624  
FXHW01 KWNH 201211  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
711 AM EST MON NOV 20 2017  
 
VALID 00Z TUE NOV 21 2017 - 00Z TUE NOV 28 2017  
 
MODELS AND ENSEMBLES MAINTAIN A MEAN TROUGH ALOFT DURING THE  
PERIOD, GENERALLY ORIENTED NORTHEAST-SOUTHWEST OVER THE STATE. IN  
THIS PATTERN THE PRECIPITABLE WATER VALUES WILL LIKELY REMAIN  
BELOW NORMAL AT LEAST THROUGH THE WEEKEND. AS A RESULT  
WINDWARD-FOCUSED BUT OCCASIONAL LEEWARD SHOWER ACTIVITY SHOULD  
STAY ON THE LIGHTER SIDE. BUNDLES OF SHEARED SHORTWAVE ENERGY  
EMBEDDED WITHIN THE OVERALL MEAN TROUGH MAY PROVIDE A LITTLE EXTRA  
ORGANIZATION TO RAINFALL AT TIMES. TOWARD THE BEGINNING OF NEXT  
WEEK SOME GUIDANCE IS SUGGESTING A POTENTIAL FOR A NORTHWARD DRIFT  
OF MOISTURE TOWARD THE BIG ISLAND IN RESPONSE TO EVOLUTION OF  
ENERGY WITHIN THE UPPER TROUGH. THE SMALL SCALE OF THE SHORTWAVE  
ENERGY AND TYPICAL MODEL VERIFICATION SEVEN DAYS OUT IN TIME  
COMBINE TO YIELD LOW CONFIDENCE IN A SPECIFIC SCENARIO. THUS AT  
THIS TIME WOULD RECOMMEND A COMPROMISE FOR RESOLVING GUIDANCE  
DIFFERENCES BY NEXT MONDAY.  
 
EXPECT LOW LEVEL WINDS INITIALLY FROM THE NORTH TO BECOME  
NORTHEASTERLY OVER THE NEXT DAY OR SO AS LOW PRESSURE TO THE  
NORTHEAST OF THE STATE CONTINUES LIFTING AWAY AND A CENTRAL  
PACIFIC SURFACE RIDGE EXTENDS SOUTHEASTWARD. A MORE TYPICAL  
EAST-NORTHEASTERLY TRADE PATTERN WILL DEVELOP LATE WEEK ONWARD AS  
HIGH PRESSURE CONTINUES TO PUSH SOUTHEASTWARD. GUIDANCE IS  
CONSISTENT IN SHOWING A FAIRLY TIGHT PRESSURE GRADIENT WITH  
BRISK/WINDY TRADES LATE THIS WEEK AND PERHAPS TO SOME EXTENT INTO  
THE WEEKEND. BY NEXT WEEKEND AND EARLY NEXT WEEK THE 00Z GEFS  
MEAN DIFFERS FROM OTHER GUIDANCE IN HOLDING HIGH PRESSURE FARTHER  
NORTH AND THEN NORTHWEST OF CONSENSUS BUT THIS APPEARS TO HAVE  
ONLY MODEST IMPACT ON THE SURFACE PATTERN OVER THE ISLANDS.  
 
RAUSCH  
 

 
 
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