North Pacific Marine Weather Discussion

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AGPN40 KWNM 211546
MIMPAC

Marine Weather Discussion for N Pacific Ocean
NWS Ocean Prediction Center Washington DC
746 AM PST Tue Jan 21 2020

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

At 12Z as per NCEP surface analysis, a complex low pressure
system with a primary center at 986 mb near 49N 133W while a
second center has formed on the occlusion near 52N 136W 986 mb.
the occsion has moved inland over the Pacific NW while the
trailing and weakening cold front extends from Cape Mendocino
across the central PZ6 waters. The large system has been slowly 
weakening overnight as it approached and then lifted NW of the
Washington waters. As this occurrs, low end gales will impact the
PZ5 waters associated with the post-frontal cold advection s, 
low end gales will impact postions of the outer central and
northern PZ5 waters today, and gales should end toward evening as
the system continues to weaken several more millibars.

Then by tonight through Wed afternoon, conditions in strong 
south southwesterlies, across these previously affected waters, 
will remain subgale as the next weaker system approaches from the
SW. That being said, higher winds are possible closer to the
inner waters and especially near the coast on account of 
channeling of higher winds along the WA/OR coastal mountains.

All of the models from the previous forecast indicated the low
end magnitude occurrence with the previously forecasted gales.
This was still indicated as well, in the newly available 06z GFS
and also 06Z/12Z NAM. As such, no changes will be made on this 
evening update cycle for the winds through Fri night. The 12Z 
wave height analysis showed the highest seas over and just W of
the Oregon waters in line with mresent wave grids. No changes are
needed hear.

Beyond Fri night and while extending the grids to day 7, updated
the grods with an even blend of the current 06Z GFS with the 00Z
ECMWF and did the same for the associated wave models.
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PREVIOUS DISCUSSION...

At 0800Z, 984 mb gale center was located along a line from Buoy
46004 SSE to Buoy 46036. Both 00Z ECMWF and GFS initialize the
system near 985 mb at 0900Z and move it eastwards parallel to
British Columbia by this afternoon, then becoming a weakened 
negatively tilted surface trough axis right along the BC/WA/OR 
coast by 00Z Wed. Nevertheless, low end gales will still impact 
the PZ5 Outer waters until late this afternoon (00Z). Then as 
this trough pulls away tomorrow night, the next impulse upstream 
in the E Pacific will approach from the west. On Wed, The 
associated approaching warm frontal boundary ahead of this next 
system will only be accompanied by subgale south southwesterlies,
across the Outer and Inner PZ5 waters, as the only area of gales
would occur in the immediate Pacific Coastal nearshore waters 
adjoining the WA/OR coasts. This would be the result of the 
channel gaps between the coastal mountain ranges. Thereafter, 
another impulse from the SW will result in another surge of 25 to
30 knotters again late Wed night and Thu morning followed by a 
brief period of transient shortwave ridging will occur late Wed 
night thru Fri night. 

Across PZ6, near 1025 mb ridging will slide eastward today from
out at 145W along 30N, becoming centered over the Central and
Southern Outer and Inner waters by Wed afternoon, then remain in
place over the waters through Fri night. Winds will remain well 
below warning criteria, so much improved seas will result. Given
consistency with both NCEP models, will follow a 50/50 blend of 
the GFS and ECMWF thru about 0600Z Sat. Any low end gales should
end by 00Z Wed. Confidence in the model solutions in above 
average in the short and middle term. 

.Extended...The next significant cyclone, a near 980 mb surface
low will approach the PZ5 waters during Fri night, then pass NW
of the waters in a similar fashion to the present gales now impacting
this region. At this time, the 00Z NCEP models indicate only low
end gales for late Fri night into Sat with these gales ending by
00Z Sun. Another system approaches yet again Sun night but then 
moves across the Northern PZ5 waters, although the GFS is the 
only model that indicates gales with this one. Subgale 
conditions are indicated Monday and Monday night, but then the 
GFS indicates another larger area of gales on Day 7. Given that
only a low end gale is indicated in both of the NCEP models for
Fri into Sat, and the length of time out in the forecast, 
prudence dictates to keep the winds around 30 knots until there 
is more consistency with this. So will utilize the official 
forecast we are carrying already in the grids. From 18Z Mon to 
12Z Tue utilized a 50/50 blend of the GFS/ECMWF once more.
Weaker ridging is progged to remain in place across the PZ6 
waters through all of this time, with no warnings indicated. 

.Seas...The seas are initializing much better this week. Kept 
the 50/50 blend of the ENP/WAM through 06Z Fri. Thereafter, left 
in the inherited grids.

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

.WARNINGS...Preliminary.

.PZ5 Washington/Oregon Waters...
.PZZ905...Outer Waters from Cape Shoalwater to Cape Lookout...
     Gale today.

.PZ6 California Waters...
     None.

$$

.Forecaster Bancroft/Futterman. Ocean Prediction Center.