North Pacific Marine Weather Discussion

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AGPN40 KWNM 231501
MIMPAC

Marine Weather Discussion for N Pacific Ocean
NWS Ocean Prediction Center Washington DC
701 AM PST Thu Nov 23 2017

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

ASCAT overpasses just after 06z returned several gale force wind
retrievals associated with low pressure just NW of the outer 
Washington offshore waters. Model trends suggest the low begins 
to fill only after about 18z today as the low moves E skirting
the northern OPC zones. Accordingly, plan on adding in a brief
period of gales until 18z as the associated low pressure trough
moves across zone 900, with conditions dropping below warning
criteria as the boundary weakens into zone 800 by 21z. 

Upper ridge begins to shift east by Saturday, as upper trough 
digs southeast from the Gulf of Alaska. Digging shortwave carves 
out a high amplitude, slowly eastward progressing trough over 
the E Pacific late Saturday through Monday. A series of 
shortwaves are expected to round the base of the reloading 
trough and impact the offshore zones during this time. Model 
agreement and even run to run consistency Saturday and beyond 
remains poor at best, but not too unusual during a transition 
season. Accordingly, overall forecast confidence is below 
average. 

For now will continue with previous grids from the night shift,
which after Saturday, are based on a non-NCEP UKMET and ECMWF
solution. Will re-evaluate entirety of forecast with upcoming 
12z model suite. 

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PREVIOUS DISCUSSION...

Gale force winds slated for Saturday will be retained because a
series of troughs and fronts will pass east across the northern
waters. Satellite images show most of the cold cloud across the
northern and central waters. At 06Z, NCEP map has a cold front
across the northern waters that extends from low pressure 992 MB
over Vancouver Island and a trough trough extends southwest from
the same low. High pressure 1022 MB over the southern waters
has extended  its ridge into the southeaster portion of the 
central waters and southern waters. Pressure gradient over the 
central and southern waters is fairly relaxed while over the 
northern waters, pressure gradient is fairly tight where maximum 
winds now just below gale force threshold have been observed. 
Though winds are now diminishing as a trough moves across the 
northern waters it will be quickly followed by a cols front that 
will re-enforce the gradient and allow winds to reach gale force 
strength again. Models GFS/CMC/ECMWFHR/UKMETHR/NAM/NOGAPS/JMA 
have initialized the 06Z surface observations fairly well with 
just small variations mostly on the actual position of the cold 
front and trough to the west of the region. The models are 
generally in good agreement in the short term on building high 
pressure over the southern waters and as low pressure approaches 
the waters form the gulf of Alaska, models agree on tightening 
the pressure gradient again over the northern waters and allow 
winds to increase. In the extended period, models show some 
differences on the position of low pressure that will approach 
from the southwest with GFS being the fastest and UKMETHR being 
the slowest keeping ECMWFHR and CMC in between. GFS brings the 
low into the northern waters while UKMETHR and ECMWFHR keeps it 
over the western edge of the northern waters while CMC weakens it
and keeps it west of the northern waters. Otherwise, models have
a very similar solution apart from timing and track differences.
ECMWFHR is the only model that keeps the winds below gale force.
So either model choice will need some adjustments in the 
extended period. For now will retain the official winds.

.SEAS...peaked at 18 ft over the northeastern portion of the northern
waters and they are relatively high over the rest of the 
northern and central waters. Seas are less than 6 ft over the 
southern waters south of 35N. Both wave models NWW3 and ECMWFWAVE
fit the observed seas pattern well but have differences on the 
actual peak value over the northern waters where NWW3 has a peak 
at 18 ft while ECMWFWAVE peak value is 16 ft. For this issuance 
will continue with NWW3 initially then switch to ECMWFWAVE in the
extended period. 
 


.EXTRATROPICAL STORM SURGE GUIDANCE...



.WARNINGS...Preliminary.

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

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

$$

.Forecaster Collins/Musonda. Ocean Prediction Center.