Marine Interpretation Message
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354
AGPN40 KWNM 200834
MIMPAC

Marine Weather Discussion for N Pacific Ocean
NWS Ocean Prediction Center Washington DC
134 AM PDT Sun Aug 20 2017

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

Based on the latest ASCAT pass and observations we will expand
gales into the far southeastern part of the southern Oregon
offshore waters for the early morning package, with gales
continuing over the eastern part of the inner northern California
offshore waters today into tonight. Otherwise, little change is
expected for the early morning forecast package from the previous
few OPC forecasts. The strong pressure gradient between coastal
and inland low pressure and high pressure centered west of the
northern California offshore waters will persist today into
tonight, and then slowly weaken later tonight through early
Tuesday as the high shifts southwestward and a cold front
approaches the Washington and Oregon waters from the west. The
front is expected to cross these waters Tuesday evening into
early Wednesday, with the front reaching northern California
waters Wednesday, and dissipating over central California waters
Wednesday night or early Thursday. The pressure gradient will
likely strengthen once again Thursday and Thursday night as high
pressure re-builds west of the region and the coastal trof
intensifies. We will keep winds below gale force over the
offshore waters later in the forecast for now, and continue to
evaluate the potential for gales especially over eastern portions
of the northern California offshore waters during the next few
days.

Tropical Storm Kenneth is forecast to become a hurricane
shortly, and track well to the south and then southwest of the
offshore waters over the next few days, with no major impact
expected on conditions over the offshore waters. For more
information on Kenneth please refer to the latest advisory from
the National Hurricane Center.

For the early morning package we will use the 00Z GFS 10 meter
winds, as has been the case over the past few forecast cycles,
and manually expand the winds somewhat over southeastern Oregon
waters to fit with the latest ASCAT pass.

.SEAS...As the 00Z ECMWF WAM indicates sea heights a little
closer to the latest observations and altimeter data over the
region we will begin the forecast with the 00Z WAM model output,
and then transition to a 50/50 blend of the WAM and Wavewatch
III model output by tonight, through the rest of the forecast
package. Per the latest observations sea heights range from near
17 feet or so in the gale warning area, to 4 to 5 feet or so
over the Washington offshore waters, and the southern part of
the southern California offshore waters. For the early morning
package we will also tweak wave height grids slightly near the
adjacent coastal waters, and TAFB waters to show a better
transition between forecast areas.

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

.WARNINGS...Preliminary.

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

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

$$

.Forecaster Mills. Ocean Prediction Center.



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