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538
AGPN40 KWNM 251431
MIMPAC

Marine Weather Discussion for N Pacific Ocean
NWS Ocean Prediction Center Washington DC
731 AM PDT Fri May 25 2018

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

Only some small changes will be made to the forecast grids for
this morning`s update. Model agreement is good for the forecast
period, with some of the minor differences noted in previous runs
resolving. Prefer the use of the 10m GFS for the majority of the
forecast, with the NAMnest used near the coastal waters through
the early periods, as it seems to capture the observed winds a
bit better than the global models.

With good agreement in the wave models, will use a blend of the
ECMWF WAM and the WW3.

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PREVIOUS DISCUSSION...

Areas of increased wind activity will be the northwest portion
of the Washington waters and the eastern portion of the central
waters. The northern area will be impacted by a front that will
be associated with low pressure that will move into the Gulf of
Alaska while the central region will be a result of combining
effects of high pressure build up to the west and strengthening
of inland trough along the California coast. Latest GOES16 RGB
satellite images still show mostly warm and thin clouds across
the region. This is depicted well on the NCEP map at 06Z that has
high pressure 1032 MB due north of the Hawaiian Islands that
extends a ridge northeast into the northern waters. Weak Low
pressure 1016 MB about 300 NM west of the southern waters has a
weak front that extends northeast. Models agree well on weakening
and dissipating this low while strengthening high pressure that
will move east closer to the forecast waters.

At 500 MB, models depict energy embedded in almost cut-off low
west of the southern waters with an upper level ridge just
behind. In the short term, the energy will shift inland and a
ridge will lie across the waters. Persistent inland energy will
force deepening of the inland trough. spill off energy form
trough in the Gulf of Alaska will also touch the far north
Washington waters briefly. Otherwise, an upper level ridge will
persist across most of the region.

Global models GFS/CMC/UKMETHR/ECMWFHR have initialized fairly
well the 06Z surface observations over the forecast region. In
the short term the only differences are about the central
pressure value and actual position of high pressure to the west
of the southern waters as its proximity to the region will have a
direct effect on the pressure gradient over the central waters.
CMC keeps the center much closer to the waters and hence has
stronger winds to 40 kt over the central waters while GFS has
winds to 35 kt. ECMWFHR and UKMETHR depict weaker winds and so
will stay with GFS for winds to keep gales in the forecast.

.SEAS...They are still relatively small and they range between 6
and 9 ft across most of the central and northern region and are
just below 6 ft over the far southern waters. NWW3 and ECMWFWAVE
models fit well the observed seas pattern over the forecast
region and the high seas area. Both wave models agree well in the
short term on keep seas relatively small over the region. Will
stay with NWW3 for seas.

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


.WARNINGS...Preliminary.

.PZ5 Washington/Oregon Waters...
     None.

.PZ6 California Waters...
.PZZ820...Inner Waters from Point St. George to Point Arena...
     Gale Possible Tuesday night.
.PZZ825...Inner Waters from Point Arena to Pigeon Point...
     Gale Possible Tuesday night.

$$

.Forecaster Sommerville/Musonda. Ocean Prediction Center.



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