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AGNT40 KWNM 240759
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
259 AM EST Wed Jan 24 2018

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

The red and purple hues in the latest GOES-16 RGB air mass
imagery - representing a drier and cooler air mass - indicate
the cold front has pushed E across most of the northern offshore
zones this morning, and lightning data suggests the convection
and thunderstorms coincident with strongest winds ahead of the
pre-frontal trough have moved east of the OPC forecast area.
Earlier ASCAT overpasses around 0215z returned widespread gales
across OPC waters, but not quite to storm force as was in the
grids. But based on the higher resolution guidance from the 00z
NAM and 04z HRRR - and to a lesser extent the 00z UKMET and GFS -
there still remains a likelihood that strongest winds in the low
level jet (65-75kt) did mix over the warmer waters of the Gulf
Stream in outer zones during the past several hours. By the time
of the next upcoming forecast package, these strongest winds -
and all hazard winds for that matter - will be just east of OPC
waters and will allow all headlines to expire accordingly.
Secondary cold front expected to pass across the northern waters
later today and tonight, with 00z models in good agreement
keeping winds to 30 kt and below hazard criteria in NW flow that
persists through late Fri. Worth mentioning light freezing spray
is expected across the northern waters from near Sandy Hook, NJ,
northward across the Gulf of Maine Wed night through Thu night.
For desired wind grids used an even blend between the 00z GFS
first sigma layer and 00z ECMWF winds through late Fri.

A cold front approaches the northern waters Sat, with winds up to
30 kt in the grids across the Gulf of Maine. Good agreement among
00z models regarding the timing of the slowly approaching front.
00z GFS does indicate a possibility of minimal gales Sat, but
with relatively stable flow over the cool SSTs, will opt for the
more conservative approach from the non-NCEP guidance. Stronger
cold front moves offshore Sun and Sun night, and along with it
the next best chance for gales. GFS remains too fast compared to
other global guidance, while the UKMET develops a sub-1000 hPa
low over the Gulf of Maine by 12z Mon. The 00z ECMWF remains an
excellent consensus solution, is well supported among ensemble
means, and has remained consistent versus its previous 12z
cycle. Given the uncertainty among the models, will opt to
continue to cap winds at 30 kt.

Seas: 00z WAM was performing better over the W Atlantic on the
06z sea state analysis, and intend to use its guidance throughout
the forecast period. Prefer its slightly higher values in
persistent NW flow through late Fri (2-3 ft higher than the WW3).
Seas up to 12 ft expected in the Gulf of Maine Sat, then greater
than 12 ft over the central waters late Sun ahead of strong cold
front.

Extratropical Storm Surge Guidance: no major deviation from the
latest surge guidance appears necessary over the next few days
across the area.


.WARNINGS...Preliminary.

.NT1 New England Waters...
     None.

.NT2 Mid-Atlantic Waters...
     None.

$$

.Forecaster Collins. Ocean Prediction Center.



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