930  
FXHW01 KWNH 291215  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
714 AM EST MON JAN 29 2018  
 
VALID 00Z TUE JAN 30 2018 - 00Z TUE FEB 06 2018  
 
EXPECT A PERIOD OF RELATIVELY DRY CONDITIONS EARLY THIS WEEK WITH  
THE DEPARTURE OF THE SHORTWAVE TROUGH INITIALLY OVER THE BIG  
ISLAND. ANY LIGHT SHOWERS THAT DEVELOP SHOULD VARY IN FOCUS  
MONDAY-TUESDAY AS LOW LEVEL WINDS TRANSITION FROM LIGHT TRADES TO  
LIGHT/VARIABLE AND BY TUESDAY SOUTHERLY/SOUTHWESTERLY WITH THE  
APPROACH OF A COLD FRONT. GUIDANCE AGREES FAIRLY WELL THAT THIS  
FRONT WILL BRING THE POTENTIAL FOR AREAS OF LOCALLY MODERATE-HEAVY  
RAINFALL INTO THE NORTHERN AND CENTRAL ISLANDS LATE TUESDAY  
ONWARD. THE FRONT WILL LIKELY DISSIPATE BUT PERSISTENCE OF MEAN  
TROUGHING ALOFT TO THE WEST/NORTHWEST SHOULD HOLD THE AXIS OF  
ENHANCED MOISTURE IN PLACE OVER AT LEAST PORTIONS OF THE STATE  
THROUGH THE WEEKEND AND POSSIBLY INTO NEXT WEEK. AS HAS BEEN THE  
CASE IN RECENT DAYS, GFS/GEFS MEAN RUNS STILL SHOW LOWER HEIGHTS  
ALOFT ON THE SOUTHEAST SIDE OF THE UPPER TROUGH COMPARED TO MOST  
OTHER GUIDANCE ESPECIALLY FROM SATURDAY ONWARD. INTO THE WEEKEND  
THIS HAS THE EFFECT OF THE GFS-BASED GUIDANCE SHOWING MORE FOCUSED  
MOISTURE/RAINFALL OVER THE ISLANDS. THEN BY NEXT SUNDAY-MONDAY  
THE GFS PUSHES A FRONT TOWARD AND EVENTUALLY THROUGH THE AREA  
WHILE ECMWF RUNS SHOW MUCH SLOWER PROGRESSION. SIMILAR TO  
YESTERDAY THE 00Z CMC SHOWS PROGRESSION OF A SURFACE BOUNDARY EVEN  
THOUGH ITS UPPER TROUGH IS NOT AS DEEP AS THE GFS. OVERALL WOULD  
RECOMMEND A COMPROMISE SOLUTION FOR MOISTURE/RAINFALL INTO THE  
WEEKEND AS THE GENERAL PATTERN APPEARS FAVORABLE FOR RAINFALL AND  
MULTI-DAY ECMWF TRENDS APPEAR WETTER THOUGH NOT WITH THE FOCUS OF  
THE GFS. THEN THE RECENT TENDENCY FOR GFS RUNS TO SLOW DOWN  
FRONTS RELATIVE THEIR DAYS 6-7 FORECASTS WOULD RECOMMEND LEANING  
SOMEWHAT MORE IN THE ECMWF/ECMWF MEAN DIRECTION BY SUNDAY-MONDAY.  
 
RAUSCH  
 

 
 
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