000
AGPN40 KWNM 250936
MIMPAC

Marine Weather Discussion for N Pacific Ocean
NWS Ocean Prediction Center Washington DC
236 AM PDT Sun Oct 25 2020

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

The 06z surface analysis shows a surface trough axis extending
from the northern California coast near Cape Mendocino arcing
northwestward to just west of Vancouver Island near 50N129W.
Recent ASCAT passes indicated only a subtle wind shift across
the boundary which is expected to weaken through Sunday.
Otherwise, northerly surface winds prevail across much of the
offshore waters on the east and southeastern periphery of a 1033
mb high pressure centered well west of the Oregon waters near
44N141W. ASCAT passes between 03z and 06z showed a fairly large
area of 20 to 25 kt winds stretching from the Oregon waters
southward to the central California waters. Within this broad
area, specifically across the northern California waters, 25 to
30 kt N winds are noted as this is where the pressure gradient is
strongest between the high to the west and lower pressure across
interior California. Finally, a weak 1014 mb low is centered
across the southern CA waters near 32N123W with a surface trough
extending southwest to beyond 30N124W.

The high pressure to the W of the zones will slowly move
northward and then northeastward through Sunday night and
eventually prevail across the WA and northern OR waters through
Wednesday night. Meanwhile, troughing along the California coast
will strengthen and extend northward along the Oregon coast
though Sunday and persist through Monday before beginning to
weaken gradually thereafter. At this time, gale force conditions
are expected across the northern CA and southern OR zones for a
brief 6 to 12 hour window late Sunday into early Sunday night.
Thereafter, the pressure gradient between the troughing and high
pressure to the NW will begin to relax. While the high prevails
across the PZ5 waters late in the forecast period, it will begin
to erode Wednesday night into Thursday as the next cold front
approaches from the west. Southerly winds will increase on
Thursday across the far northern waters as the front reaches the
outer zones and then stalls while another low forms to the W-SW
of the Oregon waters and approaches the PZ5 waters Thursday night
into Friday.

The models are in fairly decent agreement in the short term with
respect to the brief window of gales off the northern California
coast and the movement of the high to the N and then NE. The
pressure gradient will remain strong across the northern CA and
southern Oregon waters until Monday night and then begin to relax
Tuesday and Tuesday night. Populated wind grids with the 00z GFS
through 00z Wednesday, and then transitioned to the 00z ECMWF as
it seems to handle the front that approaches the outer WA waters,
and the low that develops to the SW of the PZ5 waters Thursday
better than the GFS. The 00z UKMET and CMC also show support for
the low to develop and move northeastward toward the PZ5 waters.
With regards to strength, while it is beyond the 5 day forecast,
will continue to update the possibility of gales with the low. At
this time the ECMWF is the more robust solution, as the UKMET and
CMC are below gale, but will leave for now and update as it moves
closer to the 120h window.

.SEAS...The highest wave heights were noted off the coast of
northern California on the 06z sea-state analysis offshore of the
waters between Point Saint George and Cape Mendocino. Otherwise,
seas range generally 5 to 9 ft across the PZ5 waters, 6 to 12 ft
across the northern and central PZ6 waters, and 3 to 6 ft across
the southern PZ6 waters. With the brief period of gale force
conditions expected late Sunday, seas will build across the
northern CA waters 14 to 15 ft and then begin to subside through
Monday night. In keeping with the corresponding wind grids, the
00z WaveWatch ENP was utilized for the wave height grids through
00z Wednesday, and then a transition to the 00z ECMWF WAM was
used for the latter portion of the forecast.

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


.WARNINGS...Preliminary.

.PZ5 Washington/Oregon Waters...
.PZZ815...Inner Waters from Florence OR to Point St. George...
Gale today into tonight.

.PZ6 California Waters...
.PZZ820...Inner Waters from Point St. George to Point Arena...
Gale today into tonight.

$$

.Forecaster Huffman. Ocean Prediction Center.