355
AGPN40 KWNM 281524
MIMPAC
MARINE WEATHER DISCUSSION FOR N PACIFIC OCEAN
NWS OCEAN PREDICTION CENTER WASHINGTON DC
824 AM PDT WED APR 28 2021
FORECAST DISCUSSION
MAJOR FEATURES/WINDS/SEAS/SIGNIFICANT
.WEATHER FOR THE NORTH PACIFIC N OF 30N AND E OF 150W.
A HIGH PRESSURE RIDGE WAS OVER THE CENTRAL AND NORTHERN AREAS OF
CA WATERS AND EXTENDED NE OVER THE OR WATERS, THEN INLAND. A WEAK
COASTAL TROF WAS ALONG MOST OF CA THIS MORNING. WINDS ARE LIGHT
THROUGHOUT MOST AREAS OF THE OFFSHORE WATERS AT 15 KT OR LESS
THIS MORNING AND PERSIST INTO THU. BY LATER IN THE WEEK LATE FRI
INTO SAT WINDS STRENGTHEN ALONG THE INNER CENTRAL AND SOUTHERN CA
WATERS TO 25 KT WITH STRONGER WINDS TO 30 KT BY LATER SAT INTO
SUN AS HIGH PRESSURE BUILDS IN FROM THE W AND NW OF THE CA
WATERS. FOR THE MORNING UPDATE WILL STAY WITH PRIOR GRIDS WHICH
LOOK FINE WITH NO NEEDED ADJUSTMENTS FOR NOW.
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PREVIOUS DISCUSSION...
HIGH LATITUDE BLOCKING IS LEADING TO AN AMPLIFIED PATTERN ACROSS
MUCH OF THE MID-LATITUDES WITH A STRONG STORM SYSTEM NEAR
KAMCHATKA AND THE WESTERN ALEUTIANS HELPING TO FURTHER AMPLIFY
THE DOWNSTREAM PATTERN. THE GOES-W AIR MASS RGB SHOWS A DEEP
TROUGH AND CLOSED UPPER-LOW OVER THE NORTHERN GULF OF CALIFORNIA,
WHILE RIDING CONTINUES TO AMPLIFY NORTHWARD INTO SOUTHERN
BRITISH COLUMBIA. THE 06 UTC NCEP SURFACE ANALYSIS SHOWS TWO 1025
MB HIGHS STRETCHING FROM THE CENTRAL OUTER CALIFORNIA WATERS UP
TO THE NORTHERN COASTAL OREGON WATERS. A TROUGH CONTINUES TO SET
UP ALONG THE CENTRAL CALIFORNIA VALLEY HELPING TO KEEP BREEZES OF
UP TO 25 KT RELEGATED CLOSE TO THE NORTHERN AND CENTRAL
CALIFORNIA COAST. THE GOES-W NIGHTTIME MICROPHYSICS RGB SHOWS
MOSTLY CLEAR SKIES ACROSS THE PZ6 WATERS EXCEPT FOR THE OUTER
EDGES OF THE OUTER WATERS WITH HIGH AND MID-LEVEL CLOUDS
STREAMING ACROSS THE NORTHERN PZ5 WATERS IN ASSOCIATION WITH WARM
ADVECTION IN THE VICINITY OF A WARM FRONT.
OVER THE NEXT 48 HOURS, THE SURFACE HIGH OVER THE CENTRAL OUTER
PZ6 WATERS WILL STRENGTHEN TO ~1028 MB, THEN START TO MOVE SW AND
BECOME THE MAIN STEERING FLOW W OF THE PZ6 WATERS THROUGH THE
EXTENDED. MEANWHILE, A COLD FRONT WILL MOVE THROUGH THE PZ5 AND
NORTHERN PZ6 WATERS THU NIGHT THROUGH SAT MORNING. OUTSIDE OF
SOME SHOWERS, GRADIENT WINDS WILL INCREASE TO 25-30 KT AHEAD OF
THE FRONT IN THE OUTER PZ5 WATERS, BUT WEAKEN AS THE FRONT SLOWS
AND WEAKENS HEADING SE. FROM SAT NIGHT THROUGH SUN NIGHT, THE
FRONT WILL BE MOVING THROUGH THE REST OF THE PZ6 WATERS WITH
LITTLE FANFARE, WHILE SURFACE RIDGING REASSERTS ITSELF OVER THE
PZ5 AND NORTHERN PZ6 WATERS. WITH TROUGHING NEAR OR JUST INSIDE
COASTAL CALIFORNIA, N-NW WINDS WILL INCREASE TO 20-30 KTS, BUT
NOT EXPECTING GALES AT THIS TIME.
ANOTHER FRONT APPROACHES THE PZ5 WATERS MON AND WILL E OF THE
AREA MON NIGHT, WHILE THE SOUTHERN PORTION OF THE FRONT
DISSIPATES OVER THE NORTHERN PZ6 WATERS. ANOTHER SURFACE HIGH
MOVES INTO AREA BEHIND THE FRONT WITH THE TROUGH OVER CALIFORNIA
STRENGTHENING A BIT, POSSIBLY LEADING TO GALES CLOSER TO THE
COAST. THE NEXT LOW AND ATTENDED FRONTS APPROACH THE PZ5 WATERS
TUE NIGHT INTO WED.
THE 00 UTC GUIDANCE SUITE IS IN REALLY GOOD AGREEMENT THROUGH SAT
WITH SLIGHT DIFFERENCE FOR SUN WITH THE PLACEMENT OF A WEAKENING
LOW THAT SHOULD STAY JUST NORTH OF THE PZ5 WATERS. MEANWHILE, ALL
GUIDANCE HANDLE THE NEXT TWO FRONTS WELL WITH MINOR TIMING
DIFFERENCES. FOR THESE REASONS, THE GFS WILL BE USED THROUGH SAT,
THEN A BLEND OF THE GFS/EC WILL BE USED FOR THE REMAINDER OF THE
FORECAST.
SEAS
CURRENT SEAS OF 4-8 FT IN THE ZONES IS DEPICTED WELL IN
GUIDANCE. SEAS WILL CONSIST OF LIGHT SWELL FROM THE W IN THE PZ5
AND NORTHERN PZ6 ZONES DUE TO AN ACTIVE PATTERN NEAR 140W. FROM
SUN THROUGH TUE, WAVES WILL INCREASE TO 12-13 FT IN N SWELL
ASSOCIATED WITH THE HIGHER WINDS NEAR THE COASTAL TROUGH. THE GFS
WAVE WILL BE USED THROUGH SAT TO MATCH THE WINDS GRIDS, THEN THE
EC WAVE WILL BE USED FOR THE REST OF THE FORECAST.
EXTRATROPICAL STORM SURGE GUIDANCE
N/A
WARNINGS
PRELIMINARY.
PZ5 WASHINGTON/OREGON WATERS
NONE.
PZ6 CALIFORNIA WATERS
NONE.
.FORECASTER ROWLAND/FOLMER. OCEAN PREDICTION CENTER.
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