Marine Interpretation Message
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000
AGNT40 KWNM 240756
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
256 AM EST Sat Feb 24 2018

.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 indicates a weak low pres
system centered over the outer NT1 offshore waters, and a second
system moving into New England. Current surface observations
indicate winds up to 20 kt in the offshore waters as the winds
are light near the weak low in the nrn waters and also over the
srn waters where there is a high pres ridge. The Ascat overpass
from 0100 UTC last night indicated 25 kt in southerly flow in the
Gulf of Maine with a few 30 kt barbs in channeling flow between a
few islands along the coast of Maine. However, recent
observations indicate no more than no more than 20 kt along the
coast, including at a couple of elevated C-MAN stations just off
the coast of Maine. In addition, there are no observations in the
nrn outer NT2 waters in the cold advection behind the current
front over the area. The 00Z GFS winds are initialized slightly
high in the Gulf of Maine, but otherwise within 5 kt of the data
in the rest of the offshore waters. However, the 00Z models all
indicate the winds will increase today as the system currently
over New England moves offshore and passes through the area
today into tonight, with the highest winds over the outer NT2
offshore waters in the vicinity of the Gulf Stream. The 00Z GFS
seems representative with the timing of this system, and is
slightly stronger than the rest of the 00Z models with the winds.
As a result, planning on starting out with the 00Z GFS 10m
winds, except will use first sigma winds in unstable areas.

The 00Z models then indicate a developing low pres system will
move NE across the nrn offshore waters Sun into Sun night. The
00Z GFS/NAM/ECMWF/GEM all indicate 30 to 35 kt winds developing
ahead of the associated warm front across the Gulf of Maine,
while the 00Z UKMET is a little weaker with 25 kt. However, the
GFS and ECMWF 925 mb winds have been indicating a moderately
strong low level jet developing just ahead of the warm front,
with winds in the 45 to 50 kt range. This should induce some
vertical mixing, and the previous forecast indicated gales at the
surface for a brief period late Sun into Sun night. Confidence
remains about average, so planning on continuing previous
headlines in the next forecast package. In addition, will
continue with 00Z GFS through Tue. However, will boost winds 15
percent in cold advection to account for the low wind bias the
models have had this winter.

In the medium range, the GFS and ECMWF start to diverge, with the
GFS indicating another cold front moving through the NT1 waters
Wed and Wed night. The 00Z ECMWF is slower and weaker with the
system, and the 00Z UKMET/GEM generally supports the 00Z ECMWF.
As a result, have a slight preference for the 00Z ECMWF solution,
so planning on transitioning to it from 00Z Wed and continuing
with it through the remainder of the forecast period.

Seas...Both 00Z wave models are initialized within a ft or two of
current data in the offshore waters, though the 00Z Wavewatch is
low in cold advection E of the area near 40W. However, the models
agree fairly well in the short range in the offshore waters, so
planning on using a 50/50 blend of the two as a compromise to the
minor differences. Will then transition exclusively to the 00Z
ECMWF WAM from 00Z Wed onward to match the preferred timing and
winds of the 00Z ECMWF.

Extratropical Storm Surge Guidance: The 00Z GFS indicates strong
easterly flow off the mid Atlc coast Sun into Sun night, and the
00Z ESTOFS continues to indicate a surge of just over a foot from
the coast of central New Jersey through eastern Long Island. The
model also indicates surge values up to 2 ft in Long Island
Sound, with the highest to the W near New York by late Sun. The
00Z ETSS continues to run less than half of what is shown by the
ESTOFS, and seems underdone.

.WARNINGS...Preliminary.

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

.NT2 Mid-Atlantic Waters...
     None.

$$

.Forecaster Kells. Ocean Prediction Center.


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