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AGPN40 KWNM 200339

Marine Weather Discussion for N Pacific Ocean
NWS Ocean Prediction Center Washington DC
839 PM PDT Mon Mar 19 2018

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

Low pressure will move northeast from an area west of the the
southern waters and pass through the central and northern waters
and that will result in elevated winds over the region. NCEP map
at 00Z has low pressure 992 MB near 33N143W with storm force
winds and an associated occluded front stretches east then
continues southeast as a warm front passing over the western
edge of the central and southern waters. Weak high pressure 1018
MB is centered over the far southern waters. Pressure gradient is
well relaxed over the region but is slowly tightening in the
vicinity of the front.

Seas are now largest over the western edge of the central waters
which is in line with the approaching low. Seas currently peak
at 9 ft over the outer central waters but will build and spread
to the north in the short term. In the extended period, seas will
also build form the northwest as another low pressure system
approaches from the northwest. NWW3 and ECMWFWAVE have very
similar solution to the forecast seas and so will just stay with

Global models GFS/ECMWFHR/UKMETHR/CMC/NOGAPS have generally
initialized the 00Z surface observations fairly well but marked
differences are in the wind speed around low to the west of the
southern waters. GFS/CMC/NOGAPS have initialized with storm force
winds which fits the observations while ECMWFHR and UKMETHR have
weaker winds. In the short term, the models agree on moving low
pressure northeast into the region and elevating winds over the
region to gale force. However, UKMETHR has no gale s in the
waters and the ECMWFHR takes the low pressure farther south as it
weakens it keeping wind below gale force. Since GFS has
initialized better than ECMWFHR and also brings the low to the
central waters with elevated winds, will stay with GFS.


18Z NCEP surface analysis shows a weak high pressure ridge over
the northern PZ5 waters and another weak area of high pressure
over the southern PZ6 waters. Latest observations and 18-19Z
ASCAT passes show a complex area of low pressure with storm force
winds to the north of the center, with NCEP analyzing the main
center near 36N 141W with a 990- mb center. The strongest winds
in the offshore waters are in the outer PZ6 waters in advance of
the approching occluded front and cold front. In the PZ5 waters
the highest winds are in the outer central waters in the NE flow
to the south of the ridge. These winds appear close to a blend of
the 12Z GFS 10m and first sigma level winds.

The 12Z models are in good agreement through Thu and then develop
some differences Thu night that become large by Sat. The cutoff
low west of Caifornia and the associated complex surface low will
move little over the next two days with multiple centers rotating
around one another. The frontal system approaching the waters
will move NE over the central and northern PZ6 waters later
tonight into Tue night while weakening, a trend indicated by
winds at buoy 46059 which have not been increasing and based on
GFS 10m/30m wind blend used, have near term gale warnings ahead
of this front only in central California zone PZZ830 late Tue
into Tue night but otherwise warning level winds W of the waters.
This complex system begins to open up aloft Tue night with the approach
of an upper low dropping S toward the PZ5 waters with the
southern low(s) ejecting NE and perhaps merging with a cold front
dropping through PZ5 waters Wed night and especially Thu, with
the cold front then passing through the central PZ6 waters Thu
and then the southern PZ6 area Thu night. For the wind grids used
the 12Z GFS 10m/30m blend with the 30m winds in unstable areas.
Models then diverge Thu night and especially Fri into Sat night
with respect to the strength and track of the surface reflection
of the upper low dropping SE through the PZ5 waters. After 03Z
Fri and through Sat blended the 12Z GFS 10m/30m winds with the
stronger 12Z UKMET resulting in areas of marginal westerly gales
over portions of the outer central and northern PZ6 waters Wed
night into Fri. Confidence at this time is low to moderate.

For Sat night preference shifts to 12Z ECMWF which is supported
by latest GEFS and ECMWF ensemble means and WPC medium range

.SEAS...A 3:1 blend of the 12z ECMWF WAM and 12Z ENP WW3,
respectively, is preferred initially and through tonight, before
shifting to the representative 12Z ENP WW3 Tue through Thu before
transitioning to a 50/50 blend of the 12Z models Thu night and
then 12Z ECMWF Sat night.



.PZ5 Washington/Oregon Waters...

.PZ6 California Waters...
.PZZ920...Outer Waters from Point St. George to Point Arena...
     Gale Possible Wednesday night.
     Gale Possible Friday.
.PZZ830...Inner Waters from Pigeon Point to Point Piedras Blancas...
     Gale Tuesday night.
.PZZ930...Outer Waters from Pigeon Point to Point Piedras Blancas...
     Gale Possible Thursday.
.PZZ935...Outer Waters from Point Piedras Blancas to Santa Cruz Island, CA...
     Gale Possible Thursday.


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