236  
FXHW01 KWNH 171227  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
726 AM EST SUN DEC 17 2017  
 
VALID 00Z MON DEC 18 2017 - 00Z MON DEC 25 2017  
   
..HEAVY RAIN THREAT NEXT WEEK
 
 
AN UPPER LOW WILL CONTINUE TO WEAKEN WHILE GRADUALLY LIFTING  
NORTHEASTWARD AWAY FROM THE ISLANDS ON SUNDAY, BUT THEN AN  
AMPLIFYING LONGWAVE TROUGH IS EXPECTED TO ALIGN OVER THE STATE  
WHILE A DOWNSTREAM RIDGE BUILDS OFF THE CALIFORNIA COAST EARLY TO  
MID WEEK. A RICH SUPPLY OF DEEP TROPICAL MOISTURE (PRECIPITABLE  
WATER VALUES 2 TO 3 STANDARD DEVIATIONS ABOVE NORMAL) AHEAD OF THE  
LEADING COLD FRONT WILL HEIGHTEN THE THREAT FOR HEAVY RAINFALL  
WHILE THE BOUNDARY PRESSES SOUTH/SOUTHEASTWARD THROUGH THE ISLANDS  
TUESDAY AND WEDNESDAY. THE THREAT FOR HEAVY RAIN SHOULD DIMINISH  
LATE IN THE WEEK ONCE THE MEAN THROUGH AXIS AND FEED OF MOISTURE  
SHIFT EASTWARD THURSDAY INTO FRIDAY.  
 
DETERMINISTIC AND ENSEMBLE GUIDANCE CONTINUE TO SHOW GOOD  
AGREEMENT WITH THE LARGE SCALE PATTERN SETTING UP OVER THE ISLANDS  
THIS WEEK, AND ARE EVEN SHOWING MINIMAL SPREAD WITH THE DETAILS OF  
EMBEDDED CLOSED LOWS WITHIN THE AMPLIFYING LONGWAVE TROUGH. THERE  
ALSO APPEARS TO BE ABOVE AVERAGE AGREEMENT WITH THE TIMING OF THE  
TROUGH AXIS SHIFTING EASTWARD LATE THIS WEEK/NEXT WEEKEND..  
 
GERHARDT  
 

 
 
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