034  
AGPN40 KWNM 210332  
MIMPAC  
 
MARINE WEATHER DISCUSSION FOR N PACIFIC OCEAN  
NWS OCEAN PREDICTION CENTER WASHINGTON DC  
832 PM PDT FRI APR 20 2018  
   
FORECAST DISCUSSION
 
MAJOR FEATURES/WINDS/SEAS/SIGNIFICANT  
.WEATHER FOR THE NORTH PACIFIC N OF 30N AND E OF 150W.  
 
NO SIGNIFICANT CHANGES TO THE FORECAST ANTICIPATED AT THIS TIME  
AS CURRENT FORECAST IN LINE WITH LATEST MODEL CONSENSUS,  
SUPPORTING THE 12Z GFS ON WHICH THE GRIDS ARE BASED. THE GRIDS  
ARE ALSO IN LINE WITH THE LATEST WPC GUIDANCE THROUGH DAY 5. WITH  
THE 18Z GFS CONSISTENT AND SHOWING LITTLE CHANGE, THER IS NO NEED  
TO UPDATE WITH THE NEWER 18Z GUIDANCE.  
 
SEAS...WAVE GRIDS BASED ON 12Z ENP WW3 ARE WITHIN A FOOT OR TWO  
OF CURRENT OBSERVATIONS AND THE 12Z ECMWF WAM, AND WITH NEWER 18Z  
GUIDANCE SHOWING LITTLE CHANGE, NO CHAANGES ARE PLANNED.  
 
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PREVIOUS DISCUSSION...  
 
12Z GLOBAL MODELS IN GOOD AGREEMENT THROUGH THE FORECAST PERIOD.  
FOR THE WIND GRIDS, WILL LEAN TOWARDS THE 12Z GFS THROUGH THE  
PERIOD, AS IT HAS GOOD SUPPORT FROM BOTH THE 12Z ECMWF AND THE  
12Z UKMET.  
 
MODELS IN GOOD AGREEMENT WITH THE TIMING AND STRENGTH OF A COLD  
FRONT CURRENTLY APPROACHING THE NORTHERN WATERS. MODELS SHOWING  
WINDS TO 30 KT IN THE SOUTHERLY FLOW AHEAD OF THE FRONT OVER THE  
PZ5 WATERS TONIGHT, WITH WINDS TO 30 KT CONTINUING IN THE  
WESTERLY FLOW BEHIND THE FRONT LATER TONIGHT INTO SAT. GFS AND  
ECMWF HINTING AT POTENTIAL FOR SOME GALES IN THE WESTERLY FLOW  
BEHIND THE FRONT, BUT KEEP THEM NORTH OF THE AREA. WILL NEED TO  
MONITOR TO SEE IF THESE WINDS DO COME DOWN FAR ENOUGH SOUTH TO  
AFFECT THE OFFSHORE WATERS, BUT FOR NOW WILL KEEP THEM NORTH OF  
THE AREA.  
 
HIGH PRESSURE RIDGE BUILDS ACROSS THE NORTHWEST WATERS SAT AND  
SAT NIGHT, AS A COASTAL TROUGH DEVELOPS ALONG CALIFORNIA AND  
NORTHERN OREGON. NO SIGNIFICANT CHANGES IN THE MODELS AS THEY DO  
HINT AT A PERIOD OF GALES IN THE COASTAL WATERS SAT NIGHT, AND  
AGAIN LATE SUN INTO SUN NIGHT. QUESTION IS WHETHER THESE GALES  
EXTEND OUT FAR ENOUGH TO THE WEST TO AFFECT THE ADJACENT OFFSHORE  
WATERS. AGAIN, THE BEST CHANCE FOR ANY GALES IN THE OFFSHORE  
WATERS IS SAT NIGHT, AND WILL CONTINUE WITH SOME GALES IN THE  
NORTHEASTERN PORTION OF PZZ820 FOR SAT NIGHT, IN LINE WITH THE  
ADJACENT COASTAL OFFICES. FOR LATE SUN INTO SUN NIGHT, GALES LOOK  
TO BE CONFINED TO THE COASTAL ZONES AND WILL LEAVE WINDS TO 30 KT  
FOR NOW. CONFIDENCE IN GALES FOR THE OFFSHORE WATERS SAT NIGHT IS  
LOW, WITH THE BEST CHANCE FOR GALES DURING THIS TIME FRAME BEING  
THE COASTAL WATERS. WILL BOOST 10M GFS WINDS BY 10 PERCENT OFF  
THE NORTHERN CALIFORNIA COAST SAT NIGHT TO KEEP GALES IN THE  
FORECAST.  
 
RIDGE SLOWLY WEAKENS SUN THROUGH MON NIGHT, THEN REBUILDS  
NORTHWEST OF THE AREA TUE AND TUE NIGHT. MEANWHILE, COASTAL  
TROUGH STRENGTHENS SOMEWHAT ALONG THE OREGON COAST, WITH WINDS TO  
25 KT EXPECTED. TROUGH THEN MOVES OFFSHORE WED AND WED NIGHT.  
   
SEAS
 
WAVE GUIDANCE WITHIN A FOOT OR TWO OF CURRENT  
OBSERVATIONS. FOR THE WAVE GRIDS, WILL LEAN TOWARDS THE 12Z ENP  
GUIDANCE THROUGH THE FORECAST PERIOD.  
   
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 SATURDAY NIGHT.  
 

 
 
.FORECASTER BANCROFT/ACHORN. OCEAN PREDICTION CENTER.  
 
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