477  
FXHW01 KWNH 161234  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
833 AM EDT MON OCT 16 2017  
 
VALID 00Z TUE OCT 17 2017 - 00Z TUE OCT 24 2017  
 
MODELS AND ENSEMBLES SHOW GENERALLY GOOD AGREEMENT ON THE LARGE  
SCALE PATTERN ACROSS THE CENTRAL PACIFIC THROUGH THE NEXT WEEK.  
UPPER RIDGE INITIALLY NORTHWEST OF HAWAII WILL MOVE A BIT EAST  
OVER THE ISLANDS AS IT GRADUALLY WEAKENS. MEANWHILE, AN UPPER LOW  
WELL NORTHEAST OF THE STATE WILL ALSO SLOWLY WEAKEN OVER THE NEXT  
WEEK, HAVING VERY LITTLE IN THE WAY OF SENSIBLE WEATHER IMPACTS  
OVER HAWAII. LOW-LEVEL EAST-NORTHEASTERLY FLOW OF 15-25 KT WILL  
PERSIST ACROSS THE ISLANDS THROUGH MOST OF THE NEXT WEEK, AS A  
SURFACE HIGH REMAINS ANCHORED NORTH OF THE STATE. A RELATIVELY DRY  
AIR MASS WILL KEEP SHOWER ACTIVITY LIMITED TO THE FAVORED WINDWARD  
TERRAIN AREAS THROUGH MOST OF THE WEEK. THE PATTERN ACROSS THE  
CENTRAL PACIFIC SHOULD BEGIN TO CHANGE BY LATE NEXT WEEKEND AS  
MOST MODELS AND ENSEMBLES SHOW A SHORTWAVE AMPLIFYING ACROSS THE  
NORTH CENTRAL PACIFIC, WHICH COULD PUSH A COLD FRONT SOUTHWARD IN  
THE GENERAL DIRECTION OF HAWAII. THERE IS A FAIRLY LARGE DEGREE OF  
SPREAD, HOWEVER, AS TO THE EXACT EVOLUTION OF THE TROUGH, AND  
WHETHER A MORE FULL LATITUDE TROUGH AMPLIFIES NORTH OF HAWAII (AS  
SHOWN BY THE GFS AS WELL AS THE GEFS/NAEFS/CMC ENSEMBLES) OR  
WHETHER A SOMEWHAT WEAKER WAVE MOVES EAST MORE QUICKLY (AS SHOWN  
BY THE CMC). THE 00Z ECMWF WAS GENERALLY IN THE MIDDLE OF THESE  
TWO EXTREMES. THE EXACT EVOLUTION OF THIS TROUGH WILL HAVE A  
SIGNIFICANT IMPACT ON THE ORIENTATION OF THE SURFACE COLD FRONT  
AND HOW MUCH MOISTURE GETS DRAWN NORTHWARD INTO IT. NONETHELESS,  
THERE SHOULD BE SOME TYPE OF WAVE AMPLIFYING NORTH OF HAWAII BY  
LATE IN THE WEEKEND, WHICH COULD PUSH A FRONT TOWARD THE ISLANDS,  
BUT IT REMAINS UNCLEAR ON HOW QUICKLY THE FRONT WILL MOVE SOUTH  
TOWARD THE ISLANDS AND HOW MUCH PRECIPITATION COULD RESULT ACROSS  
HAWAII DURING THIS FORECAST PERIOD.  
 
RYAN  
 

 
 
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