915  
FXHW01 KWNH 131213  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
812 AM EDT FRI OCT 13 2017  
 
VALID 00Z SAT OCT 14 2017 - 00Z SAT OCT 21 2017  
 
LATEST GUIDANCE IS CONSISTENT IN SHOWING A PRONOUNCED  
STRENGTHENING OF TRADES AS A SURFACE TROUGH INITIALLY OVER THE  
WESTERN ISLANDS DEPARTS FROM THE AREA. SURFACE HIGH PRESSURE  
EXPECTED TO SETTLE TO THE NORTH OF THE STATE LATE SUNDAY INTO NEXT  
WEEK SHOULD BEGIN TO WEAKEN SOMEWHAT TOWARD NEXT FRIDAY. TRADES  
WILL LIKELY STILL BE BRISK AT THAT TIME BUT WITH SOMEWHAT LESS  
WINDY CONDITIONS THAN EARLY-MID WEEK. INTO THE EARLY PART OF THIS  
WEEKEND, RAIN AND POTENTIAL THUNDERSTORMS MAY BE LOCALLY HEAVY IN  
ASSOCIATION WITH A WEAKNESS ALOFT AND A BAND OF 1.50-2.00 INCH  
PRECIPITABLE WATER VALUES PASSING OVER THE STATE. DRIER AIR WILL  
MOVE IN LATE WEEKEND INTO NEXT WEEK, LEADING TO A LIGHTER TREND  
FOR GENERALLY WINDWARD-FOCUSED RAINFALL. TOWARD THURSDAY-FRIDAY  
THERE IS STILL SOME DISAGREEMENT OVER THE POTENTIAL EVOLUTION/PATH  
OF SOME WEAK UPPER LEVEL ENERGY WITH CORRESPONDING DIFFERENCES IN  
THE NORTHWARD EXTENT OF LOWER LATITUDE MOISTURE. AMONG CURRENT  
GUIDANCE THE 00Z GFS/GEFS MEAN SHOW THE BEST DEFINED UPPER LEVEL  
FEATURE WITH MORE MOISTURE REACHING AT LEAST AS FAR NORTH AS THE  
BIG ISLAND. THE 06Z GFS MADE A SIGNIFICANT ADJUSTMENT IN THE 00Z  
ECMWF DIRECTION, WITH A STRONGER UPPER RIDGE JUST TO THE NORTH  
LEADING TO A MORE SUPPRESSED/SHEARED WEAKNESS ALOFT AND  
MAINTENANCE OF PRECIPITABLE WATER VALUES AT VALUES BELOW  
CLIMATOLOGY. THE FULL RANGE OF MODEL/ENSEMBLE GUIDANCE SUGGESTS  
THERE IS STILL ROOM FOR SOME ENERGY ALOFT/MOISTURE RETURN BUT THAT  
THE MOST LIKELY SCENARIO IS SOMEWHAT MORE THAN HALFWAY TOWARD THE  
DRIER 06Z GFS/00Z ECMWF VERSUS THE 00Z GFS/GEFS MEAN.  
 
RAUSCH  
 

 
 
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