Marine Interpretation Message
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000
AGPN40 KWNM 230333
MIMPAC

Marine Weather Discussion for N Pacific Ocean
NWS Ocean Prediction Center Washington DC
833 PM PDT Mon May 22 2017

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

For the evening update updated the near term grids with the
current representative 18Z GFS for tonight and Tuesday modified
using a tool that places first sigma level winds in unstable
areas and 10m winds in stable areas which closely matches current
conditions and the earlier ASCAT passes.

Latest models are otherwise in agreement moving a low pressure
area east from the Gulf of Alaska inland over western Canada
within 24 hours while an associated cold front sweeping SE across
the PZ5 and northern PZ6 waters Tuesday into Tuesday night while
lower pressure prevails inland areas. More significantly the east
Pacific upper ridge and associated surface ridge build strongly
east into the PZ5 waters behind the front and the cold advection
behind the front produces areas of negative static stability.
After Tuesday with the more current GFS showing little change the
previous GFS on which the current grids are based looks
reasonable and supported by other guidance and do not need to be
repopulated. The GFS especially and also the 12Z ECMWF/UKMET/GEM
show a strong signal for northerly gales developing in an area
mainly the inner waters and adjacent coastal waters late Tuesday
and especially Tuesday night and lasting into Thursday. Have only
average confidence that the gales when fully developed will
expand into the outer waters of Point St. George to Point arena
as currently headlined.

Seas...Since the previous shift used the 12Z ECMWF WAM for seas
both currently and forecast and look representative and well
initialized against the 00Z regional sea state analysis and since
the ECMWF is preferred with its more aggressive building of the
seas in the gale area versus the 12Z/18Z NWW3 will leave these
grids in place.
-----------------------------------------------------------------
PREVIOUS DISCUSSION...

Gale warnings will still be retained beginning Tuesday night
over the central and north waters and seas will also build and
peak at 20 ft over the central waters. Chance of rain and areas
of fog with visibility occasionally less than 1 NM mainly over
the central and north waters in the next 48 hours. The satellite
images continue to show anticyclonic circulation center just west
of the north waters and some clouds with cold tops are still
depicted over the far north waters. The latest observations
including scatterometer passes about 1810Z still show higher
winds, though diminishing, over the southeast Oregon waters. The
1800Z NCEP map still has high pressure 1028 MB west of Oregon
waters while an inland trough that runs through several low
pressure centers stretches northwest from New Mexico and then
near the coast areas from the southern California into south
Washington. The pressure gradient has relaxed is just tight over
the central waters. Farther west is mainly high pressure now 1036
mb centered near 40N170W that has dominated the central pacific
ocean with low pressure areas confined to the north of the high
pressure and stretches from the sea of Okhotsk through the Bering
sea into the Gulf of Alaska.

The models GFS/CMC/UKMETHR/ECMWFHR in the upper levels suggest
persistence of upper level ridge over the region that will
confine most of the energy just north of the region. However,
when the energy shifts inland, it will dip down and enhance the
inland trough that will result in a tighter pressure gradient
over the central waters especially the eastern portion and so
will keep the gale warnings in the forecast.

The models GFS/CMC/ECMWFHR/UKMETHR/NOGAPS/NAM at the surface
have generally initialized well again at 1800Z and the minor
differences are still within 2 MB mainly on the central pressure
value of the high pressure just west of the region. The models
have also continued to be in good agreement in the short term on
pushing southwest the center of the high pressure that will
eventually dissipate allowing the inland trough to shift west
into the waters as it deepens. The trough will strengthen as the
main high pressure over the central pacific moves east while
strengthening too. The resultant pressure gradient over the
region will allow winds to be elevated to gale force mainly over
the central waters. The models just differ on the strength of the
winds with GFS and CMC being more aggressive. UKMETHR is very
close to the GFS and CMC solution but just areal coverage of the
gales is smaller whereas ECMWFHR is weaker and covers a much
smaller area of gales. GFS will be used as the main guidance for
winds.

.SEAS...The seas are quite small across the region with a peak
only at 8 ft over the central waters. The wave models NWW3 and
ECMWFWAVE have both initialized well at 1800Z and both models
have been quite consistent in the previous runs. In the short
term the models agree on building seas over the central waters to
peak about 19 ft. NWW3 is slightly weaker than ECMWFWAVE
especially in areas with higher winds and so will therefore stay
close to the ECMWFWAVE guidance.

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


.WARNINGS...Preliminary.

.PZ5 Washington/Oregon Waters...
.PZZ800...Inner Waters from Cape Flattery to Cape Shoalwater...
     Gale Possible Wednesday night.
.PZZ815...Inner Waters from Florence OR to Point St. George...
     Gale Tuesday night into Wednesday.
     Gale Possible Wednesday night.

.PZ6 California Waters...
.PZZ820...Inner Waters from Point St. George to Point Arena...
     Gale Tuesday night into Wednesday.
     Gale Possible Wednesday night into Thursday.
.PZZ920...Outer Waters from Point St. George to Point Arena...
     Gale Wednesday.
     Gale Possible Wednesday night.

$$

.Forecaster Bancroft/Musonda. Ocean Prediction Center.



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