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North Pacific Marine Weather Discussion

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AGPN40 KWNM 232145
MIMPAC

Marine Weather Discussion for N Pacific Ocean
NWS Ocean Prediction Center Washington DC
245 PM PDT Wed Sep 23 2020

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

The 18z surface analysis shows a cold front extending across the
Washington, Oregon and northern California waters from a triple 
point near the northern border of the inner WA waters 48N126W 
south-southwest to the outer northern CA waters 40N130W then to 
beyond 31N150W. A secondary surface trough also extends from the
main low pressure area centered across the Gulf of Alaska from 
near 51N138W southeast to near 43N131W. Recent ASCAT passes
missed likely gale force winds east of the front pinching along 
the OR and WA coast, however it did show gale force winds to the
W of the OR waters in the vicinity of 44N135W. To the southeast 
of the cold front high pressure continues to gradually erode 
across the central and southern California waters anchored by a 
1023 mb high centered near 32N133W.

As the aforementioned cold front pushes inland across the
northern coasts tonight, weakening dissipating southern portions
of the front will move across the northern and central CA waters
through tonight into early Thursday. Gale force conditions are 
expected to end tonight as well across the PZ5 waters. By 
Thursday, another area of low pressure will approach the WA/OR 
waters with guidance remaining consistent with gale force 
conditions materializing Thursday night into Friday as the low 
track across the WA waters and then inland across Vancouver
Island. Brief high pressure will prevail Friday and Friday night
before the associated stationary frontal boundary across the 
region will begin to lift N-NE as a warm front with the approach
of the next low pressure system. The associated cold front will 
impact the WA/OR waters late Saturday night into Sunday. At this 
time, guidance appears to suggest that gale force conditions will
remain N and W of the PZ5 waters.

Across the southern waters with regards to the high pressure, as
the cold front dissipates on Thursday, the high will begin to 
build eastward through Friday night. Meanwhile coastal troughing
is expected to develop across southern CA Friday night into
Saturday and stretch northward through Sunday night. The 
pressure gradient will strengthen along the CA coast and winds 
will increase 20 to 30 kt Thursday night and persist through 
Monday night. By late Sunday, a northern high pressure moving 
east will merge with the southern high and stretch the overall 
area of high pressure W of the CA waters to across the WA waters
and Vancouver Island.

Models remains in good agreement for the short term through
Saturday and Saturday night. With the pressure gradient to
increase winds off the CA coast this weekend and gradually shift
northward along the coast through Monday night, the 12z GFS
remains the outlier with regards to the only model with gale
force conditions off the SW Oregon and northern CA coast. A
viable solution at this point will be to maintain 25 to 30 kt
winds and continue to evaluate the next few model runs for a
upward trend if one develops the next day or two.

.SEAS...Seas across the northern waters range 10 to 15 ft with a
maximum of 17 ft noted off the coast of Washington. This is due 
largely to the cold front progressing eastward and inland
tonight. To the W of the cold front, higher seas were noted with
recent altimeter passes showing maximum seas to 24 ft in the 
vicinity of 44N140W. This area will generally translate E-NE 
with seas reaching 18 to 20 ft across the WA/OR waters tonight 
into early Thursday as seas continue to gradually and slowly 
subside.

.Extratropical storm surge guidance...N/A.


.WARNINGS...Preliminary.

.PZ5 Washington/Oregon Waters...
.PZZ800...Inner Waters from Cape Flattery to Cape Shoalwater...
     Gale Possible Friday.
.PZZ805...Inner Waters from Cape Shoalwater to Cape Lookout...
     Gale Possible Friday.
.PZZ905...Outer Waters from Cape Shoalwater to Cape Lookout...
     Gale Thursday night.
.PZZ810...Inner Waters from Cape Lookout to Florence OR...
     Gale today.
.PZZ910...Outer Waters from Cape Lookout to Florence OR...
     Gale Thursday night.
.PZZ815...Inner Waters from Florence OR to Point St. George...
     Gale today.

.PZ6 California Waters...
     None.

$$

.Forecaster Huffman. Ocean Prediction Center.