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000
AGPN40 KWNM 220210
MIMPAC

Marine Weather Discussion for N Pacific Ocean
NWS Ocean Prediction Center Washington DC
610 PM PST Tue Feb 21 2017

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

A relatively weak (generally 15-20 kt, or less) NWly gradient
persists throughout all of the coastal/offshore waters at the
moment. Max seas throughout are likely in the low teens, highest
across the outer Nrn/central PZ6 waters, which are being handled
slightly better by the 18Z Wavewatch III versus the 12Z ECMWF
WAM.

Over the short term, in response to a high pressure ridge
forecast to build W of the offshore waters and a series of upper
level short wave troughs diving SE into the Wrn conus causing
lower pressures, the models all forecast the NWly gradient to
strengthen, especially across the central/Srn PZ6 waters Wed
night into Thu night. The previous forecast package used
primarily 12Z GFS first sigma level winds for this gradient and
kept winds subgale. So with the 18Z NAM/GFS remaining consistent
with these forecast winds and the 12Z UKMET/ECMWF forecasting
slightly weaker gradients do not plan on making any major short
term changes in the next offshore forecast package.

In the long range, would favor a solution close to the similar
18Z/12Z GFS and 12Z ECMWF for a weak surface low (with max winds
up to 20-25 kt) to track S across the PZ5 waters late Fri into
Sat, then dissipating. Will just make some minor additional edits
to the previously populated 12Z GFS winds for this system. Then
as noted earlier, the disparity between the latest global models
increases significantly Sat night into Sun night in regards to a
potentially strong surface low tracking E into the PZ6 waters.
Versus its previous 12Z run, the 18Z GFS remains consistent in
forecasting a strong low to track E across the central PZ6 waters
Sun into Sun night with widespread gale force associated winds.
If anything the 18Z GEFS Mean indicates that the 18Z GFS may be
too fast with its forecast low. The 12Z ECMWF looks like a weak
outlier solution for this system while the 12Z UKMET, which is
similar to the 18Z/12Z GFS, looks like a slow outlier. Therefore
since its most in line with the latest WPC Medium Range guidance
will stay the course the previously used 12Z GFS solution and
will just make some minor additional edits in deference to the
18Z GFS.



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

A large swath of ASCAT data is missing across the offshore waters
on the latest pass...between 130w and 135w the winds are light
5-15 kt. The most recent satellite picture indicates a short-
wave west of the California waters moving east...expected to turn
southeast while remaining w of the region over the next 36 hrs.

The 12z global models are in very good agreement during the next
72 hours...then begin diverge days 4-7. There will be two main
problem areas over the next 7 days. The first chance of gale
conditions will occur over the favored area near the channel
islands across the southern California waters Thursday into
Thursday night. Both the GFS and ECMWF are indicating the gales
are possible...with GFS 30M winds forecasting max winds near 35
kt. The ECMWF is also showing a small area of 30 kt winds. At
this time I will maintain continuity and keep gales out of the
offshore waters...while also matching with the southern coastal
zones. The biggest forecast problem will occur later in the
period...Saturday into Sunday night. The GFS and ECMWF have
essentially switched solutions since yesterday at this time.
Yesterday the GFS was the outlier model...while all of the other
global models were in decent agreement. The GFS switched
solutions with the 00z last night to a stronger...ECMWF
solution...therefore gales were issued. The 12z GFS run from
today is consistent with the previous run...indicating that the
southern stream will phase with the northern stream bringing a
strong area of low pres across the California waters...although
about 12 hours slower than previous runs. The 12z ECMWF did not
phase the two systems however and therefore forecasts a much
weaker system eventually moving into the California waters. I
will try and keep as much continuity as possible from the last
couple of forecasts and populate the wind grids using the GFS
throughout the period..and the 30M winds during periods of
instability. I will also cap the max winds at 40 kt for late in
the week.

Seas...Both the ENP and WAM initialized well across the waters.
During the first couple of days the WAM indicates higher waves
possible in the southern waters in areas of higher winds...the
ENP is likely too weak in that region. I will populate the wave
grids using a 50/50 blend of the two models through 00z
Saturday...then transition to 100 percent ENP thereafter.

.EXTRATROPICAL STORM SURGE GUIDANCE...N/A.


.WARNINGS...Preliminary.

.PZ5 Washington/Oregon Waters...
     None.

.PZ6 California Waters...
.PZZ820...Inner Waters from Point St. George to Point Arena...
     Gale Possible Saturday night into Sunday night.
.PZZ920...Outer Waters from Point St. George to Point Arena...
     Gale Possible Saturday night into Sunday night.
.PZZ825...Inner Waters from Point Arena to Pigeon Point...
     Gale Possible Saturday night into Sunday night.
.PZZ925...Outer Waters from Point Arena to Pigeon Point...
     Gale Possible Saturday night into Sunday night.
.PZZ830...Inner Waters from Pigeon Point to Point Piedras Blancas...
     Gale Possible Saturday night into Sunday night.
.PZZ930...Outer Waters from Pigeon Point to Point Piedras Blancas...
     Gale Possible Saturday night into Sunday night.
.PZZ835...Inner Waters from Point Piedras Blancas to Santa Cruz Island, CA...
     Gale Possible Saturday night into Sunday night.
.PZZ935...Outer Waters from Point Piedras Blancas to Santa Cruz Island, CA...
     Gale Possible Saturday night into Sunday night.

$$

.Forecaster Vukits/Shaw. Ocean Prediction Center.



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