and local government web resources and services.