162  
FXHW01 KWNH 101214  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
714 AM EST SUN DEC 10 2017  
 
VALID 00Z MON DEC 11 2017 - 00Z MON DEC 18 2017  
 
AN ACTIVE WEATHER PATTERN WILL REMAIN IN PLACE ACROSS THE CENTRAL  
PACIFIC OVER THE NEXT WEEK. COLD FRONT PUSHING ACROSS HAWAI'I  
TODAY IS EXPECTED TO WASH OUT AS IT REACHES THE SOUTHERN ISLANDS  
TONIGHT. A COUPLE DAYS OF RELATIVELY QUIET WEATHER WILL FOLLOW  
BEFORE ANOTHER UPPER SHORTWAVE AMPLIFIES NORTH OF THE STATE  
MON-TUE. MODELS AND ENSEMBLES CONTINUE TO SHOW GOOD AGREEMENT ON  
THE INITIAL AMPLIFICATION OF THIS SYSTEM. GUIDANCE ALSO AGREES ON  
SHOWING THE WAVE RAPIDLY AMPLIFYING AND THEN AN UPPER LOW CUTTING  
OFF NEAR OR EVEN OVER HAWAI'I BY THU. AFTER CUTTING OFF, GUIDANCE  
GENERALLY SHOW THE FEATURE RETROGRADING WESTWARD, WITH THE ECMWF  
CONTINUING TO BE THE MOST AGGRESSIVE WITH THIS, ALTHOUGH THE GFS  
HAS MOVED TOWARD THE ECMWF SOLUTION. EXPECT THE FRONTAL BOUNDARY  
TO STALL SOUTH/EAST OF HAWAI'I AS THE UPPER LOW CUTS OFF.  
CONFIDENCE IS INCREASING THAT THE UPPER LOW RETROGRESSION, WILL  
ALLOW HIGHER PWATS (1.30-1.70") TO BE ADVECTED NORTH ACROSS THE  
STATE BY LATE IN THE WEEK. AS A RESULT, THE ECMWF AND GFS BOTH  
SHOW THE POTENTIAL FOR HEAVY PRECIPITATION BY LATE IN THE WEEK,  
ESPECIALLY ACROSS THE EASTERN ISLANDS WHERE 20-30 KT EASTERLY  
LOW-LEVEL FLOW WILL TAKE HOLD. ECENS PROBABILITIES FOR HEAVIER  
RAINFALL AMOUNTS LATE IN THE WEEK HAVE INCREASED COMPARED TO  
YESTERDAY, WITH A 25-35 PERCENT CHANCE OF EXCEEDING 1 INCH ACROSS  
PORTIONS OF THE BIG ISLAND AND MAUI DURING THE 48-HOUR PERIOD  
ENDING 12Z SAT, AND A 10-20 PERCENT CHANCE OF EXCEEDING 2 INCHES  
DURING THAT TIME FRAME. GIVEN THE MODEL TRENDS AND IMPROVING  
CONSENSUS, CONFIDENCE IS INCREASING IN THE POTENTIAL FOR AT LEAST  
LOCALLY HEAVY RAINFALL ACROSS PORTIONS OF THE BIG ISLAND AND MAUI  
BY LATE IN THE WEEK.  
 
BY NEXT WEEKEND, MODELS/ENSEMBLES ARE IN AGREEMENT THAT THE UPPER  
LOW WILL BECOME ABSORBED INTO AN AMPLIFYING FULL-LATITUDE  
SHORTWAVE AXIS EXTENDING FROM JUST WEST OF HAWAI'I TO NEAR 50 DEG  
NORTH. THIS WILL KEEP SOUTHEASTERLY MOIST LOW-LEVEL FLOW IN PLACE  
(ESPECIALLY ACROSS THE EASTERN ISLANDS), WITH NUMEROUS SHOWERS  
POSSIBLE THROUGH THE WEEKEND  
 
RYAN  
 

 
 
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