Marine Interpretation Message
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000
AGPN40 KWNM 181458
MIMPAC

Marine Weather Discussion for N Pacific Ocean
NWS Ocean Prediction Center Washington DC
758 AM PDT Fri Aug 18 2017

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

The 12Z OPC surface analysis depicts a cold front extending
across the northwest portion of the PZ5 waters. Meanwhile, the
enhanced gradient persists off the Oregon and northern California
coast between high pressure west of the waters and an inland trough
over California. An earlier ASCAT-B pass at 0446Z showed a swath
of 25 to 30 kt northerly winds over the coastal and inner offshore
zones west of Point Saint George. While gales are expected later
today over the coastal waters, will maintain wind speeds just
below warning criteria in our waters through tonight.

Confidence remains high for gales this weekend over the inner
waters from Point Saint George to Point Arena. The 00/06Z GFS
and NAM as well as the 00Z ECMWF/UKMET have consistently showed
gales expanding into this zone for several days now as high
pressure builds eastward and further strengthens the gradient.
The gale warning for PZZ820 now begins 21Z Saturday and runs
through 03Z Monday. The inherited warnings for PZZ815/825 will be
dropped as the latest guidance still indicates sustained winds
will remain below warning criteria, although some gale force
gusts can be expected.

Overall, the GFS remains the preferred solution based on its
run to run continuity with support from the rest of the global
guidance. Have transitioned to the 00Z ECMWF winds after 00Z
Wednesday to depict a slower progression of the approaching cold
front, which is supported by the GEFS/ECMWF ensemble means. This
also matches up well along our interface with the coastal WFOs.


.SEAS...A 1132Z Jason-3 altimeter pass off the northern California
coast showed seas to 12 ft roughly 50 nm west of Cape Mendocino.
The ECMWF WAM matched up better with obs for the 12Z sea state
analysis, so this model was used through tonight with a slight
boost applied based on the low bias noted with the pattern this
week. Afterwards, favored the NWW3 ENP Saturday through Tuesday,
followed by the WAM Tuesday night to match the wind grids.


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


.WARNINGS...Preliminary.

.PZ5 Washington/Oregon Waters...
     None.

.PZ6 California Waters...
.PZZ820...Inner Waters from Point St. George to Point Arena...
     Gale Saturday into Saturday night.
     Gale Possible Sunday into Sunday night.

$$

.Forecaster Reinhart. Ocean Prediction Center.


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