929  
FXHW52 PHFO 280123  
SRDHFO  
 
COLLABORATIVE NEARSHORE SWELL AND WIND FORECAST FOR OAHU  
NWS/NCEI HONOLULU HI  
323 PM HST MON MAR 27 2017  
 
THIS COLLABORATIVE FORECAST WILL BE UPDATED MONDAY THROUGH FRIDAY AT  
300 PM WHEN PAT CALDWELL IS AVAILABLE/  
 
FORECAST SWL DMNT DMNT H H HGT WIND WIND SPD  
DATE HGT DIR PD 1/3 1/10 TEND PROB SPD DIR TEND  
 
1 PM 8 WNW 14 14 18 DOWN 11-16 E DOWN  
03/27 6 E 8 3 4 SAME  
 
TUE 7 NW 14 12 16 DOWN LOW 11-16 E SAME  
03/28 5 E 8 3 4 SAME LOW  
 
WED 8 NW 14 14 18 UP LOW 11-16 E SAME  
03/29 5 E 8 3 4 SAME LOW  
 
THU 7 NNW 13 12 14 DOWN LOW 11-16 E SAME  
03/30 5 E 8 3 4 SAME LOW  
2 SSW 16 2 4 UP LOW  
 
FRI 12 WNW 18 28 34 UP LOW 11-16 E SAME  
03/31 5 E 8 3 4 SAME LOW  
2 SSW 16 2 4 SAME LOW  
 
SAT 10 NW 15 20 26 DOWN LOW 17-21 E UP  
04/01 7 E 7 3 5 UP LOW  
2 SSW 15 2 4 SAME LOW  
 
LEGEND:  
SWL HGT OPEN OCEAN SWELL HEIGHT MEASURED FROM TROUGH TO CREST  
IN FEET LOCATED 20 NAUTICAL MILES OFFSHORE  
DMNT DIR DOMINANT DIRECTION TYPICALLY +/-10 DEGREES IN 16 COMPASS  
POINTS  
DMNT PD DOMINANT PERIOD IN SECONDS  
H1/3 SIGNIFICANT WAVE HEIGHT IN THE SURF ZONE  
H1/10 AVERAGE HEIGHT OF THE HIGHEST ONE-TENTH WAVES IN THE SURF  
ZONE  
HGT TEND HEIGHT TENDENCY OF SWELL (VALID VALUES: UP/DOWN/SAME)  
PROB PROBABILITY OF OCCURRENCE (VALID VALUES: HIGH/MED/LOW)  
WIND SPD OPEN WATER WIND SPEED MEASURED IN KNOTS LOCATED  
20 NAUTICAL MILES OFFSHORE  
WIND DIR WIND DIRECTION IN 16 COMPASS POINTS  
SPD TEND WIND SPEED TENDENCY (VALID VALUES: UP/DOWN/SAME)  
 
SURF HEIGHTS WILL VARY BETWEEN DIFFERENT BEACHES AND AT THE SAME  
BEACH AT DIFFERENT BREAK AREAS.  
 
DISCUSSION:  
SUMMARY...  
WINTRY SURF CONTINUES.  
 
DETAILED...  
MID MONDAY ON NORTHERN SHORES HAS BREAKERS ABOVE THE MARCH AVERAGE  
FROM 280-325 DEGREES...CENTERED NEAR 310 DEGREES. HEIGHTS ARE  
EXPECTED TO TREND DOWN THOUGH REMAIN ABOVE AVERAGE ON TUESDAY FROM  
THE SAME DIRECTION.  
 
THE JET STREAM HOLDS IN WINTER MODE WITH A MORE SOUTHERLY TRACK  
THAN EXPECTED IN SPRING AND AN ALEUTIAN LOW FAVORING LONGITUDES  
NEAR THE DATELINE. SUCH PATTERNS KEEP SURF IN HAWAII ABOVE  
AVERAGE.  
 
A HURRICANE-FORCE LOW PRESSURE SYSTEM FORMED OFF JAPAN 3/21 AND  
ANCHORED NEAR THE DATELINE BY 3/23. THIS SYSTEM GAVE THE EXTRA-  
LARGE SURF FROM 280-320 DEGREES THAT GREW RAPIDLY 3/25 AND PEAKED  
ON 3/26.  
 
THE NW HAWAII NOAA BUOYS 3/27 IN THE MORNING SHOW A STEADY  
DOWNWARD TREND FOR THE LONG-PERIOD ENERGY IN THE 16-19 SECOND  
BAND. THE MODERATE PERIODS OF 13-15 SECONDS ARE HOLDING STEADY.  
 
THIS EVENT IS EXPECTED TO SLOWLY DECLINE TUESDAY FROM 280-325  
DEGREES WITH A NEW EVENT DUE LATE TUESDAY.  
 
A LONG-LIVED AREA OF SURFACE LOW PRESSURE NEAR THE DATELINE WITHIN  
30-55N LATITUDE THAT SET UP 3/23 HAD A REINFORCEMENT LOW MERGE  
FROM THE SW IN ON 3/25. A LONG...WIDE FETCH OF GALES OVER THE  
305-325 DEGREE BAND OVERTOOK EXISTING SEAS...WHICH MAINTAINED WAVE  
HEIGHTS ABOVE 20 FEET. THE HEAD OF THE FETCH WAS ABOUT 1400 NM  
AWAY 3/26. THE SYSTEM NOSED TO WITHIN 1200 NM 3/27 AS THE WINDS  
DECREASED AND THE LOW CENTER SHIFTED NORTH.  
 
THE WINDS WERE NOT AS EXTREME AS THE PREVIOUS SYSTEM...SO THE  
DOMINANT WAVE PERIODS ARE EXPECTED TO BE SHORT-LIVED IN THE 16-17  
SECOND BAND...BUT SETTLE SOON TO THE 13-15 SECOND BAND AND HOLD  
STEADY. THE LONGEST WAVE PERIOD ARE DUE TUESDAY NEAR SUNDOWN  
LOCALLY FROM 305-320 DEGREES. SURF SHOULD PEAK ABOVE AVERAGE ON  
WEDNESDAY FROM 305-325 DEGREES. IT SHOULD REMAIN ABOVE AVERAGE  
THURSDAY AS IT SLOWLY DECLINES. A NEW EVENT IS DUE THURSDAY  
EVENING.  
 
A REPEAT PATTERN OF THE JAPAN-TO-DATELINE...EXTRATROPICAL-CYCLONE  
EXPRESS IS EXPECTED 3/27-29 TO BRING A SIMILAR ROUND OF EXTRA-  
LARGE...OR SURF HIGH ENOUGH FOR OUTER REEFS...LATER IN THE WEEK.  
 
THE LOW HAS FORMED EAST OF JAPAN. AT 12Z...2017-03-27...THE CENTER  
OF 979 MB IS NEAR 35N...150E OR ABOUT 2900 NM WNW OF HAWAII. THE  
SYSTEM IS GAINING HURRICANE FORCE. IT IS MODELLED TO TRACK  
ENE...REACHING THE DATELINE 3/29.  
 
AS WITH THE EVENT OF 3/25-27...THE FIRST 48 HOURS HAS STRONGEST  
WINDS OVER THE 280-305 DEGREE BAND RELATIVE TO HAWAII. THE HEAD OF  
THE FETCH IS PREDICTED TO REACH ABOUT 1200 NM AWAY BY EARLY 3/29.  
LONG-PERIOD FORERUNNERS ARE DUE LOCALLY NEAR SUNDOWN  
THURSDAY...WITH A STEADY RISE OVERNIGHT. THIS MORE WESTERLY  
COMPONENT SWELL SHOULD PEAK FRIDAY 3/31 BUT HOLD INTO SUNDAY 4/2.  
 
DIFFERENT FROM THE PREVIOUS EVENT...THIS NEW SYSTEM IS MODELLED  
TO TRACK FURTHER EAST OF THE DATELINE...THUS CLOSER AND  
BIGGER...AS IT ADDS WAVE ENERGY TO THE 305-330 DEGREE BAND  
3/29-30. THE HEAD OF THE FETCH OF GALES IS PREDICTED WITHIN 1000  
NM BY LATE 3/29. THE FETCH OVER THIS AREA IS EXPECTED TO BE LONG-  
LIVED...WITH ADDITIONAL ENERGY ADDED FROM 330-360 DEGREES AS THE  
SYSTEM WEAKENS NEAR THE EASTERN ALEUTIANS 3/30-31.  
 
PROXIMITY TO THE HIGH SEAS EAST OF THE DATELINE SHOULD MAKE THIS  
EVENT LARGER THAN THE EVENT LOCALLY OF 3/25-27. DOMINANT ENERGY  
CENTERED NEAR 310 DEGREES SHOULD BE FILLED IN BY FRIDAY 3/31. THE  
DIRECTIONAL BAND SHOULD BE WIDE...FROM 280-330 DEGREES. EXTRA-  
LARGE SURF SHOULD HOLD FRIDAY INTO SATURDAY AS THE EVENT SLOWLY  
DECLINES.  
 
MID MONDAY ON EASTERN SHORES HAS BREAKERS FROM 70-100 DEGREES A  
NOTCH BELOW THE TRADE WINDSWELL AVERAGE. SIMILAR SURF IS PREDICTED  
FOR TUESDAY.  
 
SEE THE LATEST NWS STATE FORECAST DISCUSSION FOR AN EXPLANATION OF  
THE LOCAL TREND IN TRADES.  
 
SURFACE HIGH PRESSURE BETWEEN HAWAII AND CALIFORNIA HAS STRONGEST  
TRADES WELL EAST OF HAWAII NEAR 21N OR SOUTHWARD. THIS UPSTREAM  
SOURCE SHOULD KEEP LOW TO MODERATE WINDSWELL OF 7-10 SECONDS  
LOCALLY THROUGH THE WEEK. THE LONGER WAVE PERIODS SHOULD KEEP SURF  
ABOUT THE SAME THROUGH THE WEEK FROM 70-100 DEGREES. THE LOCAL  
WINDS ARE EXPECTED NEAR THE MODERATE BRACKET...WHICH WOULD NOT BE  
SUFFICIENT TO KEEP SUCH SURF WITHOUT THE REMOTE SOURCE.  
 
BREAKERS FROM WINDSWELL OUT OF 70-90 DEGREES IS PREDICTED TO  
INCREASE OVER THE WEEKEND.  
 
MID MONDAY ON SOUTHERN SHORES HAS LOW ENERGY FROM SWELL OUT OF THE  
SOUTHERN HEMISPHERE...AND LARGER BREAKERS FOR EXPOSURES TO THE  
NORTH PACIFIC...MORE WESTERLY COMPONENT SWELL. THE LATTER IS  
EXPECTED TO DECLINE ON TUESDAY.  
 
A SERIES OF LOW PRESSURES TRACKED SE OF NEW ZEALAND 3/20-27. THE  
EARLIER ONES HAD NEW LOW PRESSURES FOLLOWING TOO CLOSELY SO THE  
AIM OF HIGH SEAS WAS MORE ZONAL...OR WEST TO EAST. ANGULAR  
SPREADING SHOULD ALLOW LOW...LONG-PERIOD SWELL LOCALLY LESS THAN 2  
FEET 3/27-29 FROM 180-220 DEGREES.  
 
STRONGER LOWS WITH A FOLLOWING HIGH PRESSURE TO ALLOW MORE AIM  
TOWARDS HAWAII OCCURRED 3/23-25. SEAS BARELY TOPPED 20  
FEET...THOUGH THE FETCH AREA WAS WIDE. IT SHOULD AT LEAST ALLOW  
THE LOCAL SURF TO CLIMB TO SUMMER BACKGROUND LEVELS STARTING 3/30  
FROM 180-200 DEGREES.  
 
INTO THE LONG RANGE...SIMILAR SURF INTO THE WEEKEND FROM 180-200  
DEGREES IS LIKELY. A STRONGER SYSTEM BUT FURTHER AWAY TO THE SE OF  
NEW ZEALAND 3/26-27 TRACKED RAPIDLY EAST. IT COULD KEEP A  
BACKGROUND SUMMER SURF PATTERN LOCALLY 4/3-4 FROM 180-200 DEGREES.  
 
IN THE NORTH PACIFIC...SURF SHOULD REMAIN ABOVE AVERAGE INTO 4/2  
WITH A DOWNWARD TREND BELOW AVERAGE BY 4/3 FROM 315-360 DEGREES.  
MODELS SHOW A COMPACT GALE FORMING NEAR THE DATELINE 4/1 WITH A NE  
TRACK. IT COULD MAKE A NNW EVENT NEAR AVERAGE ROUGHLY 4/4-5. HINTS  
OF A LARGER NW EVENT A FEW DAYS LATER...4/7-8.  
 
BREAKERS FROM TRADE WINDSWELL ARE EXPECTED TO REACH THE AVERAGE BY  
4/2 AND HOLD INTO 4/3 OUT OF 70-90 DEGREES.  
 
LONG RANGE FORECASTS ARE SUBJECT TO LOW CONFIDENCE.  
 
THIS COLLABORATIVE FORECAST WILL RESUME ON WEDNESDAY...MARCH 29.  
 
THIS FORECAST WAS PRODUCED THROUGH THE COLLABORATIVE EFFORTS OF  
NWS AND NCEI. PLEASE SEND SUGGESTIONS TO W-HFO.WEBMASTER@NOAA.GOV  
OR CALL THE WARNING COORDINATION METEOROLOGIST AT 808-973-5275.  
 
ADDITIONAL RESOURCES:  
SEE /IN LOWERCASE/ HTTP://WWW.PRH.NOAA.GOV/HNL/PAGES/MARINE.PHP  
 

 
 
NWS FORECASTER AND NCEI PAT CALDWELL  
 
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