040  
FXHW01 KWNH 121218  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
718 AM EST TUE DEC 12 2017  
 
VALID 00Z WED DEC 13 2017 - 00Z WED DEC 20 2017  
 
COLD FRONT WILL MOVE ACROSS HAWAI'I TODAY AS AN UPPER TROUGH  
AMPLIFIES NORTH/NORTHEAST OF THE ISLANDS. AN UPPER LOW WILL FORM  
JUST TO THE EAST OF HAWAI'I WED NIGHT/THU AND THEN SLOWLY DRIFT  
WEST-NORTHWESTWARD INTO THE WEEKEND. BY SUN-MON THE UPPER LOW  
SHOULD LIFT NORTHWARD AND BECOME ABSORBED INTO A POSITIVELY TILTED  
TROUGH AXIS EXTENDING FROM JUST NORTHWEST OF HAWAI'I TO THE GULF  
OF ALASKA. THAT MAY AGAIN CLOSE OFF AN UPPER LOW ON ITS SOUTHWEST  
TAIL TO THE NORTH OF THE REGION NEXT TUESDAY. A BLEND OF THE  
RECENT 06Z GFS AND 00Z ECMWF (BOTH NEAR THEIR ENSEMBLE MEANS)  
OFFERS A REASONABLE STARTING SOLUTION.  
 
SCATTERED SHOWERS AND PERHAPS EVEN A FEW LOCALIZED AREAS OF HEAVY  
RAINFALL WILL ACCOMPANY THE FRONT TODAY INTO TOMORROW. BEHIND THE  
FRONT, BREEZY NORTHWEST WINDS WILL BRING IN DRIER AND COOLER AIR  
AND VEER TO THE NORTH AND NORTHEAST TOMORROW INTO THURSDAY WHEN  
WINDS MAY EXCEED 30 KTS.  
 
TREND HAS BEEN TO KEEP MOST BUT NOT ALL OF THE MODERATE/HEAVY RAIN  
ASSOCIATED WITH THE UPPER LOW THIS WEEKEND JUST NORTH OF THE AREA  
AS THE MAIN MOISTURE AXIS TO THE EAST WRAPS AROUND FROM THE NORTH  
INTO THE ISLANDS. 00Z ECMWF ENSEMBLE PROBABILITIES OF EXCEEDING 1  
INCH QPF IN A GIVEN 72 HOUR PERIOD WAS NO LARGER THAN ABOUT 15-20%  
ANYWHERE OVER THE ISLANDS.  
 
AS THE NEXT UPPER TROUGH AMPLIFIES NORTHWEST OF HAWAI'I BY EARLY  
NEXT WEEK, ADDITIONAL RAIN WILL BE PROBABLE GIVEN THE LOCATION OF  
THE UPPER LOW OR SHARP TROUGH TO THE WEST OF THE REGION.  
 
FRACASSO  
 

 
 
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