137  
FXHW01 KWNH 271239  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
739 AM EST MON NOV 27 2017  
 
VALID 00Z TUE NOV 28 2017 - 00Z TUE DEC 05 2017  
   
..HEAVY RAIN LIKELY THIS WEEK
 
 
A SURFACE HIGH TO THE NORTH OF THE REGION WILL SLIDE EASTWARD  
WHICH SHOULD MAINTAIN BREEZY/WINDY TRADES FOR THE NEXT FEW DAYS.  
DEEP MOISTURE FROM THE ITCZ WILL ALSO SURGE NORTHWARD RESULTING IN  
THE POTENTIAL FOR HEAVY RAINFALL EARLY TO MID-WEEK ACROSS THE BIG  
ISLAND AND MAUI. LATER IN THE WEEK, ANOTHER TROUGH AND POTENTIAL  
SURFACE LOW WILL SLIDE CLOSE TO OR OVER THE WESTERN ISLANDS WHICH  
SHOULD SPREAD THE HEAVY RAINFALL NORTHWESTWARD BY NEXT WEEKEND.  
 
THERE REMAINS SIGNIFICANT SPREAD AMONGST THE OPERATIONAL MODELS ON  
WHERE UPPER TROUGHING SETS UP NEAR THE ISLANDS TOWARDS THE END OF  
THE WEEK. WHILE THE 06Z OPERATIONAL GFS RUN HAS COME FARTHER WEST  
THAN IT'S PREVIOUS 00Z RUN, BOTH ARE STILL EAST OF THE ECMWF/CMC.  
ENSEMBLES (INCLUDING MOST OF THE GEFS ENSEMBLE RUNS) CONTINUE TO  
SHOW A SOLUTION CLOSER TO THAT OF THE ECMWF, SUGGESTING THE GFS  
REMAINS AN OUTLIER. THIS THEN TIES INTO HOW A SURFACE LOW LIFTS  
OUT OF THE ITCZ LATE THURSDAY INTO FRIDAY AND HOW MUCH QPF MOVES  
ACROSS THE ISLANDS IN RESPONSE TO THIS SURFACE LOW AND FRONT.  
AGAIN, THE PREVIOUS RUNS OF THE GFS ARE MUCH FARTHER EAST WITH THE  
SURFACE LOW (WITH THE 00Z EAST OF THE BIG ISLAND) WHICH IN TURN  
RESULTS IN LESS OVERALL QPF THAN MOST OTHER MODELS.  
 
DESPITE THE FAIRLY SIGNIFICANT DIFFERENCES IN THE DETAILS, ALL  
MODELS DO SUGGEST A WET PATTERN FOR ALL OF THE HAWAIIAN ISLANDS BY  
LATER IN THE WEEK. AS EXPECTED, CONFIDENCE IN THOSE DETAILS AND  
HOW MUCH RAINFALL DOES FALL, IS STILL FAIRLY LOW AT THIS POINT.  
 
SANTORELLI  
 

 
 
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