124  
FXHW01 KWNH 231217  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
716 AM EST THU NOV 23 2017  
 
VALID 00Z FRI NOV 24 2017 - 00Z FRI DEC 01 2017  
 
THE PERSISTENT POSITIVE HEIGHT ANOMALIES TO THE NORTHWEST OF  
HAWAI'I WILL WEAKEN AND BE REPLACED BY AN UPPER LOW NEAR THE  
ALEUTIANS AND BERING SEA NEXT WEEK AS ELONGATED SW-NE TROUGHING  
REMAINS OVER THE 50TH STATE. 00Z GEFS/ECMWF ENSEMBLES SHOW THIS  
EVOLUTION RATHER NICELY WITH EXPECTED DETAIL DIFFERENCES. A BLEND  
OF THE 00Z GUIDANCE SHOULD SUFFICE THIS PERIOD.  
 
THE 1034MB SFC HIGH TO THE NORTHWEST OF THE REGION WILL BE  
REINFORCED THIS WEEKEND AND SLIDE SOUTHEASTWARD THEN EASTWARD  
ALONG 33N NEXT WEEK WHICH WILL MAINTAIN BREEZY/WINDY TRADES INTO  
NEXT WEEK. LIGHT TO SCATTERED WINDWARD/MAUKA SHOWERS ARE EXPECTED  
WITH ONLY SOME SPILLOVER TO LEEWARD AREAS POSSIBLE AS THE OVERALL  
AIRMASS REMAINS DRY. BY ABOUT NEXT, ENSEMBLES SHOW AN INCREASE IN  
COLUMN MOISTURE AS A REMNANT BOUNDARY LIFTS BACK TO THE NORTHWEST  
FROM NEAR THE ITCZ. TROUGHING OR EVEN A WEAKLY CLOSED LOW MAY  
RETROGRADE TO JUST WEST OF THE AREA MIDWEEK NEXT WEEK, WHICH COULD  
ACT TO INCREASE RAIN COVERAGE FROM SOUTHEAST TO NORTHWEST. THE  
GFS/ECMWF HAVE WAVERED ON HOW MUCH TO INCREASE PRECIPITABLE WATER  
VALUES AND THE LATEST 00Z ECMWF WAS MORE AGGRESSIVE THAN THE GFS  
AND ALSO A BIT MORE AGGRESSIVE THAN THE ENSEMBLE MEANS. A BLENDED  
SOLUTION MAY STILL BE APPROPRIATE SINCE THE PATTERN SUGGESTS THE  
POTENTIAL FOR AT LEAST SOME MODEST TO LOCALLY HEAVY RAIN NEXT  
WEEK. THIS MAY PERSIST THROUGH THE END OF THE WEEK AS THE  
ENSEMBLES MAINTAIN HIGHER THAN AVERAGE PW VALUES INTO DECEMBER,  
ESPECIALLY OVER THE BIG ISLAND/MAUI.  
 
FRACASSO  
 

 
 
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