Marine Weather for HS 102


marine weather discussion for N Pacific Ocean NWS ocean prediction center Washington DC 822 PM PDT Fri Apr 28 2017

.Forecast discussion...Major features/winds/seas/significant .Weather for the North Pacific N of 30n and E of 150w.

We will make only a few minor adjustments to the ongoing opc forecast for the evening update.

High pressure dominates from Washington and Oregon waters south and southwestward, with a low pressure trough persisting over California, per the 00z NCEP-opc surface analysis. Gale force gusts were noted over coastal Southern California, where gale warnings continue into the overnight hours. No headlines are occurring or currently forecast for the offshore waters during the next few days, as was forecast earlier. The 18z GFS is very similar to the 12z cycle which was used for the previous forecast over the region for the next few days. We will continue to closely monitor pz5 waters for tomorrow to see if gale warnings might need to be added to the forecast, with gales remaining just north of these waters for now, as a cold front pushes east into the region. For the evening update, we will make only a few minor tweaks to the previous forecast to fit the grids and forecast to current conditions, and to nearby coastal WFO and TAFB forecasts.

As far as sea heights are concerned we will make some adjustment to the ongoing forecast initially as sea heights are running slightly higher than the previous forecast over mainly central and Southern California. Overall, no major changes can be expected for the evening update, with some minor adjustments initially, and then to fit nearby coastal WFO and TAFB forecast over the next few days. Sea heights range from near 14 feet off the Southern California coast to around 5 feet over Washington and Oregon offshore waters, per the latest observations.

----------------------------------------------------------------- Previous discussion...

12z global models in good agreement through most of the forecast period, with some minor timing differences noted towards the end of the period. Will lean towards 10m winds from the 12z GFS until 00z Wed, then lean more towards the ECMWF solution thereafter.

Latest ascat data showing solid 30 kt over the Southern California offshore waters, with surface observations over the region showing sustained winds below gale force with some gusts to 35 kt. Latest global and regional models showing sustained winds remaining below gale force tonight into Sat as the trough begins to weaken. Will allow for the Gale Warning for pzz840 to expire on the next package as there is no evidence of sustained winds to gale force, but may still have some gusts to around gale force through the evening hours.

Models still in good agreement with low and associated cold front moving into northern waters Sat and Sat night. Models have low moving well north of the forecast area, with gales associated with the low remaining north of the area. The associated cold front is expected to weaken as it moves across the northern waters Sat and Sat night and dissipate as it moves into the northern California waters sun. Models a little stronger with the southerly flow ahead of the cold front than in previous runs and have gales ahead of the front fairly close to the northern offshore waters on Sat. With models still showing stable conditions ahead of the front and most of the global models still showing 10m winds at just below gale force as the front enters the offshore waters Sat, will keep gales out of the forecast at this time. But with models trending stronger with the winds ahead of the front, will need to monitor.

Models are coming into more of agreement with the ridge weakening over the northern waters Mon and Mon night and allowing a low pres area to move into the northern waters. Both the GFS and the UKMET are stronger with the low and even have some winds to 25 kt associated with it as it moves into the region. Will keep winds to 25 kt as it enters the waters, but low expected to weaken quickly late Mon into Mon night.

Ridge then sets up across the northern waters Tue and Tue night as a cold front approaches. Models begin to differ for Wed and Wed night as the GFS weakens the ridge faster and allows the cold front to move into the offshore waters Tue night. Both the ECMWF and the UKMET hold the ridge long enough to keep the front west of the offshore waters through the forecast period. Ridges tend to hold on longer than the models indicate and prefer the ECMWF/UKMET solution. However, both models are weakening the ridge, but not as fast as the GFS. Will lean more towards the ECMWF solution in the wind grids for this portion of the forecast.

.Seas...Enp within a foot or two of current observations. Latest observactions showing seas running 14 to 15 ft over the Southern California offshore waters. Will lean towards 12z enp for the wave grids until 00z Wed, then will lean towards the 12z ecmwfwave solution thereafter.

.Extratropical storm surge guidance...N/A.


.Pz5 Washington/Oregon waters... None.

.Pz6 California waters... None.


.Forecaster Mills/achorn. Ocean prediction center.

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