000
AGPN40 KWNM 201525
MIMPAC

Marine Weather Discussion for N Pacific Ocean
NWS Ocean Prediction Center Washington DC
825 AM PDT Tue Apr 20 2021

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

High pressure will persist to the west of the north waters while
strong inland trough along California coast will start to weaken
slowly into the extended period. Latest NCEP surface weather map
has inland low pressure 1011 mb over north California with a
front extending north along the Oregon and Washington coast and a
trough extending south along the California coast. High pressure
1035 mb near 45N135W extends a ridge southeast into the central
and southern waters. Pressure gradient is tightening over the
central waters where winds are highest. The models have remained
fairly consistent since the last model run. No major changes from
previous forecast will be made on this issuance and will
continue to use the model choice as described in the previous
discussion below.


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PREVIOUS DISCUSSION...

The pattern ahead remains relatively quiet with high pressure
dominating the area, while a coastal trough along the southern
Oregon and California waters will strengthen for a few days
before weakening later in the period. The 06 UTC NCEP surface
analysis shows a 1036 mb high centered W of the southern PZ5
waters while a stationary front is hung up just E of the coastal
ranges of Washington and Oregon. Meanwhile, the southern portion
of the front continues to advance S-SW into central and southern
California. This front will stall and help to tighten the
pressure gradient along the coastal waters extending into the
inner southern PZ5 and most of the inner PZ6 waters as high
pressure elongates W of the outer waters. Gales will stay
confined to the nearshore waters, but winds will be 25-30 kt in
the aforementioned inner waters through tomorrow night with gusts
to low-end gale force. Another area of brisk 25-30 kt winds will
extend into the inner northern PZ5 waters at the same time. Both
areas of wind and associated seas of 14-16 ft will diminish
heading into Fri.

High pressure will stretch N-S W of the outer waters through Fri,
then one piece will move N into the Gulf of Alaska, while the
southern piece sets up just W of the outer southern PZ6 waters. A
cold front will approach and move through the PZ5 and northern
PZ6 waters Fri night into Sat, while low pressure traverses the
outer PZ5 waters into Sun. The GFS was used through early Mon,
then a blend of the GFS and ECMWF was used into early Tues to
account for a weaker low and associated front.

.Seas...Will use the GFS wave guidance through early Mon, then a
blend of the GFS wave and EC WAM through the early Tue period
with little adjustment anticipated.


.EXTRATROPICAL STORM SURGE GUIDANCE...N/A.


.WARNINGS...Preliminary.

.PZ5 Washington/Oregon Waters...
.PZZ800...Inner Waters from Cape Flattery to Cape Shoalwater...
Gale Wednesday night.

.PZ6 California Waters...
.PZZ820...Inner Waters from Point St. George to Point Arena...
Gale tonight.
.PZZ825...Inner Waters from Point Arena to Pigeon Point...
Gale tonight.

$$

.Forecaster Musonda/Folmer. Ocean Prediction Center.