979  
FXHW52 PHFO 200056  
SRDHFO  
 
COLLABORATIVE NEARSHORE SWELL AND WIND FORECAST FOR OAHU  
NWS/NCEI HONOLULU HI  
256 PM HST WED JUL 19 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 7 ENE 7 3 4 UP 17-21 ENE UP  
07/19 2 S 12 2 4 SAME  
 
THU 8 ENE 7 4 5 UP LOW 19-23 ENE UP  
07/20 2 S 11 2 4 SAME LOW  
 
FRI 8 ENE 8 4 6 UP LOW 17-21 ENE DOWN  
07/21 2 S 11 2 4 SAME LOW  
 
SAT 6 ENE 7 2 4 DOWN LOW 11-16 ENE DOWN  
07/22 6 E 12 6 10 UP LOW  
2 S 11 2 4 SAME LOW  
 
SUN 9 E 11 8 12 UP LOW 11-16 NE DOWN  
07/23 2 S 11 2 4 SAME LOW  
 
MON 9 ENE 11 8 12 DOWN LOW 7-10 NE DOWN  
07/24 2 S 11 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...  
EASTERN EXPOSURES TOPPING THE HEIGHTS.  
 
DETAILED...  
MID WEDNESDAY ON EASTERN SHORES HAS BREAKERS FROM 45-80 DEGREES AT  
LEVELS A NOTCH BELOW AVERAGE. HEIGHTS ARE BUILDING.  
 
SURFACE HIGH PRESSURE NEAR 40N TO THE N TO NNW OF HAWAII HAS  
ESTABLISHED MODERATE TO FRESH TRADES OVER OAHU AND TO THE  
IMMEDIATE E TO NE. THE 7/19 PACIOOS MOKAPU, OAHU BUOY SHOWS A RISE  
IN THE 4-8 SECOND WAVE BAND.  
 
MODELS SUGGEST OVER AND NEARBY WINDS NOSING INTO THE STRONG  
BRACKET ON THURSDAY...THAT SHOULD BRING THE SURF UP TO AVERAGE OR  
HIGHER LEVELS. THE ELEVATED LEVELS SHOULD CONTINUE ON FRIDAY FROM  
45-80 DEGREES.  
 
TROPICAL SYSTEM FERNANDA IS TRACKING MORE INTO THE OAHU SWELL  
WINDOW 7/19. SEE THE LATEST FORECASTS AND DISCUSSIONS OF THE  
NATIONAL HURRICANE CENTER FOR DETAILS ON PROJECTED TRACK AND  
STRENGTH.  
 
THE STRONGEST STAGES OF FERNANDA 7/14-16 HAVE GENERATED SWELL  
THAT IS STARTING TO ARRIVE AT THE PACIOOS HILO, HAWAII BUOY 7/19.  
AS HAS BEEN THE CASE BEFORE...THE WAVE WATCH III BIASED HIGH FOR  
THE ONSET STAGE OF THE LONGEST WAVE PERIOD ENERGY THAT WAS DUE  
7/18. AS THE WAVE INTERVALS SETTLE MORE NEAR MODERATE WAVE  
PERIODS, THE MODEL TENDS TO DO BETTER. THE 12-16 SECOND ENERGY IS  
STEADILY RISING WEDNESDAY MORNING OFF HILO FROM 95-110  
DEGREES...WHICH PLACES OAHU IN THE SHADOW...OTHER THAN LOW SWELL  
FROM REFRACTION AND DIFFRACTION. THE WAVE MODELS SHOW A DECLINE  
IN THE DOMINANT WAVE PERIODS PASSING THROUGH THE HAWAIIAN ISLAND  
CHAIN 7/19-21 THEN HOLDING STEADY AT THE UPPER-END WINDSWELL,  
LOWER-END SWELL BRACKET THROUGH THE WEEKEND INTO MONDAY.  
 
FOR THURSDAY INTO FRIDAY...THE SWELL GENERATED BY FERNANDA  
REACHING OAHU SHOULD BE WELL LESS THAN THE TRADE WINDSWELL  
ENERGY...ESPECIALLY FOR THE SOUTHERN HALF OF THE WINDWARD SIDE  
WITH GREATER SHADOWING.  
 
BASED ON THE 7/19 NHC FORECASTS...THE WEAKENING AND MORE WESTWARD  
TRACKING FERNANDA SHOULD HAVE A ONLY A COMPACT AREA OF WINDS  
STRONGER THAN NEAR GALES. HOWEVER...A BROAD AREA OF STRONG TO NEAR  
GALE BREEZES HAS ALREADY BEEN ESTABLISHED NORTH OF FERNANDA AND IS  
EXPECTED TO HOLD. THE TUESDAY NIGHT 7/18-19 ASCAT SATELLITE SHOWED  
THIS LARGE AREA OF STRONG WINDS TO 27N...WELL ENOUGH NORTH TO AIM  
WINDSWELL AT OAHU. THIS AREA IS ABOUT 1000 NM AWAY. THE DOMINANT  
WAVE PERIOD SHOULD START TO TREND UP LOCALLY FRIDAY INTO  
SATURDAY...BRINGING BREAKERS STEADILY MORE ABOVE AVERAGE FROM  
WITHIN 45-90 DEGREES.  
 
MOST RECENT NHC FORECASTS OF FERNANDA SHOW THE SYSTEM AS A  
TROPICAL DEPRESSION OR REMNANT TO THE NE OF OAHU MONDAY MORNING.  
THIS LOCATION WOULD RESULT IN A DECREASE IN LOCAL WINDS OF MORE  
NORTHERLY COMPONENT SUNDAY INTO MONDAY. SURF FROM FERNANDA SHOULD  
PEAK LOCALLY WITHIN LATE SUNDAY TO LATE MONDAY. STAY TUNED TO THE  
LATEST UPDATES FOR SPECIFICS ON SIZE AND TIMING.  
 
THE ABOVE AVERAGE SURF...HIGH ASTRONOMICAL TIDES...AND ABOVE  
AVERAGE LOCAL MEAN SEA LEVEL SHOULD RESULT IN ABOVE AVERAGE  
COASTAL WAVE WASH DURING THE PM HIGH TIDES FRIDAY INTO MONDAY.  
 
MID WEDNESDAY ON NORTHERN SHORES HAS SMALL BREAKERS FOR EXPOSURES  
TO TRADE WINDSWELL AND FLAT CONDITIONS ELSEWHERE. MORE OF THE SAME  
IS EXPECTED THROUGH THE PERIOD WITH THE TREND AFOREMENTIONED.  
 
MID WEDNESDAY ON SOUTHERN SHORES HAS BREAKERS BELOW THE SUMMER  
AVERAGE FROM WITHIN 140-190 DEGREES. SIMILAR CONDITIONS ARE  
EXPECTED ON THURSDAY. EASTERLY EXPOSURES OF THE SOUTH SHORE SHOULD  
TREND AS AFOREMENTIONED.  
 
A LARGE AREA OF SURFACE LOW PRESSURE IN THE SOUTHERN HEMISPHERE  
MID LATITUDES SOUTH OF FRENCH POLYNESIA STRETCHING NW TO NE OF NEW  
ZEALAND WAS MOSTLY SUB-GALE IN STRENGTH. IT WAS SLOW MOVING WITH A  
GRADUAL EASTWARD SHIFT 7/12-16. IT WILL LIKELY BE THE SOURCE OF  
THE SUMMER BACKGROUND CONDITIONS AS FOUND 7/19 CONTINUING THROUGH  
THE PERIOD.  
 
INTO THE LONG RANGE...DORMANT CONDITIONS E TO SE OF NEW ZEALAND  
SHOULD KEEP SURF FROM 160-200 DEGREES AT A MINIMUM 7/25-28. MODELS  
SHOW GALES NOSING INTO THE SUBTROPICS 7/20-21 IN THE TASMAN SEA.  
THIS COULD BRING THE NEXT LONGER PERIOD SWELL ABOVE BACKGROUND  
LEVEL WITHIN 7/27-29 FROM 208-220 DEGREES.  
 
IN THE TROPICAL EASTERN NORTH PACIFIC...TROPICAL CYCLONE GREG HAS  
FORMED AND COULD BRING EASTERLY EXPOSURES A HANA HOU TO THE  
FERNANDA GIG MID TO LATE NEXT WEEK. IT IS TOO EARLY FOR  
SPECIFICS.  
 
LONG RANGE FORECASTS ARE SUBJECT TO LOW CONFIDENCE.  
 
THIS COLLABORATIVE FORECAST WILL RESUME ON FRIDAY...JULY 21.  
 
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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