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AGPN40 KWNM 172034

Marine Weather Discussion for N Pacific Ocean
NWS Ocean Prediction Center Washington DC
134 PM PDT Sat Mar 17 2018

.FORECAST DISCUSSION...Major features/winds/seas/significant
.weather for the North Pacific N of 30N and E of 150W.

Weak low pressure remains positioned over Vancouver Island this
afternoon with a surface trough extending southward along the
Pacific Northwest coast. A surface ridge extends northward from
1023 mb high pressure analyzed west of the waters. Elsewhere, a
weakening cold front extends across the far southern California
waters. A recent ASCAT pass across the central and southern PZ6
waters supports 10-15 kt north to northwest flow over the area.

Conditions will remain relatively quiet over our offshore waters
through the weekend into early next week before a complex low
and its associated frontal system bring deteriorating conditions
by midweek. The 12Z models agree that a surface ridge will cross
the PZ6 waters tonight through Sun night, bringing light and
variable winds as the ridge axis passes over the region.
Meanwhile, deepening low pressure will become occluded well west
of the offshore zones and push a frontal system towards the PZ6
waters Mon through Tue. The 12Z GFS is the only model that depicts
marginal gales over the outer PZ6 zones ahead of this front Mon
night, while the 12Z ECMWF/UKMET/NAM all keep winds at 20-30 kt.
Therefore, will transition our official grids to the 12Z ECMWF
beginning 00Z Tue. Even applying a boost to the ECMWF grids still
keeps winds below gale criteria once the front reaches our

Unfortunately, the 12Z guidance offered little clarity in the
medium range. As the complex low west of the area approaches the
waters by Wed, the 12Z GFS tracks the low across the region about
12 hours faster than the rest of the global guidance. Meanwhile,
the 12Z ECMWF brings the low much further south than its previous
run, while the 12Z UKMET is most similar to the solution shown
by the 00Z ECMWF. Clearly, forecast confidence for the middle of
next week is quite low at this time. Have opted to use the 00Z
ECMWF wind grids from Wed night through Thu night until some
model consensus is reached. These grids are supported by the
12Z UKMET, but produce stronger winds behind the cold front that
crosses the region Wed through Thu night as low pressure drops
southeast from the Gulf of Alaska and nears the northern PZ5
waters Thu night.

While gales appear virtually certain west of the offshore zones
as the low deepens early next week, the 12Z guidance overall was
not as bullish with the wind speeds over our forecast waters by
midweek. Therefore, will cap the 00Z ECMWF winds at 30 kt on day
5 and not carry any warning headlines with this forecast package.

.SEAS...The 12Z Wavewatch/ECMWF WAM guidance initialized well
based on the latest sea state analysis. In fact, differences
between the wave models were fairly minor until the wind
solutions diverged late in the period. Favored a blend of the
12Z Wavewatch/WAM seas for the official wave grids through Wed.
Then, transitioned to the 00Z WAM Wed night through Thu night to
match up the highest seas with our wind grids.



.PZ5 Washington/Oregon Waters...

.PZ6 California Waters...


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