938  
FXHW01 KWNH 141220  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
719 AM EST THU DEC 14 2017  
 
VALID 00Z FRI DEC 15 2017 - 00Z FRI DEC 22 2017  
   
..HEAVY RAIN THREAT NEXT WEEK
 
 
AN UPPER LOW WILL EAST OF THE ISLANDS WILL SLOWLY DRIFT  
WEST-NORTHWESTWARD TOMORROW INTO SATURDAY, PASSING JUST NORTH OF  
OAHU. BY SUNDAY THE UPPER LOW IS FORECAST TO LIFT NORTHWARD AND  
BECOME ABSORBED INTO THE FLOW AHEAD OF AN APPROACHING TROUGH FROM  
THE NORTHWEST. THAT TROUGH MAY CLOSE OFF ONE OR TWO UPPER LOWS  
EARLY NEXT WEEK - ONE TO THE NORTH OF THE REGION AROUND 35N/160W  
AND PERHAPS ANOTHER TO THE NORTHWEST OF THE KAUAI. GFS/UKMET WERE  
QUICKER WITH THE TROUGH THAN THE ECMWF/CANADIAN BUT GIVEN THE  
UNCERTAINTY IN EVOLUTION PREFER A CONSENSUS POSITION BETWEEN THE  
TWO CAMPS WHICH IS A BIT SLOWER THAN THE ENSEMBLE MEANS. ENSEMBLES  
AND MOST DETERMINISTIC SOLUTIONS THEN SHOW REINFORCING TROUGHING  
FROM THE NORTHWEST NEXT WED/THU WITH PERHAPS YET ANOTHER UPPER LOW  
JUST TO THE NORTH OF THE REGION.  
 
BREEZY NORTHEAST MAY EXCEED 30 KTS WITH HIGHER GUSTS INTO TOMORROW  
MORNING BEFORE THE CLOSED LOW APPROACHES FROM THE EAST. MOISTURE  
WILL WRAP BACK AROUND THE SURFACE LOW FROM THE NORTH BUT THE  
HEAVIEST RAIN ON THE EAST SIDE OF THE UPPER LOW WILL REMAIN  
DISPLACED TO THE NORTHEAST OF THE REGION OVER THE NEXT SEVERAL  
DAYS.  
 
THE NEXT UPPER TROUGH OR WEAK UPPER LOW NEXT WEEK WILL LIKELY DRAW  
DEEP TROPICAL MOISTURE FROM THE ITCZ AND HAS THE POTENTIAL FOR  
MUCH MORE PRECIPITATION GIVEN ITS LOCATION. DETERMINISTIC MODELS  
STILL SHOW SEVERAL INCHES OF RAIN OVER SOME OF THE ISLANDS NEXT  
TUE-THU AHEAD OF THE FRONT WELL TO THE NORTHWEST. 00Z ECMWF  
ENSEMBLES AND 06Z GEFS ENSEMBLES NOW SHOW A PROBABILITY OF AT  
LEAST AN INCH OF PRECIPITATION EXCEEDING 60-80% IN THE 72 HRS  
ENDING 00Z/22 OVER THE BIG ISLAND AND MAUI. THIS WAS A BIG  
INCREASE FROM JUST 24 HRS AGO.  
 
FRACASSO  
 

 
 
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