000
AGPN40 KWNM 230219
MIMPAC

Marine Weather Discussion for N Pacific Ocean
NWS Ocean Prediction Center Washington DC
619 PM PST Fri Feb 22 2019

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

Low pressure currently northwest of Vancouver island will move
slowly southeast tonight through Saturday night while weakening.
Meanwhile, low pressure is expected to move into the southern pz5
waters by Sunday night. Gales are possible with this system
across the offshore waters, but for now will keep the highest
winds at 30 knots and see what the later model guidance shows.
This low will then move inland Monday. Another low will then move
across the northern pz6 waters by Tuesday with winds as high as
30 knots. Farther south, mainly light winds are expected across
the southern pz6 waters tonight into Wednesday. For wind grids
will continue to use the current grids throughout the forecast
period. Current forecast looks reasonable and will continue to
carry no warnings across the offshore waters during the forecast
period.

For wave height grids will also continue to use the current grids
throughout the forecast period.

Extratropical storm surge guidance...n/a.

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PREVIOUS DISCUSSION...

The Ascat wind retrievals from 17Z and 18Z overpasses this
afternoon show a large area of 20 kt across the offshore waters
with a few small areas of 25 kt along the California coast near
Point Arena and Point Conception as a coastal low pressure trough
interacts with high pressure to the W of PZ5. This is down from
last night where the pressure gradient had been tighter, and the
12Z GFS/ECMWF both indicate that trend will continue as the high
slowly builds E over the offshore waters. Further N, the Ascat
indicates a large area of 25 kt in the inner PZ5 waters near a
cold front currently over the area. The 12Z models agree on this
feature as well, with the GFS/ECMWF indicating the front will
move inland allowing the winds to weaken overnight. The 12Z ECMWF
seems representative when compared with the rest of the 12Z
guidance over the next 24 hours, and is similar to the previous
wind grids. As a result, am planning on starting out with a 75/25
blend of the 12Z ECMWF and previous winds.

On Sun, the 12Z models indicate a shortwave trough will undercut
the ridge in the E Pacific and move into the offshore waters by
Sun night. The GFS has been indicating stronger surface
development of the associated low pressure center as it passes
through the nrn PZ6/srn PZ5 waters late Sun into Sun night, as
the ECMWF/UKMET have been weaker in the offshore zones. However,
the forcing does seem all that impressive, and the 12Z ECMWF and
UKMET maintain max winds at 30 kt in the offshore waters, so
confidence with winds reaching gale force in the offshore waters
is just below average at this point. However, with the
channeling expected to develop between the low and the coast,
winds should be higher in the coastal zones and confidence with
gales developing there is above average. As far as the offshore
winds are concerned, the 12Z ECMWF again seems representative of
the 12Z guidance, so planning on continuing the blend used with
the first 24 hours of the forecast.

The 12Z models then diverge on the next system Tue into Wed,
resulting from the differences of where an upper low cuts off as
another shortwave phases into the trough across the nrn zones.
The GFS has been very inconsistent, and the 12Z run has become a
fast outlier with taking the low inland. The 12Z ECMWF/UKMET/GEM
all keep the low offshore, and this idea is supported by a
relatively strong signal in the 12Z GEFS members. WPC medium
range guidance is also favoring a solution closer to the 12Z
ECMWF, so planning on continuing the previous blend through the
remainder of the forecast period.

.SEAS...The 12Z ECMWF WAM is initialized slightly higher and
better than the 12Z Wavewatch with the latest observational
data, and indicates seas still up near 15 ft in the PZ6 waters
with the remaining cold advection over the area. The models agree
somewhat over the short range, then start differing somewhat
significantly on Sun mainly as the result of the overdone GFS
winds being higher than the ECMWF. Since the wind grids are a
75/25 blend of the 12Z ECMWF winds with the previous grids, am
planning on using a similar blend with the 12Z ECMWF WAM and the
previous wave height grids.

.EXTRATROPICAL STORM SURGE GUIDANCE...n/a.


.WARNINGS...Preliminary.

.PZ5 Washington/Oregon Waters...
None.

.PZ6 California Waters...
None.

$$

.Forecaster Nolt/Kells. Ocean Prediction Center.