961  
FXHW01 KWNH 201211  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
810 AM EDT FRI OCT 20 2017  
 
VALID 00Z SAT OCT 21 2017 - 00Z SAT OCT 28 2017  
   
..HEAVY RAIN THREAT FOR NEXT WEEK
 
 
BREEZY TRADES WILL SLOWLY SUBSIDE OVER THE NEXT FEW DAYS WITH  
GENERALLY LIGHT WINDWARD/MAUKA SHOWERS EXPECTED. NEXT WEEK, A  
TROUGH IS FORECAST TO DIG ALONG/PAST 165W NORTH OF 35N (MON 12Z)  
AND LIKELY FORM A CLOSED LOW NEAR 30N/160W PER THE LATEST  
DETERMINISTIC GUIDANCE, WHICH CLUSTER CLOSELY TOGETHER THROUGH  
EARLY TUESDAY. THOUGH THERE IS NOW CONSENSUS ON THAT EVEN  
HAPPENING, THERE REMAINS DISAGREEMENT ON HOW THIS UPPER LOW  
MEANDERS FOR THE REST OF THE WEEK JUST NORTH OF THE AREA. THE GEFS  
MEMBERS WERE CLOSER TO THE GFS/ECMWF/CANADIAN WHICH LINGER THE  
UPPER LOW BETWEEN 152-162W NEXT WED-FRI WHILE THE ECMWF ENSEMBLE  
MEMBERS MOSTLY ALLOW IT TO LIFT NORTHEASTWARD. STRONG  
DETERMINISTIC CONSENSUS AND LIKELY STRONG DOWNSTREAM RIDGING  
SUGGEST THAT THE SLOWER CLUSTER OF SOLUTIONS MAY BE MORE CORRECT.  
 
AS THE UPPER LOW DIVES SOUTHWARD AND LOWER LEVEL FLOW VEERS TO  
SOUTHEASTERLY, AN INCREASE IN MOISTURE IS EXPECTED OVER THE REGION  
NEXT WEEK. DEEP ITCZ MOISTURE MAY GET PULLED NORTHWARD AHEAD OF  
THE FRONT, WHICH MAY PUSH THROUGH THE WHOLE ISLAND CHAIN. SHOULD  
THE FRONT ACTUALLY MAKE IT EAST OF THE AREA, THEN THE NW FLOW  
BEHIND IT SHOULD LESSEN THE HEAVY RAIN THREAT. HOWEVER, GIVEN THE  
SPREAD IN THE ENSEMBLES (INCLUDING SOME MEMBERS FARTHER WEST THAN  
THE 00Z GFS/CANADIAN), THE MOISTURE AXIS COULD REMAIN OVER AT  
LEAST PART OF THE HAWAI'I LATER NEXT WEEK.  
 
FRACASSO  
 

 
 
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