Marine Interpretation Message
Issued by NWS
AGPN40 KWNM 292140
Marine Weather Discussion for N Pacific Ocean
NWS Ocean Prediction Center Washington DC
240 PM PDT Sat Apr 29 2017
.FORECAST DISCUSSION...Major features/winds/seas/significant
.weather for the North Pacific N of 30N and E of 150W.
Gale warnings in the far north zones have diminished over the
forecast waters and winds over the region will remain below gale
force threshold through the rest of the forecast period as high
pressure will dominate. The satellite images still show
anticyclonic air flow over most of the region except the far
north waters where clouds with cold tops are still moving east.
The latest observations including scatterometer pass at 1746Z
show higher winds over the north waters in just below gale force
threshold from the south and southwest. Winds are mainly 15 to 25
kt and they are form the north and northwest over most of the
region. The NCEP map at 1800Z has low pressure 993 MB now about
300 NM north-northwest of the region with its warm front
stretching southeast into the eastern portion of the washington
waters while its associated cold front is now entering the
washington waters. A trough still stretches along the coast of
California into the southern parts of Oregon coast. High pressure
now strengthened by 2 MB to 1031 MB in the last 6 hours is still
centered west of the southern waters near 36N134W. The pressure
gradient is just tight over the north portion of washington
waters and quite relaxed over the rest of the region. Elsewhere,
low pressure 1010 MB in the gulf of Alaska is part of the low
pressure described above. Farther west is still a broad area that
is dominated by low pressure with several centers. One low
pressure that still demands close monitoring is now 1006 MB east
of Japan near 33N156E as this low is still slated to end up in
the gulf of AK and force winds to be elevated to storm force
threshold and will also bring large period west swells to the
In the upper levels, the models GFS/CMC/ECMWFHR/UKMETHR suggest
energy embedded in an upper level trough stretching southeast
from the Gulf of AK that is moving over the for north waters. An
upper level cut off high pressure has a ridge with little to no
energy just west of the region. Meanwhile, there is a cut off
upper level low with significant energy centered just north of
Hawaii. Another area of significant energy is a cut off low just
west of the Aleutian Islands which extends a trough that has
energy that is maintaining low pressure east of Japan mentioned
above. In the short term, the models agree on pushing the energy
over the north waters to the northeast while building and
maintaining high pressure to the west of the region. The energy
over north Hawaii will drift south while most of the energy
associated with low to the west of the Aleutian Islands will
consolidate and move toward the Gulf of Alaska.
The models GFS/CMC/ECMWFHR/UKMETHR/NOGAPS/NAM have still
initialized well the 18Z surface observations with still just
minor differences within 1 MB on the central pressure values of
the low pressure to the northwest and high pressure west of the
region. As for the wind speed, ECMWFHR is still quite weak by 10
kt over GFS and UKMETHR is equally weaker than GFS with winds to
only 25 KT. CMC and GFS are evenly matched on winds over the
north waters and match the 30 kt winds over the north. So, will
stay with GFS for this forecast. In the short term, low pressure
will move north of the region and will pull a warm front
northeast of the north waters as a cold front moves east. High
pressure will continue to build west of the region and will
maintain a relaxed pressure gradient especially over the central
and southern waters through most of the forecast period.
.SEAS...The seas now have peaks to 12 ft over the southern
waters. The seas range between 6 and 11 ft over the southern
waters mainly due to large period swell and they range only
between 6 and 9 ft over the northern half of the waters. The wave
models NWW3 and ECMFWAVE still fit very well the observed 18Z
seas pattern and they have been quite consistent in the previous
runs. Will continue with NWW3 for the seas. Seas will continue to
subside over the southern waters to below 8 ft through the
forecast period but will build to 10 ft over the central waters.
briefly before subsiding to 8 ft in the extended period. The Seas
will start to build over the northwest waters in the extended
period mainly due to the large period swell from the west.
.EXTRATROPICAL STORM SURGE GUIDANCE...n/a.
.PZ5 Washington/Oregon Waters...
.PZ6 California Waters...
.Forecaster Musonda. Ocean Prediction Center.