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000
AGPN40 KWNM 280342
MIMPAC

Marine Weather Discussion for N Pacific Ocean
NWS Ocean Prediction Center Washington DC
842 PM PDT Thu Apr 27 2017

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

At 00Z high pressure was to the W of the WA/OR waters and also to
the W of the central and srn CA waters. There was weak low near
the wrn areas of the nrn CA waters which should dissipate later
tonight while drifting E. Strongest winds this evening were over
the central and srn areas of the CA waters where observed winds
were at least to 30 kt from a nearby buoy, although marginal
gales may be over the ern areas of the Santa Cruz Island to San
Clemente Island. Have not seen any recent satellite derived winds
over this area nor any ship observation to confirm strength of
winds to gales, although likely will see something later
overnight. The strongest winds in this area tonight should
diminish to subgale on Fri.  On Sat and Sat night models are in
better agreement than last night with close agreement on having
low pressure passing N of the WA waters and moving a cold front
across the waters. The GFS/GEM are stronger with winds in advance
of the front compared with the UKMET/ECMWF. Will continue to
have winds to 30 kt as the cold front weakens while moving E over
the WA/OR waters.

For the updated forecast will stay with prior grids with no
changes for now.

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

12z global models continue to be in good agreement over the
offshore waters through most of the forecast period. Will lean
towards 10m winds from the GFS for the wind grids through the
period.

Coastal trough along the central and southern California coast is
interacting with building east pac high to the northwest and
producing enhanced northerly winds along portions of the central
and southern California coast. Latest surface observations
showing sustained winds around 30 kt with gusts nearing gale
force. As with several past runs, GFS showing gales at 30m but
for the most part keeps 10m winds below gale. However, GFS does
show a few 10m gales in zone PZZ840 late tonight into Friday.
This does have support from both the ECMWF and the UKMET which
does show a few gales at 10m. Continued thinking is that 30m
winds are overdone as these winds will have a hard time mixing to
the surface as sustained winds with a stable atmosphere in place.
However, trying to maintain some continunity with the previous
forecast, will go ahead and keep gales in the forecast from
issuance time through 18z Fri, but limit sustained gales to zone
PZZ840 where there is the greatest chance of seeing gale
conditions. For the remainder of the southern Califorina offshore
waters, will limit winds to 30 kt, but can not rule out a few
gusts to gale force during this time period. Gradient begins to
slowly relax later Fri and Fri night with winds falling below
gale force at that time.

GFS and ECMWF are still on track with low and associated cold
front to impact the northern waters Sat and Sat night. UKMET
looks to have trended further north with its track, but is still
further south than both GFS and ECWMF. GFS and ECMWF showing
strong low pressure moving north of the area, with any gales
associated with the system remaining north of the offshore
waters. As for the associated cold front, models continue to show
front weakening as it moves southeast across the northern waters
late Sat and Sat night as it interacts with the ridge to the
southeast. Front expected to dissipate as it enters the northern
PZ6 waters Sun.

High pressure then rebuilds northwest of the PZ6 waters late Sun
and persists through the remainder of the forecast period. This
high is expected to interact with a intensifying low pressure
trough along the northern and central California coast and
enhance the northerly winds offshore once again. Looks like any
gales associated with this pattern will remain in the coastal
waters, but the UKMET did produce a 35 kt 10m wind offshore
around 06z Mon, with both the GFS and the ECMWF keeping 10m winds
just below gale force in the offshore waters. Will continue to
cap winds at 30 kt for this forecast, but will need to monitor
over the next day or so for strengthening trends.

Prefer GFS/ECMWF trend of weakening or keeping potential low
pressure northwest of the area Sun night into Mon as ridge seems
to be taking hold of the region. Would not be surprised to see
either a weaker trend or a further northwest trend with this
system in the next few runs.

.SEAS...ENP within a foot or two of current observations. Latest
ENP and ECMWFWave in good agreement through the forecast period.
Will lean towards 12z ENP in latest wave grids.


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



.WARNINGS...Preliminary.

.PZ5 Washington/Oregon Waters...
     None.

.PZ6 California Waters...
.PZZ840...Inner Waters from Santa Cruz Island, CA to San Clemente Island, CA...
     Gale tonight into Friday.

$$

.Forecaster Rowland/Achorn. Ocean Prediction Center.



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