439  
FXHW01 KWNH 191221  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
820 AM EDT THU OCT 19 2017  
 
VALID 00Z FRI OCT 20 2017 - 00Z FRI OCT 27 2017  
   
..HEAVY RAIN THREAT FOR NEXT WEEK
 
 
BREEZY TRADES WILL SLOWLY SUBSIDE BY THE WEEKEND AS A 1034MB  
SURFACE HIGH (06Z OPC ANALYSIS) WEAKENS AND MOVES SOUTHEASTWARD  
AND THEN EASTWARD ALONG 33N LATER THIS WEEK. GENERALLY LIGHT  
WINDWARD/MAUKA SHOWERS ARE EXPECTED. NEXT WEEK, A TROUGH IS  
FORECAST TO DIG ALONG/PAST 165W NORTH OF 35N (MON 12Z) BUT THE  
ENSEMBLES (AND DETERMINISTIC MODELS) CONTINUE TO DIVERGE ON  
WHETHER TO CONTINUE DIGGING IT TO/SOUTH OF 30N OR BEGIN TO LIFT IT  
BACK EASTWARD THEN NORTHEASTWARD (GENERALLY NORTH OF 30N). THE 00Z  
MODELS HAVE COMPLETELY FLIPPED SINCE 24 HRS AGO AND NOW THE ECMWF  
WAS MOST AGGRESSIVE WHILE THE GFS/CANADIAN AND EVEN UKMET WERE  
QUICKER THAN THE ECMWF (BUT AT LEAST MORE CONSISTENT). THE 00Z  
ECMWF LIES ON THE MOST EDGE OF THE MULTI-CENTER ENSEMBLE SPREAD  
AND IS NOT PREFERRED AT THIS TIME, GIVEN THE UNCERTAINTY AND  
INCONSISTENCY. THE 06Z GFS AND 00Z CANADIAN ALIGN NEAR THE UKMET  
TROUGH AXIS AND ARE THE PREFERRED CLUSTER. THIS ALSO LIES NEAR THE  
06Z GEFS MEAN AND 00Z ECMWF ENSEMBLE MEAN. THIS WOULD TAKE THE  
ASSOCIATED SURFACE FRONT INTO THE NW ISLANDS AROUND NEXT TUESDAY  
BUT IT IS UNCLEAR HOW MUCH OF A SE PROGRESSION IT WOULD MAKE.  
NEVERTHELESS, SOUTHEAST FLOW SHOULD INCREASE MOISTURE INTO THE  
WHOLE ISLAND CHAIN WHICH MAY SUPPORT SEVERAL DAYS OF WIDESPREAD  
SHOWERS AND EMBEDDED HEAVIER RAIN.  
 
FRACASSO  
 

 
 
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