586  
FXHW52 PHFO 010041  
SRDHFO  
 
COLLABORATIVE NEARSHORE SWELL AND WIND FORECAST FOR OAHU  
NWS/NCEI HONOLULU HI  
241 PM HST FRI JUL 31 2020  
 
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 6 ENE 7 3 5 DOWN 13-19 ENE DOWN  
07/31 2 SSW 14 3 5 UP  
2 SE 10 2 3 UP  
 
SAT 5 E 7 2 4 DOWN LOW 12-18 E DOWN  
08/01 2 S 12 2 4 DOWN LOW  
2 SE 10 2 3 SAME LOW  
1 NNE 13 1 3 UP LOW  
 
SUN 5 E 6 1 3 SAME LOW 12-18 E SAME  
08/02 2 SE 10 2 3 SAME LOW  
2 NNE 11 2 4 UP LOW  
 
MON 5 E 6 1 3 SAME LOW 12-18 E SAME  
08/03 2 SE 10 2 3 SAME LOW  
2 NNE 9 1 3 DOWN LOW  
 
TUE 6 E 6 2 3 UP LOW 13-19 E UP  
08/04 2 SE 10 2 3 SAME LOW  
1 SSW 17 2 4 UP LOW  
 
WED 6 E 7 3 5 UP LOW 17-21 E UP  
08/05 2 SE 9 1 3 DOWN LOW  
2 S 15 3 5 UP 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-END SUMMER SURF.  
 
DETAILED...  
MID FRIDAY ON EASTERN SHORES HAS BREAKERS FROM 60-90 DEGREES NEAR THE  
TRADE WIND SWELL AVERAGE. HEIGHTS ARE PREDICTED TO DROP A NOTCH ON  
SATURDAY.  
 
THE CENTER OF A BROAD AREA OF SURFACE HIGH PRESSURE TO 1029 MB 7/31  
IS LOCATED JUST EAST OF THE DATE LINE NEAR 35N WITH A RIDGE AXIS  
EXTENDED EASTWARD TO THE N OF HAWAII. A BROAD UPPER LEVEL TROUGH  
EXTENDING SSW DOWN FROM THE GULF OF ALASKA TO NE OF HAWAII 7/31 HAS  
WEAKENED THE SURFACE PRESSURE TO THE E TO NE OF HAWAII. IN TURN,  
TRADES UPSTREAM OF HAWAII AS VALIDATED BY THE ASCAT SATELLITE 7/31  
HAVE DROPPED WITHIN GENTLE TO MODERATE FOR MOST OF THE AREA OUT TO  
THE ENE TO NE, WHILE MODERATE TRADES WITH SMALL POCKETS TO FRESH  
CONTINUE FRIDAY MORNING TO THE DUE E OF OAHU. THIS PATTERN IS  
EXPECTED TO HOLD INTO EARLY NEXT WEEK. THIS SHOULD BRING BREAKERS  
FROM WIND SWELL BELOW AVERAGE BY SATURDAY AND HOLDING LOW INTO NEXT  
WEEK FROM 70-90 DEGREES.  
 
MODELS SHOW SURFACE HIGH PRESSURE INCREASING NORTH OF THE STATE  
8/4-5, THAT SHOULD TREND UP LOCAL TRADES AND WIND SWELL SURF FROM  
70-90 DEGREES.  
 
MID FRIDAY ON NORTHERN SHORES HAS BREAKERS FOR SELECT EXPOSURES TO  
TRADE WIND SWELL. HEIGHTS SHOULD TREND AFOREMENTIONED.  
 
AN OCCLUDED LOW PRESSURE SYSTEM IN THE NE PACIFIC UNFOLDED 7/28. THE  
NEARLY STATIONARY, COMPACT SYSTEM HAD A RIBBON OF NEAR GALE BREEZES  
AIMED AT HAWAII OVER THE 010-020 DEGREE BAND WITH THE HEAD OF THE  
FETCH ABOUT 1600 NM AWAY 7/28-29. THE SURFACE WINDS WEAKENED TO  
SUB-GALE BY 7/30. SMALL BREAKERS ARE EXPECTED TO PICK UP LOCALLY  
LATE SATURDAY, PEAK ON SUNDAY, THEN DROP ON MONDAY CENTERED FROM 015  
DEGREES.  
 
MID FRIDAY ON SOUTHERN SHORES HAS AN INCREASE IN SURF NOSING TOWARDS  
THE AVERAGE ON THE LESS FREQUENT, THOUGH COMMON SETS. THIS  
SHORT-LIVED EVENT IS EXPECTED TO TREND DOWN SATURDAY.  
 
A BROAD AREA OF LOW PRESSURE SET UP E TO SE OF NEW ZEALAND 7/22-24.  
IT AIMED MOSTLY AT THE AMERICAS, EXCEPT FOR A SHORT-LIVED FETCH  
CENTERED ON 190 DEGREES WITHIN 45-55S, 170W 7/23.  
 
SOUTHERN NOAA AND PACIOOS/CDIP BUOYS SHOW AN UPWARD TICK IN THE 14-16  
SECOND BAND FRIDAY MORNING 7/31 FROM 180-195 DEGREES. THE EVENT WILL  
LIKELY PEAK LATE FRIDAY 7/31 AND DROP SATURDAY FROM THE SAME  
DIRECTION.  
 
SOUTHERN HEMISPHERE AND EQUATORIAL TRADES WITHIN FRESH TO STRONG  
LEVELS COVERED A LARGE AREA WITHIN 120-150W OVER 20S TO 7N.  
PACIOOS/CDIP SOUTHERN BUOYS SHOW A RISE IN THE 8-10 SECOND BAND 7/31.  
THIS LOW ENERGY, SHORTER-PERIOD SWELL FROM 140-160 DEGREES IS MAKING  
FOR SMALL BREAKERS FOR EXPOSURES TO THE SE. MODELS SUGGEST THE EVENT  
TO BE LONG-LIVED.  
 
AN EAST-MOVING GALE LOW S OF NEW ZEALAND 7/27 BEGAN AN EQUATORWARD  
TRACK NEAR 160W 7/28. THE OCEAN SURFACE WINDS WEAKENED TO MOSTLY NEAR  
GALES AS THE FETCH STRETCHED TOWARD THE SUBTROPICS. ASCAT 7/29 AM  
SHOWED THE HEAD OF THE FETCH TO 35S. THE FETCH TOWARDS HAWAII MOSTLY  
ENDED 7/30 AS THE SEAS WERE AIMED TOWARD THE NW WELL SW OF HAWAII.  
 
THE INITIAL STAGE COULD BRING LOW, INCONSISTENT, LONG-PERIOD SURF  
LOCALLY 8/4 FROM 190-200 DEGREES. BETTER ODDS FOR THE MODERATE WAVE  
PERIOD STAGE WITH SURF BUILDING FROM 170-190 DEGREES TO NEAR AVERAGE  
8/5.  
 
INTO THE LONG RANGE, THE TEMPERATE SOUTH SWELL EVENT SHOULD PEAK 8/6  
THEN DROP TO BACKGROUND BY 8/7. IN GENERAL, THE FIRST TWO WEEKS OF  
AUGUST ARE NOT LOOKING MUCH DIFFERENT THAN THE LAST 3 WEEKS OF JULY  
WITH MOSTLY SEASONALLY MINIMAL SURF AND SHORT-LIVED PEAK DAYS TO NEAR  
AVERAGE. HINTS OF AN UPTICK IN THE THIRD WEEK OF AUGUST FROM THE NEW  
ZEALAND SOURCE.  
 
EAST SIDE SHOULD HAVE NEAR AVERAGE BREAKERS FROM TRADE WIND OUT OF  
60-90 DEGREES 8/6-8.  
 
LONG RANGE FORECASTS ARE SUBJECT TO MAJOR REVISIONS.  
 
THE NEXT COLLABORATIVE FORECAST WILL BE UPDATED MONDAY, AUGUST 3.  
 
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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