Marine Interpretation Message
Issued by NWS
AGPN40 KWNM 241454
Marine Weather Discussion for N Pacific Ocean
NWS Ocean Prediction Center Washington DC
754 AM PDT Fri Mar 24 2017
.FORECAST DISCUSSION...Major features/winds/seas/significant
.weather for the North Pacific N of 30N and E of 150W.
Strong frontal boundary that brought widespread gales to the
northern waters has bowed into the coastal zones as of the 12z
surface analysis - but extends southwest from near Cape Mendocino
and across the central CA offshore zones. Presently winds have
all subsided to below warning threshold, with max ranges in the
20-30 kt range immediately south and southeast of the boundary.
Recent sea state analysis revealed both the WW3/ENP and WAM are
performing quite poorly this morning, but within a limited area
confined to the coastal zones ahead of the front (fortunately not
in the OPC aor). At 12z buoy 46041 - and farther south buoy
46213 - both reporting 15 ft, compared to forecast wave heights
around 10 feet and 12 feet, respectively (3-5 feet below
guidance). Conditions are likely to normalize within the next
couple of hours, however, as seas decay and winds diminish as
the front continues to weaken and push inland.
Sat night into Sun night: good to see the 06z GFS continue to
swing around to a usable solution, very similar to the both the
ECMWF and ensemble means with respect to both timing and
intensity of passing frontal boundary late Sat night and through
the weekend. Save for the UKMET -- now that guidance is
converging on similar solutions, and assuming models remain
consistent, will likely be adding gale headlines with the later
afternoon package across the OR and WA offshore zones. Again,
will await one more 12z cycle before pulling the trigger and
introducing gale headlines.
Mon night onwards: strong pressure gradient still progged
between intensifying low pressure trough along the CA coast and
building EPAC high pressure. Most model guidance has been
consistent building strong prevailing n-nw flow into the 25-30 kt
range. For the past couple of days, the GFS has remained the
most robust solution, signaling a gradient strong enough to
easily support gale force winds. Overnight runs of the GFS backed
off slightly, and shifted core axis of possible gales a little
farther south in basically a 120 nm west semicircle from Point
Conception. No major changes in forecast thinking at this time;
will continue to rely on the more consistent ECMWF solutions, and
continue to monitor latest guidance. At some point, would not be
surprised to add gales into the this portion of the forecast,
whether that be later this afternoon or more of a now cast as the
event draws nearer.
Not much change in the forecast thinking...cold front has pushed
east of the PZ5 waters per the 06z OPC surface analysis w/the
southern end extending across the northern PZ6 waters and a high
pres ridge over the rest of the PZ6 waters. So forecast will
start off w/no warning headlines in place. Weak secondary front
has been handled well by the guidance and is no different in this
00z model package and is expected to pass through the waters
today and tonight. High pressure slides through w/a cold front
nearing the region Sat...then pushing through the waters Sat
night into Sun night. 00z GFS/UKMET/ECMWF have come into better
agreement this run concerning frontal passage timing and
structure though appears the 00z ECMWF/UKMET are still a tad
weaker in regards to pre-frontal winds. Hence will populate
using 00z ECMWF WINDS FROM Sun 12z to Tue 00z and continue to
keep winds at 30 kt for now in the PZ5 waters. Also decided to
hold winds at 30 kt in the n/nw-lies expected over the southern
PZ6 waters Tue in association with inland troughing to the east
interacting w/a high pressure ridge to the west. Confidence in
gales is growing but would want to see at least another run or
two before introducing gales given duration of gales via 00z
GFS/ECMWF are only for 12 hours on so on Tue which is Day 5.
.SEAS...Favored 00z NWW3 winds where 00z GFS was used...00z ECMWF
WAM where 00z ECMWF winds were used.
.EXTRATROPICAL STORM SURGE GUIDANCE...n/a.
.PZ5 Washington/Oregon Waters...
.PZ6 California Waters...
.Forecaster Collins/Holley. Ocean Prediction Center.