726  
FXHW01 KWNH 271218  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
717 AM EST SAT JAN 27 2018  
 
VALID 00Z SUN JAN 28 2018 - 00Z SUN FEB 04 2018  
 
AHEAD OF A SHORTWAVE TROUGH ALOFT AND WEAKENING SURFACE FRONT  
CROSSING THE STATE THIS WEEKEND, THE BIG ISLAND AND VICINITY WILL  
CONTINUE TO BE ON THE WESTERN EDGE OF AN AREA CONTAINING ENHANCED  
DEEP MOISTURE WHICH WILL PROMOTE RAINFALL OF VARYING INTENSITY.  
MODELS STILL VARY WITH PRECISE WESTWARD EXTENT OF HIGHEST  
MOISTURE, FAVORING AN INTERMEDIATE SOLUTION. PROGRESSION OF THESE  
FEATURES WILL BRING A DRYING TREND OVER THE STATE FOR MOST OF  
MONDAY-TUESDAY WITH RELATIVELY LIGHT EASTERLY LOW LEVEL WINDS  
TURNING SOUTHEASTERLY, AND THEN STRENGTHENING SOMEWHAT FROM THE  
SOUTH/SOUTHWEST AS A FRONT APPROACHES FROM THE WEST.  
 
FOR THIS LATE TUESDAY-WEDNESDAY FRONT SUPPORTED BY DEVELOPING MEAN  
TROUGHING ALOFT NORTHWEST OF THE STATE, THE 00Z ECMWF IS FASTER  
THAN 00Z/06Z GFS RUNS BUT WITH DIFFERENCES ALOFT NOT COMPLETELY  
MATCHING UP WITH RESPECTIVE SURFACE DETAILS AND OTHER GUIDANCE  
AVERAGING A LITTLE SLOWER THAN THE ECMWF. THUS A COMPROMISE  
TIMING APPEARS REASONABLE. THE FRONT SHOULD BRING SOME LOCALLY  
MODERATE-HEAVY RAINFALL INTO THE FAR NORTHWESTERN ISLANDS BUT  
ACTIVITY SPREADING SOUTHEAST WILL LIKELY TREND A BIT LIGHTER FOR A  
TIME AS DYNAMICS LIFT NORTHEASTWARD.  
 
HOWEVER IN SPITE OF THIS BRIEF LIGHTER TREND, STALLING OF THIS  
FRONT ALONG WITH THE APPROACH OF UPSTREAM ENERGY ALOFT AND ANOTHER  
COLD FRONT SHOULD BE A FAVORABLE SETUP TO MAINTAIN MOIST FLOW OVER  
THE ISLANDS FOR THE LATTER HALF OF THE WEEK. THUS MORE EPISODES  
OF ENHANCED RAINFALL ARE POSSIBLE. AS WAS THE CASE YESTERDAY,  
SIGNIFICANT TIMING DIFFERENCES DEVELOP FOR THIS LATTER FRONT WITH  
THE GFS CONTINUING TO BE MORE PROGRESSIVE THAN MOST OTHER  
GUIDANCE. TODAY THE 00Z GEFS MEAN IS MORE SIMILAR TO GFS RUNS  
THOUGH. THE GFS HAS SLOWED SIGNIFICANTLY FROM ITS RUNS OF 24  
HOURS AGO, SEEMINGLY PROVIDING MORE SUPPORT FOR MAINTAINING A  
SOLUTION PERHAPS 2/3 TOWARD THE SLOWER CLUSTER OF GUIDANCE.  
 
RAUSCH  
 

 
 
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