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000
AGPN40 KWNM 251459
MIMPAC

Marine Weather Discussion for N Pacific Ocean
NWS Ocean Prediction Center Washington DC
759 AM PDT Tue Jul 25 2017

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

12Z surface analysis shows the two main synoptic features to
affect the offshore and coastal waters over the forecast period
in a stable summer pattern; high pressure centered west of
California and an inverted or thermal trough over California.
This will produce strongest gradients and highest northerly winds
to 30 kt today and again late Fri into Sat off northern
California but otherwise winds to 20 kt common over the central
and northern PZ6 waters and far southeast PZ5 waters. The
northern waters will be affected by a high pressure ridge
extending from the high pressure through which a series of
weakening fronts will pass, with the first one now west of the
PZ5 waters trailing from low presure near 54N 141W, expected to
pass through the PZ5 waters tonight and early Wednesday, followed
by a second frontal system late Friday night into Saturday
night. Winds are not expected to exceed 20 kt with these fronts.

Another area of light winds will prevail in the southern PZ6
waters which will be dominated by a broad low pressure trough.

The 00Z models and the 06Z GFS/NAM along with the newer 12Z runs
of those two models are in good agreement with some differnces
developing mainly northwest of the waters by Saturday which will
have no significant effect on the offshore waters. Therefore the
00Z/06Z GFS look reasonable with latest grids based on the 00Z
GFS. For the morning update will maintain use of the present
grids with sime minor edits in deference to the 00Z ECMWF. No
warning headlines will be needed through the forecast period.

Seas...The 00Z ENP version of the Wavewatch III and the 00Z ECMWF
WAM appear well initialized compared to the 12Z regional sea
state analysis, and the two models agree within foot for much of
the period. No changes are expected at this time.

-----------------------------------------------------------------
PREVIOUS DISCUSSION...

No gale warning headlines in this issuance since gales
diminished over tonight as high pressure to the west continues to
drift farther west and inland low pressure trough weakens and
has resulted in a relaxed pressure gradient. However, gale force
winds still linger just east of the central waters. Geocolor
satellite images still show clearing skies over the PZ5 waters
but quite cloudy elsewhere. Maximum winds are just below gale
force range over the central waters and mostly from the north. 5
to 15 kt winds from the northwest are over the southern waters.
The NCEP map at 06Z has high pressure 1030 mb west of the region
that extends a ridge into the northern and southern waters.
Inland low pressure stretches southeast near the coast from low
pressure over northern California. Pressure gradient is
relatively tight over the central waters.

Models GFS/CMC/UKMETHR/ECMWFHR/NOGAPS/NAM have suited well with
the 06Z surface observations. The models only have high pressure
and inland trough as main synoptic features to agree on and they
show continued agreement in the short term. Will therefore retain
the winds from the previous forecast by using GFS in the short
term and then switch to ECMWFHR in the extended period.

.SEAS...they are relatively large over the central waters with a
10 ft peak. Otherwise seas range between 4 and 6 ft over the far
south and far north waters. NWW3 and ECMWFWAVE models have shown
good agreement with the 06Z observed seas pattern. Will use ENP
for seas. In the short term, seas will remain relatively high
over the central waters.

.EXTRATROPICAL STORM SURGE GUIDANCE...n/a.



.WARNINGS...Preliminary.

.PZ5 Washington/Oregon Waters...
     None.

.PZ6 California Waters...
     None.

$$

.Forecaster Bancroft/Musonda. Ocean Prediction Center.



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