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AGPN40 KWNM 231519

Marine Weather Discussion for N Pacific Ocean
NWS Ocean Prediction Center Washington DC
819 AM PDT Tue May 23 2017

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

Gale warnings in the short term over the central waters will be
retained then a high pressure ridge will dominate the forecast
region in the extended period. Geocolor satellite images show
anticyclonic circulation center west of the north California
waters. The latest observations show maximum winds over the
central waters. At 1200Z, the NCEP surface map has an inland
trough near the coasts from California to Washington states.
Weakening high pressure 1028 mb west of the region near 40N140W
is part of a broad high pressure with center 1039 Mb over the
central Pacific near 40N160W, that extends a ridge northeast into
the north waters and southeast into the southern waters. A cold
front is just over the northwest tip of the Washington waters.
Pressure gradient is tightening over the central waters.

Seas range between 4 and 6 ft over the southern waters while
they range between 6 and 8 ft over the central and northern
waters. NWW3 and ECMWFWAVE fit well the 12Z observed seas pattern
and both wave models have been quite consistent with the
observed seas pattern though NWW3 was a foot lower in areas with
higher winds. Will not make major changes to the previous
forecastand will continue with ECMWFWAVE guidance for seas.

The models CMC/GFS/UKMETHR/ECMWFHR have initialized well the 12Z
surface observations with just small differences on the position
of the weak high pressure west of the region. UKMETHR and GFS
suggest high pressure center while ECMWF and CMC have just a
ridge in the same area. These small differences do not project
differences in the synoptic pattern over the waters and so will
continue with GFS for winds. In the short term the models agree
on dissipating the high pressure west of the region.


00Z global models remain in good agreement through the forecast
period. Will lean towards the 10m boundary layer winds from the
00Z GFS initially for the wind grids as they match closely the
high resolution ASCAT-B scatterometer winds from the last 0445Z
and 0645Z passes. For later today and beyond as a cold front
drops SE over the waters, now analyzed just NW of the Washington
waters, will continue to use the representative 00Z GFS but with
a mix of 10m and first sigma level winds through use of a smart
tool which places the higher first sigma level winds over
unstable areas and 10m winds over stable areas. The GFS has good
support from the 00Z ECMWF/UKMET/global GEM.

Coastal trough near the California and Oregon coast will persist
into today as high pressure west of the region slowly weakens and
the aforementioned cold front moves over the region. Strong high
pressure is then expected to move into the eastern Pacific west
of the PZ5 waters later today and tonight while building a ridge
east into the PZ5 waters. Also a upper level vorticity max is
expected to dive southeast along the coast and should enhance
the coastal trough during this time period. This setup should
provide enough of a gradient to produce gales in the offshore
waters off Point Saint George beginning Tuesday night and
continuing through Wednesday night. Models in good agreement with
timing and location of gales during this time period. Again will
use a mix of 10m and 30m winds using the smart tool as the cold
front dropping through the area will provide some instability,
but as most of the upper level energy moves farther inland after
tonight most of the instability will be east of the area, and
then 10m winds will be used. Gradient begins to relax Thursday
and Thursday night as the upper level ridge and associated
surface high begin to weaken.

Farther north, a trough sets up along Vancouver Island Tuesday
night and persist into Wednesday night. GFS is showing a little
instability over the adjacent offshore waters during this time
period. GFS has 10m winds to gale force just north of the
offshore waters Tuesday night and again Wednesday then expanding
into the adjacent NE Washington zone Wednesday night. With some
instability possible over the region, continued to use the
stability tool with the 00Z GFS boundary later winds, but with
support from the 00Z GFS/UKMET 10m winds and 00Z GEM have above
average confidence in gales Wednesday night in that zone.
Gradient begins to relax Thursday.

Seas...The 00Z ENP NWW3 and 00Z ECMWF WAM are well initialized
compared to current observations and altimeter passes, so used
the representative 50/50 blend of the 00Z wave models for the
first period, then for tonight into early Thursday during the
period of gales used the higher 00Z ECMWF WAM before reverting
back to the 50/50 blend of the models after 18Z Thursday when the
model differences become small.



.PZ5 Washington/Oregon Waters...
.PZZ800...Inner Waters from Cape Flattery to Cape Shoalwater...
     Gale Wednesday night.
.PZZ815...Inner Waters from Florence OR to Point St. George...
     Gale Wednesday into Wednesday night.

.PZ6 California Waters...
.PZZ820...Inner Waters from Point St. George to Point Arena...
     Gale tonight into Wednesday night.
     Gale Possible Thursday.
.PZZ920...Outer Waters from Point St. George to Point Arena...
     Gale Wednesday into Wednesday night.


.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.