Marine Interpretation Message
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035
AGPN40 KWNM 171537
MIMPAC

Marine Weather Discussion for N Pacific Ocean
NWS Ocean Prediction Center Washington DC
737 AM PST Wed Jan 17 2018

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

12Z NCEP surface analysis places strong low pressure with 965 mb
center west of the area near 45N 141W with last ASCAT-B pass from
0722Z showing hurricane-force winds just south of the center.
Latest surface observations support widspread southerly gales
over the waters from the NW part of the northern PZ6 offshore
waters northward, and storm force in the more channeled flow
ahead of an approaching warm front just north of the waters.

Latest models are in best agreement into Fri night and the
current griods look fine. After Fri night the models develop some
differences with 06Z GFS and 00Z ECMWF supporing a somewhat
slower passage of the next strong frontal system to pass through
the waters from northern PZ6 waters northward with 00Z UKMET
closer to present grids for Sat into Sun, but plan no changes at
this time.

Seas...Updated the wave grids with the 00Z ECMWF WAM for the
first period as that model initializes best against the 12z sea
state analysis, before reverting to the previous wave grids
tonight and beyond, when no changes were made to assicoated wind
grids.

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

Low pressure is on track to pass to the west of the region and
associated fronts will sweep across the northern and central
waters while high pressure ridge will still persist over the
southern waters. Pressure gradient will continue to be tight as a
series of fronts will pass across the northern and central
waters while a relaxed pressure gradient will still be confined
to the far southern waters through most of the forecast period.
GOES16 RGB Geocolor satellite images still show massive clouds,
associated with developing low to the west of the waters now 540
NM west of the Oregon waters that is moving northeast. Low level
diffluence is still depicted over the southern waters. At 06Z,
NCEP weather map has high pressure 1025 MB just west of the
southern waters that still extends a weak ridge across the
southern waters while low pressure has deepened to 967 MB, with
hurricane force winds in its southern sector, west of the central
waters and its warm front stretches southeast across the
Washington and Oregon waters. Another low pressure 977 MB with
gale force winds is in the Gulf of Alaska. Farther west is still
high pressure 1031 MB due far northwest of the Hawaiian Islands
near the dateline north of 30N that extends a strong ridge north
into the Bering sea. More low pressure systems are west of the
high pressure ridge above. In the short term, low pressure west
of the waters will keep deepening as it moves northeast and its
associated fronts will move across the waters forcing a tighter
pressure gradient that will elevate winds to storm force
threshold over the western portion of the north waters while high
pressure will remain in the same vicinity and help to keep
elevated winds confined to the central and northern waters. Low
pressure in the gulf of Alaska will slowly move northwest as it
weakens. In the extended period, a series of high pressure
centers will be tracking east and will remain to the south of 40N
allowing more active weather north of 40N. As such, a prolonged
tight pressure gradient will be maintained by a series of low
pressure systems that will pass over the central and northern
waters.

Global models GFS/CMC/ECMWFHR/UKMETHR have initialized the 00Z
surface observations with very small variations. However, models
have some differences especially on the wind speed and also the
areal coverage of the winds in warning threshold. In the short
term, GFS and CMC have winds reaching storm force in the waters
while UKMETHR and ECMWFHR only have winds in the gale force
range. ECMWFHR is the only model among the 4 that has less than
hurricane force winds with the low at 00Z. GFS and CMC have
slightly higher winds than UKMETHR. Scatterometer pass at 0624Z
just missed the region of interest but earlier pass had some 70
Kt wind barbs and considering that the system is still
developing, winds must be at least in the 70 kt range and so will
stay with GFS that has continued to depict a good handle on this
system.

.SEAS...Seas are still relatively large across the region ranging
between 12 and 18 ft with a peak at 20 ft over the Oregon and
Northern California outer waters and they are building. Currently
the peak value is 45 ft near 38N144W. NWW3 and ECMWFWAVE models
continue to fit fairly well the observed seas pattern but there
are still small differences on the actual peak values. NWW3 has
maintained the match for both peak values over the forecast
waters and the high seas with the impending low while ECMWFWAVE
is still underdone by 2 ft over the waters and 3 ft over the high
seas. Both wave models have continued to be quite consistent
which makes it easier to apply any correction factor depending on
the wave model choice. The low will still develop more and seas
should keep on building and so will continue with NWW3 and will
stay close to the prevailing seas grids.


.EXTRATROPICAL STORM SURGE GUIDANCE...Storm surge around 9/10 is
expected along the Canada coast and but will be less over the
Oregon and Washington coasts with a peak on Thursday.


.WARNINGS...Preliminary.

.PZ5 Washington/Oregon Waters...
.PZZ800...Inner Waters from Cape Flattery to Cape Shoalwater...
     Gale today into Thursday night.
     Gale Possible Friday night into Saturday.
     Gale Possible Sunday.
.PZZ900...Outer Waters from Cape Flattery to Cape Shoalwater...
     Gale today.
     Storm tonight into Thursday.
     Gale Thursday night.
     Gale Possible Friday into Friday night.
     Gale Possible Sunday.
.PZZ805...Inner Waters from Cape Shoalwater to Cape Lookout...
     Gale today into Thursday night.
     Gale Possible Saturday into Sunday.
.PZZ905...Outer Waters from Cape Shoalwater to Cape Lookout...
     Gale today.
     Storm tonight into Thursday.
     Gale Thursday night.
     Gale Possible Friday into Saturday.
     Gale Possible Sunday.
.PZZ810...Inner Waters from Cape Lookout to Florence OR...
     Gale today into Thursday.
     Gale Possible Saturday.
     Storm Possible Saturday night.
     Gale Possible Sunday.
.PZZ910...Outer Waters from Cape Lookout to Florence OR...
     Gale today into Thursday night.
     Gale Possible Friday.
     Gale Possible Saturday.
.PZZ815...Inner Waters from Florence OR to Point St. George...
     Gale today into tonight.
     Gale Possible Saturday.
     Storm Possible Saturday night.
     Gale Possible Sunday.
.PZZ915...Outer Waters from Florence OR to Point St. George...
     Gale today into Thursday night.
     Gale Possible Friday.
     Gale Possible Saturday into Saturday night.

.PZ6 California Waters...
.PZZ820...Inner Waters from Point St. George to Point Arena...
     Gale today.
     Gale Possible Saturday night into Sunday.
.PZZ920...Outer Waters from Point St. George to Point Arena...
     Gale today into tonight.
     Gale Possible Saturday into Sunday.
.PZZ825...Inner Waters from Point Arena to Pigeon Point...
     Gale Possible Sunday into Sunday night.
.PZZ925...Outer Waters from Point Arena to Pigeon Point...
     Gale Possible Sunday.

$$

.Forecaster Bancroft/Musonda. Ocean Prediction Center.



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