Marine Interpretation Message
Issued by NWS
AGPN40 KWNM 090336
Marine Weather Discussion for N Pacific Ocean
NWS Ocean Prediction Center Washington DC
736 PM PST THU DEC 8 2016
.FORECAST DISCUSSION...Major features/winds/seas/significant
.weather for the North Pacific N of 30N and E of 150W.
The latest IR satellite picture shows fairly cloudy skies across
the central regions but clearing over the north waters while
almost clear skies are over the southern waters. The lightning
density map has no indication of TSTMS over the forecast region
and the SREF model has PROB 0 for severe TSTMS across the region
but increses to PROB 10 over the far norh waters FRI night. The
latest observations including earlier scatterometer pass indicate
higher winds over the north waters with maximum in the mid gale
force range. At 00z the NCEP map has low pressure 992 mb near 50N
140W that has an occludded front stretching SE into the north
waters then continues Se as a warm front while its cold front
stretches SW to pass through the central region inline with the
satellite imagery. The winds in the south sector of the low
pressure will increase and reach storm force threshold. The
southern waters are dominated by high pressure 1025 mb centered
just SW of the south waters. Farther west near 42N 164E is low
pressre 980 mb with hurricane force winds while high pressure 1032
mb is near the central pacific. Meanwhile, the pressure gradient
over the forecast waters is fairly slack over most of the region
except the far north waters. The largest seas are over the NW part
of WA waters with peak at 13 ft. Saes are smallest over the far
south waters where they range between 2 and 4 ft. Both NWW# and
ECMWFWAVE models fit very well with the observed seas pattern and
they have been quite consistent in the previous runs. The wave
models are in a good agreement over the short term on building the
seas over the north waters. A blend of both wave models was used
in the previous forecast and the plan is not to deviate from that
solution for this update.
In the upper levels the models GFS/CMC/ECMWFHR/UKMETHR suggest a
band of energy stretches SE from an upperlevel low near 50N 150W
into the north waters. a weak upperlevel ridge with little to no
energy covers the central and southern waters. In the short term
there will be lingering enregy over the north waters that will
keep a tight presssure gradientand that will persist into the
The 18Z models GFS/CMC/NOGAPS/UKMETHR/ECMWFHR have initialized
the 00Z surface observations fairly well and they continue to be
in agreement in the short term on pushing low pressure from the NW
toward the north waters. Will stay with mostly GFS in the short
term and part of the extended period. Will switch to ECMWFHR in
the last 2 periods.
The 12Z models and ensembles are in very good agreement across
the east Pacific over the next few days. There are some minor
detail differences between the models with the surface low
forecast to pass just north of the PZ5 waters Friday night and
Saturday along with the southward extent of the associated gales
across these waters. First though the east to southeast gales
will continue across the northern PZ5 waters north of the warm
front. An 1830Z Ascat overpasss confirmed 30 to 35 kt across the
outer PZZ900 waters with data over adjacent zones either missing
or very limited. With negative low level static stabilities
offshore north of the warm front and then with some channeling
expected across the far northern portions of the PZ5 waters as
the front approaches Vancouver Island...am favoring the slightly
higher GFS first sigma level winds tonight. Then as the surface
low passes just north Friday night and Saturday am choosing to
use a 50/50 blend of the 12Z GFS and 12Z NAM which will
generally keep continuity with the gale warnings. As noted above
models differ with how far south westerly gales will extend with
previous runs of GFS as well as the 12Z NAM further south than
12Z GFS/UKMET/ECMWF. The blended winds offer a compromise for
these differences...and will include gales across the zones
north of Cape Lookout Friday night and Saturday.
12Z models then all indicate that a second weaker low will track
east across the PZ5 waters toward Cape Shoalwater Sunday into
MOnday. The 12Z GFS looks to have a reasonable handle on this
system and is supported by the 12Z UKMET...with the 12Z ECMWF
slightly north of the above consensus with the track. As this
low weakens and dissipated along the coast near the Columbia
River guidance agrees that a low pressure trough will develop
along the Washington and Oregon coasts late Monday and persist
near the coast through Wednesday night.
Across the PZ6 waters the 12Z models offer differences with the
developing low forecast to move east along a stationary front
Friday night and Saturday. The 12Z GFS appears a bit too strong
with the associated winds to 25 kt and the favored GFS/NAM blend
keeps winds at 20 kt across the central California waters which
is in line with the 12Z ECMWF and 12Z UKMET. Models share the
idea that the cold front should wash out as it moves south off
the southern California coast late Sunday and Sunday night.
Model solutions diverge somewhat next week as an upper level
trough drops south across the offshore waters and interacts with
a series of upper shortwaves progressively passing east
northeast toward and across the PZ5 waters. Beginning Tuesday
used an even blend of the past two runs of the ECMWF which
supports a warm front drifting north across the PZ5 waters. With
forecast confidence diminishing this blend is also a
conservative approach in limiting winds to 20 kt or 25 kt at
.Seas...Wave heights along the Oregon and northern California
coasts are running 3 to 5 ft higher than the Wavewatch III this
afternoon with the 12Z ECMWF WAM much better initialized. For
this reason continued with a 75% 12Z ECMWF WAM/25% 12Z Wavewatch
III blend through Friday...before transitioning solely to the
12Z WW3 Fri night Monday. Then with preference for ECMWF early
next week went back to populating with the above blend.
Extratropical storm surge guidance...N/A.
.PZ5 Washington/Oregon Waters...
.PZZ800...Inner Waters from Cape Flattery to Cape Shoalwater...
Gale Possible Saturday night.
.PZZ900...Outer Waters from Cape Flattery to Cape Shoalwater...
Gale Friday night into Saturday.
.PZZ805...Inner Waters from Cape Shoalwater to Cape Lookout...
.PZZ905...Outer Waters from Cape Shoalwater to Cape Lookout...
Gale Friday night into Saturday.
.PZZ810...Inner Waters from Cape Lookout to Florence OR...
.PZZ910...Outer Waters from Cape Lookout to Florence OR...
.PZZ915...Outer Waters from Florence OR to Point St. George...
.PZ6 California Waters...
.Forecaster Musonda/Clark. Ocean Prediction Center.