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000
AGPN40 KWNM 290322
MIMPAC

Marine Weather Discussion for N Pacific Ocean
NWS Ocean Prediction Center Washington DC
822 PM PDT Fri Apr 28 2017

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

We will make only a few minor adjustments to the ongoing OPC
forecast for the evening update.

High pressure dominates from Washington and Oregon waters south
and southwestward, with a low pressure trough persisting over
California, per the 00Z NCEP-OPC surface analysis. Gale force
gusts were noted over coastal southern California, where gale
warnings continue into the overnight hours. No headlines are
occurring or currently forecast for the offshore waters during
the next few days, as was forecast earlier. The 18Z GFS is very
similar to the 12Z cycle which was used for the previous
forecast over the region for the next few days. We will continue
to closely monitor PZ5 waters for tomorrow to see if gale
warnings might need to be added to the forecast, with gales
remaining just north of these waters for now, as a cold front
pushes east into the region. For the evening update, we will
make only a few minor tweaks to the previous forecast to fit the
grids and forecast to current conditions, and to nearby coastal
WFO and TAFB forecasts.

As far as sea heights are concerned we will make some adjustment
to the ongoing forecast initially as sea heights are running
slightly higher than the previous forecast over mainly central
and southern California. Overall, no major changes can be
expected for the evening update, with some minor adjustments
initially, and then to fit nearby coastal WFO and TAFB forecast
over the next few days. Sea heights range from near 14 feet off
the southern California coast to around 5 feet over Washington
and Oregon offshore waters, per the latest observations.

-----------------------------------------------------------------
PREVIOUS DISCUSSION...

12z global models in good agreement through most of the forecast
period, with some minor timing differences noted towards the end
of the period. Will lean towards 10m winds from the 12z GFS until
00z Wed, then lean more towards the ECMWF solution thereafter.

Latest ASCAT data showing solid 30 kt over the southern
California offshore waters, with surface observations over the
region showing sustained winds below gale force with some gusts
to 35 kt. Latest global and regional models showing sustained
winds remaining below gale force tonight into Sat as the trough
begins to weaken. Will allow for the gale warning for PZZ840 to
expire on the next package as there is no evidence of sustained
winds to gale force, but may still have some gusts to around
gale force through the evening hours.

Models still in good agreement with low and associated cold front
moving into northern waters Sat and Sat night. Models have low
moving well north of the forecast area, with gales associated
with the low remaining north of the area. The associated cold
front is expected to weaken as it moves across the northern
waters Sat and Sat night and dissipate as it moves into the
northern California waters Sun. Models a little stronger with the
southerly flow ahead of the cold front than in previous runs and
have gales ahead of the front fairly close to the northern
offshore waters on Sat. With models still showing stable
conditions ahead of the front and most of the global models still
showing 10m winds at just below gale force as the front enters
the offshore waters Sat, will keep gales out of the forecast at
this time. But with models trending stronger with the winds ahead
of the front, will need to monitor.

Models are coming into more of agreement with the ridge weakening
over the northern waters Mon and Mon night and allowing a low
pres area to move into the northern waters. Both the GFS and the
UKMET are stronger with the low and even have some winds to 25 kt
associated with it as it moves into the region. Will keep winds
to 25 kt as it enters the waters, but low expected to weaken
quickly late Mon into Mon night.

Ridge then sets up across the northern waters Tue and Tue night
as a cold front approaches. Models begin to differ for Wed and
Wed night as the GFS weakens the ridge faster and allows the cold
front to move into the offshore waters Tue night. Both the ECMWF
and the UKMET hold the ridge long enough to keep the front west
of the offshore waters through the forecast period. Ridges tend
to hold on longer than the models indicate and prefer the
ECMWF/UKMET solution. However, both models are weakening the
ridge, but not as fast as the GFS. Will lean more towards the
ECMWF solution in the wind grids for this portion of the
forecast.


.SEAS...ENP within a foot or two of current observations. Latest
observactions showing seas running 14 to 15 ft over the southern
California offshore waters. Will lean towards 12z ENP for the
wave grids until 00z Wed, then will lean towards the 12z
ECMWFWave solution thereafter.


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



.WARNINGS...Preliminary.

.PZ5 Washington/Oregon Waters...
     None.

.PZ6 California Waters...
     None.

$$

.Forecaster Mills/Achorn. Ocean Prediction Center.


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