438  
FXHW52 PHFO 220057  
SRDHFO  
 
COLLABORATIVE NEARSHORE SWELL AND WIND FORECAST FOR OAHU  
NWS/NCEI HONOLULU HI  
257 PM HST FRI SEP 21 2018  
 
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 E 9 3 5 DOWN 11-16 E SAME  
09/21 2 S 12 2 4 SAME  
 
SAT 2 N 10 2 4 UP LOW 11-16 E SAME  
09/22 5 E 8 2 4 DOWN LOW  
2 S 11 2 3 DOWN LOW  
 
SUN 2 N 10 2 4 SAME LOW 9-13 ESE DOWN  
09/23 4 E 8 2 3 DOWN LOW  
2 S 11 2 3 SAME LOW  
 
MON 2 NNE 9 2 3 DOWN LOW 7-10 SSE SAME  
09/24 2 SSE 11 2 3 SAME LOW  
 
TUE 2 SSE 11 2 3 SAME LOW 9-13 S UP  
09/25  
 
WED 2 SSE 11 2 3 SAME LOW 9-13 S SAME  
09/26  
 
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 SPELL.  
 
DETAILED...  
MID FRIDAY ON EASTERN SHORES HAS BREAKERS FROM 60-100 DEGREES AT  
LEVELS NEAR THE TRADE WINDSWELL AVERAGE. HEIGHTS ARE EXPECTED TO  
FALL ON SATURDAY.  
 
SEE THE LATEST NWS STATE FORECAST DISCUSSION REGARDING THE LOCAL  
WEATHER AND WINDS AS WE ENTER THE FIRST WEEK OF FALL.  
 
ENHANCED TRADES ON THE EAST SIDE OF THE REMNANT PAUL INVERTED  
TROUGH 9/16-20 WAS THE SOURCE FOR THE E WINDSWELL THAT FILLED IN  
LOCALLY ABOVE AVERAGE 9/19. ASCAT SHOWED WINDS HAVE WEAKENED TO  
MODERATE LEVELS EAST OF HAWAII 9/20-21. WINDS SHOULD FALL TOWARD  
GENTLE IN THE TRADE WIND SOURCE WINDOW SATURDAY INTO NEXT WEEK  
EAST OF 150W. PACIOOS/CDIP MOKAPU BUOY 9/21 SHOWS A DOWNWARD TREND  
IN THE 8-10 SECOND WAVE PERIOD ENERGY. THIS EVENT SHOULD DROP  
BELOW AVERAGE ON SATURDAY AND CONTINUE TO FALL TO AN EAST SIDE  
MINIMUM BY LATE SUNDAY.  
 
MID FRIDAY ON NORTHERN SHORES HAS NEAR NIL SURF. THE PACIOOS/CDIP  
HANALEI, KAUAI AND WAIMEA, OAHU BUOYS SHOW A PINCH OF W SWELL  
ENERGY GENERATED BY A TYPHOON NEAR THE PHILIPPINES LAST WEEK. A  
NEW SHORT-PERIOD EVENT IS DUE ON SATURDAY.  
 
FRESH TO STRONG BREEZES WITH SMALL POCKETS TO NEAR GALE SET UP  
BETWEEN A HIGH PRESSURE AT 50N, 170W AND LOWER PRESSURE TO ITS SE  
9/19-21. THE PATTERN SHIFTED EASTWARD AND IS EXPECTED TO EXIT THE  
HAWAII SWELL WINDOW BY 9/22.  
 
TINY TO SMALL BREAKERS FROM REMOTE WINDSWELL ARE MODELLED TO PICK  
UP LOCALLY FROM 340-360 DEGREES SATURDAY PM. IT SHOULD HOLD ABOUT  
THE SAME SUNDAY THEN FALL ON MONDAY AS THE DIRECTION VEERS ON THE  
COMPASS MORE TO 000-020 DEGREES BY MONDAY.  
 
MID FRIDAY ON SOUTHERN SHORES HAS BACKGROUND SURF. SIMILAR BELOW  
AVERAGE CONDITIONS ARE ON TAP FOR SATURDAY.  
 
TRADES FROM THE SOUTHERN HEMISPHERE SHOULD KEEP LOW, SHORTER-  
PERIOD BREAKERS FROM 140-180 DEGREES THROUGH THE PERIOD WITH A  
SLIGHT BACKING ON THE COMPASS WHILE LOW, LONGER-PERIOD SWELL FROM  
180-220 DEGREES OVERLAPS. THE LATTER ARE FROM MID LATITUDE EXTRA-  
TROPICAL CYCLONES SOUTH OF 50S TO THE SW TO SE OF NEW ZEALAND  
9/14-19 THAT AIMED SEAS MOSTLY WEST TO EAST.  
 
INTO THE LONG RANGE, SEAS ABOVE 40 FEET FOR A SYSTEM SW OF NEW  
ZEALAND AND S TO SE OF TASMANIA 9/20-21 WEAKENED AS IT MOVED  
EAST. MODELS BRING IN SLIGHTLY HIGHER SWELL LOCALLY FRIDAY 9/28  
WITH SURF FROM 208-220 DEGREES POTENTIALLY NOSING TOWARD THE  
SUMMER AVERAGE INTO 9/29.  
 
MODELS SHOW LOW PRESSURE TO THE NNW OF HAWAII 9/24-27 THAT COULD  
BRING SURF TO THE NORTH SHORE SEPTEMBER AVERAGE OR HIGHER FROM  
NNW TO N 9/28-30.  
 
EAST SIDE IS EXPECTED TO REMAIN AT A MINIMUM 9/27-28.  
 
LONG RANGE FORECASTS ARE SUBJECT TO HIGH UNCERTAINTY.  
 
THIS COLLABORATIVE FORECAST WILL RESUME ON MONDAY, SEPTEMBER 24.  
 
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 HTTP://WWW.PRH.NOAA.GOV/HNL/PAGES/MARINE.PHP  
 

 
 
NWS FORECASTER AND NCEI PAT CALDWELL  
 
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