Marine Interpretation Message
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889
AGPN40 KWNM 230949
MIMPAC

Marine Weather Discussion for N Pacific Ocean
NWS Ocean Prediction Center Washington DC
249 AM PDT Mon Apr 23 2018

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

The 06Z surface analysis indicated a high pressure ridge
extending south-southwest from southern British Columbia through
the Washington and Oregon offshore waters, and then continuing
southwest to the west of the central and southern PZ6 waters. The
ridge has been slowly weakening. An inverted trough extended
from inland central and southern California NW and N along the
northern California coast and along the Oregon coast, where it
forms more of a weak lee trough. Still no ASCAT data, which is
coming in intermittently but coming in 10 hours late, and
therefore not of use. However the latest available reports mostly
from buoys are close to the model forecast fields and show winds
trending down as the gradient offshore weakens.

The 00Z models continue to be in very good agreement during the
short term period from today through early Wednesday morning.
The high pressure ridge currently over the northern waters will
continue to slowly weaken over the next 24 to 36 hours as a cold
front currently west of the area along 138-140W moves slowly
east. Also, the trough along the coast from northern California
to Oregon will gradually expand north to the Washington coast
today into Tue. Will populate the wind grids using the
representative 00Z GFS 10 meter winds through 12Z Wed as there
are few differences noted among the models in this timeframe.
Then looking ahead to Wed and beyond, there continue to be
differences with a cutoff low pressure area which is forecast to
develop just west of the northern California waters later Wed
before slowly moving east and re-forming a new weak center to the
north through the end of the week. The GFS appears to be an
outlier as it indicates the low further north and east closer to
the Oregon waters into Thu compared to the ECMWF/UKMET/CMC. Will
defer to the model consensus here and will use the current 00Z
ECMWF Wed and Wed night and then for Thu and beyond stay with the
previous grids based on the old 22/12Z ECMWF as it converges back
toward the 00Z GFS and Canadian on Fri while newer ECMWF turns a
portion of the low southeast into the PZ6 waters and will be in
line with WPC medium range guidance. The 00Z UKMET lifts the
upper and surface low out too quickly leaving more of a ridge off
California later Fri and is an outlier.

.SEAS...The 06Z sea state analysis indicated that observed seas
continue to be within a foot of the ENP/ECMWF WAM forecast
values. Similar to the wind grids, will populate the wave grids
using the 00Z ENP values through 12Z Wednesday, then transition
to ECMWF WAM.

.EXTRATROPICAL STORM SURGE GUIDANCE...N/A.


.WARNINGS...Preliminary.

.PZ5 Washington/Oregon Waters...
     None.

.PZ6 California Waters...
     None.

$$

.Forecaster Bancroft. Ocean Prediction Center.



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