141  
FXHW01 KWNH 221219  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
818 AM EDT SAT JUL 22 2017  
 
VALID 00Z SUN JUL 23 2017 - 00Z SUN JUL 30 2017  
 
TROPICAL STORM FERNANDA, CURRENTLY ABOUT 600 MILES EAST OF HAWAI'I  
PER THE LATEST CPHC ADVISORY, IS FORECAST TO CONTINUE WEAKENING  
AND BECOME POST-TROPICAL BY LATE TODAY AS IT CONTINUES ON A  
WEST-NORTHWESTWARD PATH. THE REMNANT LOW IS FORECAST TO PASS NORTH  
OF THE ISLANDS SUNDAY INTO MONDAY. MODELS HAVE COME INTO BETTER  
AGREEMENT SHOWING A WEAKER LOW CENTER WITH A TRACK JUST NORTH OF  
HAWAI'I. A BRIEF DISRUPTION TO THE EASTERLY TRADES IS POSSIBLE AS  
THE SYSTEM PASSES BY, BUT THE TRADES SHOULD QUICKLY RESUME IN ITS  
WAKE. AN INCREASE IN PRECIPITABLE WATER VALUES AHEAD OF THE SYSTEM  
MAY ALSO INCREASE SHOWER ACTIVITY BY SUNDAY AND MONDAY, ALTHOUGH  
THE CORE OF DEEPER MOISTURE ASSOCIATED WITH THE SYSTEM IS FORECAST  
BY BOTH THE GFS AND THE ECMWF TO REMAIN NORTH OF THE ISLANDS.  
PLEASE REFER TO THE CPHC ADVISORIES FOR THE LATEST INFORMATION ON  
FERNANDA.  
 
OTHERWISE, AN EXPANSIVE SURFACE HIGH IS FORECAST BY ALL GUIDANCE  
TO REMAIN ANCHORED WELL NORTHEAST OF HAWAI'I THROUGH THE NEXT  
WEEK, WHICH SHOULD KEEP 10-20 KT SURFACE EASTERLIES PREVALENT  
ACROSS THE ISLANDS WITH THE TYPICAL ASSOCIATED SHOWER ACTIVITY.  
TROPICAL STORM GREG IS FORECAST BY NHC TO CONTINUE ON A GENERALLY  
WESTWARD TO WEST-NORTHWESTWARD TRACK THROUGH THE NEXT SEVERAL  
DAYS. GREG IS FORECAST TO BECOME POST-TROPICAL BY LATE WEDNESDAY,  
STILL WELL EAST OF HAWAI'I. MODELS SHOW SOME SPREAD WITH RESPECT  
TO WHETHER THE REMNANT LOW FROM GREG WILL MAKE IT TO HAWAI'I  
BEFORE DISSIPATING. THE ECMWF AND GEM GLOBAL ARE QUITE A BIT  
FASTER THAN THE GFS AND BRING GREG'S REMNANT LOW TO JUST EAST OF  
THE BIG ISLAND BY SATURDAY AFTERNOON. ENSEMBLES SHOW A RATHER  
LARGE RANGE OF SPREAD, BUT AT THIS TIME THERE SEEMS TO BE A  
SOMEWHAT GREATER CLUSTERING OF EC/GEFS/CMC ENSEMBLE MEMBERS AROUND  
THE FASTER DETERMINISTIC ECMWF/GEM SOLUTIONS.  
 
RYAN  
 

 
 
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