North Pacific Marine Weather Discussion

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AGPN40 KWNM 171526
MIMPAC

Marine Weather Discussion for N Pacific Ocean
NWS Ocean Prediction Center Washington DC
726 AM PST Sat Feb 17 2018

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

Low pressure just north of the region will move east and high 
pressure will build in from the northwest and will strengthen a 
ridge to the west of the region while a low pressure trough along
the coast will weaken and that will relax pressure gradient over
the region. GOES16 satellite images show low and high clouds 
moving in the same east direction over the northern waters and 
low level divergence is depicted over the central and southern 
waters. NCEP map at 18Z has low pressure 1002 MB 120 NM north of
the Washington waters with a colds front touching the northwest 
portion and warm front touching the northeastern portion of the 
Washington waters. A low pressure trough stretches from southern 
into central California coast. High pressure 1035 MB centered 420
NM west of the northern California outer waters extends a ridge 
into the central and southern waters. Pressure gradient is tight 
over the northern waters but relaxed elsewhere and maximum winds
in the gale force range are over the northern waters. 

Seas range between 6 and 12 ft with lowest seas over the far 
southern waters. Seas currently peak at 15 ft over the northwest 
portion of the washington waters and are building from the 
northwest. NWW3 and ECMWFWAVE models fit well the observed seas 
pattern and have been quite consistent in the previous runs. Will
retain seas from the previous forecast as described below in the
previous discussion section because there have been no major 
changes since the last issuance. 
 
Models in the upper levels have high pressure to the west of the
region that extends a ridge northwest across the Bering sea but 
some energy is trapped in a shallow trough in the Gulf of Alaska 
that will swiftly move southeast into the northern waters in the 
short term. This scenario supports strengthening surface low 
pressure just north of the region. 

The global models GFS/ECMWFHR/CMC/UKMETHR/NAM/NOGAPS/JMA have 
initialized the 12Z surface observations fairly generally well 
but just small variations in the short term on the strength and 
movement. Otherwise the small variations do not alter the general
synoptic features and so will not deviate much from the previous
forecast as described below. 


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PREVIOUS DISCUSSION...

The most recent ASCAT pass shows a strengthening low center NW of
the waters moving SE towards the region. Currently the maximum
winds associated with the system are 45 kt. An ASCAT pass from
06Z indicates winds to 30 kt along the northern California coast.
The most significant effect on the offshore waters will be a
strong short-wave digging SE across the entire waters during the
next 3-4 days, while the associated low center moves SE along the
coast, or just inland. The 00Z global models are in very good
agreement through 00Z Mon, then begin to differ, mainly due the
discrepancy of the forecasted wind speed across the region. The
ECMWF, and to some extend the UKMEt, forecast a more prolonged
event than the GFS does with that system. The GFS is the outlier
in this scenario. For that reason i've decided to populate the
wind grids using the 10/30 GFS through 00Z Mon, then transition
to the ECMWF for the remainder of the period.

Seas...Although the waves from both the ENP and WAM were
initialized well over the waters there are some significant
differences in the days ahead. Generally the WAM is forecasting
higher seas than the ENP throughout much of the forecast. I'm 
not ready to go quite as high as the WAM and therefore will 
populate the wave grids using a 50/50 blend of the ENP/WAM 
through 12Z Wed, then transition to the WAM for the remainder of 
the week.

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


.WARNINGS...Preliminary.

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

.PZ6 California Waters...
.PZZ820...Inner Waters from Point St. George to Point Arena...
     Gale Sunday night.
     Gale Possible Monday into Monday night. 
.PZZ920...Outer Waters from Point St. George to Point Arena...
     Gale Sunday night.
     Gale Possible Monday.
.PZZ825...Inner Waters from Point Arena to Pigeon Point...
     Gale Sunday night.
     Gale Possible Monday into Monday night. 
.PZZ925...Outer Waters from Point Arena to Pigeon Point...
     Gale Sunday night.
     Gale Possible Monday into Monday night. 
.PZZ830...Inner Waters from Pigeon Point to Point Piedras Blancas...
     Gale Possible Monday into Monday night. 
.PZZ930...Outer Waters from Pigeon Point to Point Piedras Blancas...
     Gale Possible Monday.
.PZZ835...Inner Waters from Point Piedras Blancas to Santa Cruz Island, CA...
     Gale Possible Monday night.

$$

.Forecaster Musonda/Shaw. Ocean Prediction Center.