970  
FXHW01 KWNH 031215  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
714 AM EST SUN DEC 03 2017  
 
VALID 00Z MON DEC 04 2017 - 00Z MON DEC 11 2017  
 
A STRONG UPPER-LEVEL RIDGE CENTERED WELL TO THE WEST OF HAWAI'I  
WILL HAVE DOWNSTREAM IMPACTS ACROSS THE NORTH/CENTRAL PACIFIC WITH  
PERSISTENT NEGATIVE HEIGHT ANOMALIES AND SOUTHWARD PENETRATION OF  
THE WESTERLIES TOWARD HAWAI'I. A SHORTWAVE IS FORECAST TO AMPLIFY  
NORTH OF THE ISLANDS MON-TUE, PUSHING A COLD FRONT SOUTHWARD  
ACROSS THE STATE. MODELS AND ENSEMBLES SHOW RELATIVELY LOW SPREAD  
SURROUNDING THIS FEATURE, AND CONFIDENCE IS ABOVE AVERAGE EARLY IN  
THE FORECAST PERIOD. WHILE PWAT VALUES WILL ALREADY BE RELATIVELY  
LOW (0.80-1.00 INCH), THE PASSAGE OF THE FRONT BY TUE WILL BRING  
EVEN DRIER AIR TO THE STATE, WITH FORECAST PWATS FORECAST TO DROP  
TO NEAR OR EVEN BELOW 0.50 INCH. GUSTY NORTHERLY TO NORTHEASTERLY  
WINDS OF 20-25 KT WILL LIKELY ALSO ACCOMPANY AND FOLLOW THE  
FRONTAL PASSAGE. THE LACK OF PREEXISTING MOISTURE AHEAD OF THE  
FRONT WILL LIKELY PRECLUDE ANY SIGNIFICANT SHOWER ACTIVITY  
ASSOCIATED WITH ITS PASSAGE. ANOTHER SHORTWAVE IS FORECAST TO  
AMPLIFY NORTH OF HAWAI'I BY WED, WITH A RATHER STRONG SURFACE  
CYCLONE FOR 30-35 DEG N ACCOMPANYING IT. MODELS AND ENSEMBLES ARE  
ALSO IN RELATIVELY GOOD AGREEMENT ON THIS SCENARIO WITH SOME  
DIFFERENCES SURROUNDING THE INTENSITY OF THE SYSTEM (00Z UKMET WAS  
STRONGEST WHILE THE CMC WAS WEAKEST). AT THIS TIME THE PREFERRED  
SOLUTION IS SOMEWHERE IN THE MIDDLE OF THE SPREAD, TOWARD A BLEND  
OF THE 00Z ECENS/GEFS/NAEFS. THE 06Z GFS SEEMS TO BE IN THIS  
VICINITY WHILE THE 00Z ECMWF IS A BIT FASTER THAN CONSENSUS. A  
WAVE ALONG THE FRONT MAY SLOW THE PROGRESSION TOWARD HAWAI'I BUT  
ANOTHER COLD FRONT SHOULD BE APPROACHING THE ISLANDS BY LATE IN  
THE WEEK, WITH AN ASSOCIATED INCREASE IN MOISTURE INCREASING  
PRECIPITATION CHANCES.  
 
RYAN  
 

 
 
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