007  
FXHW01 KWNH 121221  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
820 AM EDT THU OCT 12 2017  
 
VALID 00Z FRI OCT 13 2017 - 00Z FRI OCT 20 2017  
 
TRADES WILL BECOME GRADUALLY STRONGER OVER THE NEXT FEW DAYS AS A  
SURFACE TROUGH INITIALLY OVER THE STATE MOVES TO THE WEST AND  
EASTERN PACIFIC HIGH PRESSURE DRIFTS SOUTHWESTWARD, SETTLING OVER  
A POSITION NEAR 35N LATITUDE. EXPECT STRONGEST WINDS DURING THE  
SUNDAY-THURSDAY PERIOD. FROM NOW INTO THE WEEKEND THERE WILL BE  
THE POTENTIAL FOR SOME LOCALLY HEAVY RAINFALL WITH THE COMBINATION  
OF THE EARLY PERIOD SURFACE TROUGH, AN UPPER LEVEL WEAKNESS, AND  
PRECIPITABLE WATER VALUES IN THE 1.50-2.00 INCH RANGE. BEST FOCUS  
FOR RAINFALL WILL BE WINDWARD LOCATIONS BUT SOME ACTIVITY MAY  
STRAY INTO LEEWARD AREAS AS WELL. GUIDANCE AGREES WELL THAT DRIER  
AIR WILL MOVE INTO THE REGION FOR MONDAY THROUGH AT LEAST  
WEDNESDAY SO EXPECT LIGHTER TOTALS FOR WINDWARD-FOCUSED RAINFALL  
IN THAT TIME FRAME. BY NEXT THURSDAY MODELS BEGIN TO DIFFER  
REGARDING A POSSIBLE INCREASE IN MOISTURE OVER THE BIG ISLAND AND  
VICINITY AS SHEARED UPPER LEVEL ENERGY TO THE EAST OF THE AREA MAY  
CLOSE OFF A RETROGRADING WEAK UPPER LOW. CURRENTLY GFS RUNS ARE  
FARTHER WEST WITH THIS UPPER FEATURE THUS BRINGING MORE MOISTURE  
INTO THE SOUTHEASTERN ISLANDS THAN THE 00Z ECMWF. IN VARYING WAYS  
THE 00Z ECMWF MEAN AND 12Z/11 ECMWF OFFER INTERMEDIATE SOLUTIONS  
FOR THE UPPER LEVEL FEATURE/LOWER LEVEL MOISTURE INCREASE. LOW  
PREDICTABILITY OF SUCH A SMALL SCALE EVOLUTION AT THAT TIME FRAME  
RECOMMENDS A FORECAST HALFWAY BETWEEN THE 00Z/06Z GFS AND 00Z  
ECMWF EXTREMES.  
 
RAUSCH  
 

 
 
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