AGPN40 KWNM 191409
MIMPAC

Marine Weather Discussion for N Pacific Ocean
NWS Ocean Prediction Center Washington DC
709 AM PDT Sat Sep 19 2020

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

The latest model guidance indicates that a high pressure ridge
west of the pz6 waters will continue to combine with a low
pressure trof along the California coast to produce northwest
winds up to 25 knots south of Point Conception today into
tonight. By Sunday night the strongest conditions of 25 knots
will then shift north to a position west of Point Reyes. Farther
north, a cold front will approach the pz5 waters by Tuesday, then
move across the offshore waters Tuesday night and Wednesday. Gale
force winds are still expected in the southerly flow ahead of the
front late Tuesday into Wednesday. For wind grids will continue
to use the current grids throughout the forecast period. Current
warnings look reasonable and few changes should be needed on the
next offshore waters forecast.

For wave height grids will also continue to use the current grids
throughout the forecast period.

Extratropical storm surge guidance...n/a.

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PREVIOUS DISCUSSION...

Per the preliminary 06z NCEP surface analysis a low is currently
to the N of the offshore zones. A high pressure center is well W
of the southern zones, and the associated ridge expands E into
the southern PZ5 and PZ6 waters. A weak trough is located along
the southern California coast. ASCT data from ~0500z show an
area of winds to 30 kt in the coastal S California waters
associated with a moderate pressure gradient between the high
center to the W and the coastal troughing. Otherwise ASCT data
from ~0545z show winds 15 kt or less in the PZ5 and N PZ6 waters.

Low pressure well N of the waters will move E, and a new low will
develop in the cold front W of the waters today. The new low and
associated cold front will weaken as they approach the offshore
zones, and enter the outer N California waters tomorrow night.
The low and front will dissipate in the inner waters by Mon
night. A strong low will move into the Gulf of Alaska, and the
associated front will enter the PZ5 waters Tue, and PZ6 waters
Tue night. Expect gale force conditions across most of the PZ5
waters as the front passes through Wed. The N PZ6 waters will
have winds to gale force as the front sweeps through Tue night
and Wed. Post-frontal winds to 25 kt will hang around in the PZ5
waters for the remainder of the forecast period. High pressure
well to the W extends into the S PZ5 waters and PZ6 waters at the
beginning of the forecast period. The weak low to form W of the
waters will erode the high pressure field S Sat night to Mon.
Following the low passage Mon high pressure will briefly extend
back NE into the PZ5 waters, then again be pushed S by the strong
frontal system that enters the waters Tue. However the high
pressure will be strong enough to keep most of the hazardous
conditions N of the central California waters. After the strong front
passes, the high pressure ridge axis will extend NE again into
the central PZ5 waters. A weak low pressure trough will persist
along the southern California coast for most of the forecast
period.

Global model guidance continues to be in good agreement in the
near-term and extended ranges. The biggest difference remains
with the low center placement in the Gulf of Alaska, but the
models are handling the front location and timing pretty
consistently with one another. However, the GFS begins to differ
from the ECMWF, CMC, and UKMET beyond day 5. For the wind grids
will populate with the GFS through Thu 03z, and use the ECMWF
beyond.


.SEAS...The seas are initialized fairly well with available obs
and altimeter data. It does appear both the NWW3 and ECMWF WAM
are over doing the seas in a few spots, but this only appears to
be by a couple feet or so. To remain consistent with the wind
grids, will populate with the same philosophy. For the seas will
populate with the NWW3 through Thu 03z, and the ECMWF WAM for the
remainder of the grids.


.EXTRATROPICAL STORM SURGE GUIDANCE...



.WARNINGS...Preliminary.

.PZ5 Washington/Oregon Waters...
.PZZ800...Inner Waters from Cape Flattery to Cape Shoalwater...
Gale Possible Tuesday night.
.PZZ900...Outer Waters from Cape Flattery to Cape Shoalwater...
Gale Possible Tuesday into Tuesday night.
.PZZ805...Inner Waters from Cape Shoalwater to Cape Lookout...
Gale Possible Tuesday night into Wednesday.
.PZZ905...Outer Waters from Cape Shoalwater to Cape Lookout...
Gale Possible Tuesday into Tuesday night.
.PZZ810...Inner Waters from Cape Lookout to Florence OR...
Gale Possible Tuesday night into Wednesday.
.PZZ910...Outer Waters from Cape Lookout to Florence OR...
Gale Possible Tuesday night.
.PZZ815...Inner Waters from Florence OR to Point St. George...
Gale Possible Wednesday.
.PZZ915...Outer Waters from Florence OR to Point St. George...
Gale Possible Tuesday night.

.PZ6 California Waters...
None.

$$

.Forecaster Nolt/Joseph. Ocean Prediction Center.