North Pacific Marine Weather Discussion

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AGPN40 KWNM 150342
MIMPAC

Marine Weather Discussion for N Pacific Ocean
NWS Ocean Prediction Center Washington DC
842 PM PDT Tue Aug 14 2018

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

The OPC-NCEP 00Z surface analysis shows a synoptic pattern that
has changed little over the last 24 hours, with a high centered
near 43N 147W with a ridge extending NE to just NW of Vancouver
Island. The only change is the high pressure and ridge arte about
6 mb weaker than 24 hours ago and latest surface observations and
earlier ASCAT data reflect that, with winds only 20 kt or less
except in the NW PZ5 waters where winds are 20 to 25 kt. There
was even a ship at 00Z reporting N 30 kt just N of the waters.
The gradient is tightest there, between a trough near the SW
coast of Vancouver Island and the ridge to the W. A weak trough
remained inland over California and extending NW toward the NW
California coast and a weak extension northward to the 
Washington coast. Will not make any changes to the ongoing 
forecast in this intermediate update given the agreement of the 
18Z GFS with the prior 12Z model package. Once again gales are
possible late on Fri or Fri night and into Sat night but they
will be confined to coastal areas around the Point St. George
area.

Please see the previous discussion for additional information. 
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PREVIOUS DISCUSSION...

Per the 18Z NCEP surface analysis a high pressure ridge was over
the offshore PZ5 and PZ6 waters while a low pressure trough was 
just inland, not far from the coast, extending from central 
California, northward to the Washington coast. The latest ASCAT
high resolution data revealed 15-25 kt winds over the northern
PZ5 waters with 10-20 kt winds over the southern PZ5 waters.
10-15 kt winds were noted over the central and southern PZ6
waters.

The latest 12Z guidance was in good agreement through roughly
Sunday 12Z with some differences on day 5. Those differences were 
upstream in regards to the evolution of a low pressure system 
over the Gulf of Alaska, which does have a slight impact on the 
how strong guidance models high pressure ridging expected to be 
over the offshore waters. Hence favored the 12Z GFS winds 
through Sunday 12Z, allowing the prior grids to remain in for the
rest of the forecast period. High pressure west of the waters
will extend its ridge over the PZ5 and PZ6 waters over the
period. Meanwhile a low pressure trough, currently near the 
California coast extending north to near the Washington coast,
will also persist over the period but strengthen late Friday into
Saturday and roughly maintain its same level of intensity through
the end of the period. Still anticipate increased winds over the
PZ5 and northern PZ6 waters later Friday through Sunday night 
but continue to believe any gales will remained confined east of 
the northern PZ6 waters, across the WFO coastal waters. None the 
less we will continue to monitor the situation over the forecast 
period in case trends begin to change.

.SEAS...Favored the 12Z NWW3 through Sunday 12Z, allowing the
prior grids to stay in place afterwards.

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

.WARNINGS...Preliminary.

.PZ5 Washington/Oregon Waters...
     None.

.PZ6 California Waters...
     None.

$$

.Forecaster Bancroft/Holley. Ocean Prediction Center.