030  
FXHW01 KWNH 051156  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
655 AM EST SUN NOV 05 2017  
 
VALID 00Z MON NOV 06 2017 - 00Z MON NOV 13 2017  
 
REX BLOCK PATTERN WITH AN AXIS WELL WEST OF HAWAII NORTH TO ALASKA  
IS FORECAST TO PROPAGATE SLOWLY WESTWARD THROUGH THE NEXT WEEK,  
KEEPING THE FLOW PATTERN ACROSS HAWAI'I RELATIVELY STABLE. UPPER  
RIDGING CENTERED OVERHEAD IS FORECAST BY ALL GUIDANCE TO SLOWLY  
WEAKEN THROUGH THE WEEK, ALTHOUGH, WEAKLY POSITIVE HEIGHT  
ANOMALIES ARE FORECAST BY THE ECMWF ENSEMBLE MEAN TO REMAIN IN  
PLACE ACROSS THE ISLANDS - LIKELY AN EFFECT OF THE UPSTREAM AREA  
OF STRONG NEGATIVE HEIGHT ANOMALIES NEAR 160-170E. AT THE SURFACE  
A WEAKENING HIGH INITIALLY CENTERED WELL NORTHEAST OF HAWAI'I WILL  
RESULT IN SLIGHTLY WEAKENING EASTERLIES AS THE PRESSURE GRADIENT  
LESSENS, FROM 20 KT TODAY TO 10-15 KT BY THE MIDDLE OF NEXT WEEK.  
THIS FLOW PATTERN WILL KEEP RELATIVELY LOW PRECIPITABLE WATER  
VALUES IN PLACE AS GUIDANCE SHOWS VERY DRY AIR (PWS NEAR OR EVEN  
LESS THAN 1 INCH) ORIGINATING IN THE NORTHEASTERN PACIFIC  
ADVECTING ACROSS HAWAI'I. THEREFORE, EXPECT SHOWERS TO BE  
GENERALLY FOCUSED ALONG WINDWARD TERRAIN, BECOMING A BIT MORE  
SPARSE THROUGH THE WEEK. A TROUGH FORECAST TO AMPLIFY ACROSS THE  
NORTHEASTERN PACIFIC BY EARLY-MID NEXT WEEK WILL FORCE THE TAIL  
END OF A COLD FRONT SOUTHWARD TOWARD THE ISLANDS, ALTHOUGH THE  
MODEL CONSENSUS IS THAT THE FRONT SHOULD REMAIN WELL NORTH OF THE  
ISLANDS THROUGH NEXT WEEKEND AS IT WASHES OUT.  
 
RYAN  
 

 
 
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