534  
FXHW52 PHFO 200039  
SRDHFO  
 
COLLABORATIVE NEARSHORE SWELL AND WIND FORECAST FOR OAHU  
NWS/NCEI HONOLULU HI  
239 PM HST FRI APR 19 2019  
 
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 4 NNW 13 6 8 UP 13-19 E UP  
04/19 7 E 6 2 4 UP  
 
SAT 3 NNW 11 4 6 DOWN MED 17-21 E SAME  
04/20 7 E 7 3 4 UP LOW  
 
SUN 2 NNW 10 1 3 DOWN LOW 13-19 E DOWN  
04/21 7 E 7 3 4 DOWN LOW  
 
MON 2 NNW 10 1 3 SAME LOW 13-16 E SAME  
04/22 6 E 7 2 4 SAME LOW  
2 S 16 3 5 UP LOW  
 
TUE 2 NW 10 1 3 SAME LOW 13-19 E SAME  
04/23 6 E 7 2 4 SAME LOW  
2 S 15 3 5 SAME LOW  
 
WED 2 NNW 10 1 3 SAME LOW 13-19 E SAME  
04/24 6 E 7 2 4 SAME LOW  
2 S 14 3 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 IN 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... LOW SPRING MODE.  
 
DETAILED...  
MID FRIDAY ON NORTHERN SHORES HAS BREAKERS FROM 325-345 DEGREES AT  
LEVELS A NOTCH BELOW THE APRIL AVERAGE. HEIGHTS ARE PREDICTED TO  
TREND DOWN LATE FRIDAY INTO SATURDAY.  
 
A WIDE, LONG FETCH OF STRONG TO NEAR GALE BREEZES FOLLOWED A SE-  
PUSHING FRONT FROM NEAR THE DATE LINE ON THE ALEUTIANS SUNDAY 4/14  
TO ABOUT 1000 NM AWAY FROM HAWAII LATE 2/16. THE SYSTEM MOVED EAST  
OF THE HAWAII SWELL WINDOW WEDNESDAY 4/17.  
 
NOAA NW HAWAII BUOYS 51001 AND 51101 SHOWED A SHARP RISE TO A  
MAXIMUM IN THE 12-14 SECOND BAND THURSDAY EVENING 4/18. THE WAVE  
ENERGY HAS BEEN TRENDING DOWN TOWARDS NOON 4/19. THE PACIOOS/CDIP  
HANALEI, KAUAI BUOY REACHED 6 FEET DEEP WATER SWELL FRIDAY  
MORNING THOUGH PEAK HEIGHTS AT THE WAIMEA, OAHU BUOY HAVE BEEN  
LOWER WITHIN 3-4 FEET 4/19 AM. WITH THE LARGE GENERATION AREA,  
THE EVENT SHOULD LINGER AT SMALL LEVELS SATURDAY FROM 325-345  
DEGREES THEN DROP TO TINY TO SMALL LEVELS BY SUNDAY.  
 
A WEAK, ZONAL JET STREAM WITHIN 30-45N ACROSS THE CENTRAL NORTH  
PACIFIC BECAME ESTABLISHED 4/17. A WEAK LOW PRESSURE NEAR 40N,  
170W 4/18-19 COULD KEEP TINY TO SMALL NNW BREAKERS ON MONDAY 4/22.  
ANOTHER WEAK LOW PRESSURE AREA WEST OF THE DATE LINE NEAR 35N,  
170E 4/18-19 IS TRACKING NE. IT SHOULD KEEP A TINY TO SMALL WNW TO  
NNW EVENT LOCALLY 4/23-24.  
 
MID FRIDAY ON EASTERN SHORES HAS BREAKERS FROM 70-90 DEGREES AT  
LEVELS BELOW THE TRADE WINDSWELL AVERAGE. HEIGHTS ARE EXPECTED TO  
RISE SLIGHTLY ON SATURDAY.  
 
THE FETCH OF TRADES AIMED AT HAWAII STRETCHES WELL TO THE EAST OF  
THE ISLANDS BEYOND 1000 NM WITH STRONG BREEZES SOUTH THE LATITUDES  
OF THE ISLANDS, FRESH BREEZES ALONG THE ZONAL BAND WITHIN THE  
ISLANDS, AND GENTLE TO MODERATE BREEZES JUST NORTH OF THE LATITUDE  
OF THE ISLANDS. THIS IS NARROWING THE FETCH AIMED AT OAHU FOR THE  
FRESH BREEZES NECESSARY FOR MAKING WINDSWELL. WIND MODELS SUGGEST  
A SLIGHT MAXIMUM TO THE TRADES ON OAHU FOR SATURDAY 4/20 THAT  
SHOULD COINCIDE WITH A NOTCH MORE SIZE IN THE BREAKERS. HEIGHTS  
SHOULD HOLD NEAR TO BELOW AVERAGE 4/21-23 FROM 70-90 DEGREES.  
 
MID FRIDAY ON SOUTHERN SHORES HAS WAVE ENERGY FROM THE SOUTHERN  
HEMISPHERE AT A MINIMUM. LOW CONDITIONS ARE EXPECTED TO CONTINUE  
ON SATURDAY.  
 
WEAK LOW PRESSURE SYSTEMS S TO SE AND E OF NEW ZEALAND 4/11-13 DID  
NOT HAVE SUFFICIENT STRENGTH TO SEND SURF BEYOND BACKGROUND TO  
HAWAII. WAVE WATCH III DOES SHOW THE DOMINANT BACKGROUND SWELL  
DIRECTION TURNING INTO THE NEW ZEALAND WINDOW NEAR 190 DEGREES BY  
SATURDAY 4/20 INTO 4/21.  
 
BETTER ODDS FOR SURF BUILDING MONDAY. THE JET STREAM FORMED A  
LARGE MERIDIONAL, OR NORTH TO SOUTH, LOOP EAST OF NEW ZEALAND  
4/14-17. AT THE SURFACE, LOW PRESSURE AREAS FILLED 35-70S SOUTH OF  
FRENCH POLYNESIA WHILE HIGH PRESSURE SET UP OVER NEW ZEALAND. THIS  
LONG, WIDE FETCH HAD DIRECT AIM AT HAWAII OVER THE 175-185 DEGREE  
BAND. THE LIMITING FACTOR WAS THE WIND MAGNITUDE, WHICH WAS MOSTLY  
STRONG TO NEAR GALE WINDS WITH POCKETS TO MARGINAL GALES.  
 
THE PACIOOS/CDIP AMERICAN SAMOA BUOY PICKED UP THE NEW SWELL  
4/18-19 WITH DEEP WATER SWELL 6-7 FEET WITH 12-16 SECOND ENERGY.  
SINCE THIS IS AT THE SHORT END OF THE SWELL SPECTRUM, AND SHORTER  
WAVE PERIOD ENERGY LOSES HEIGHT MORE RAPIDLY WITH TRAVEL DISTANCE  
DUE TO GREATER ANGULAR SPREADING, THE POTENTIAL FOR SURF IN HAWAII IS  
LOWER. A SIMILAR READING AT SAMOA WITH 16-20 SECOND ENERGY WOULD  
MEAN A SIGNIFICANT, ABOVE AVERAGE EVENT IN HAWAII.  
 
THE EVENT IS PREDICTED TO FILL IN MONDAY 4/22 TO LEVELS NEAR THE  
SEASONAL AVERAGE. IT SHOULD HOLD ABOUT THE SAME ON TUESDAY WITH A  
DOWNWARD TREND WEDNESDAY.  
 
INTO THE LONG RANGE, THERE WAS A SECOND FETCH AREA OF NEAR GALES  
4/17-18 THAT SHOULD KEEP SURF AT UPPER-END BACKGROUND LEVELS  
LOCALLY THURSDAY 4/24 INTO 4/25. THE OVERALL LONG-WAVE TROUGH  
PATTERN SHIFTED EAST SOUTH OF FRENCH POLYNESIA 4/17-19 WITH  
SOURCES BETTER AIMED AT THE AMERICAS. ANGULAR SPREADING SHOULD  
KEEP UPPER-END BACKGROUND SURF ROLLING INTO THE WEEKEND OF 4/27  
LOCALLY OUT OF 170-180 DEGREES.  
 
ON THE NORTH SHORE, SURF SHOULD REMAIN AT A SEASONAL MINIMUM  
4/24-25. EAST SIDE SHOULD HOVER ABOUT THE SAME A NOTCH BELOW THE  
AVERAGE.  
 
LONG RANGE FORECASTS ARE SUBJECT TO HIGH UNCERTAINTY.  
 
THIS COLLABORATIVE FORECAST WILL RESUME ON MONDAY, APRIL 22.  
 
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 HTTPS://WWW.WEATHER.GOV/HFO/MARINE  
 

 
 
NWS FORECASTER AND NCEI PAT CALDWELL  
 
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