598  
FXHW01 KWNH 271231  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
730 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 HEAVY RAINFALL INTO THE NORTHWESTWARD MOST ISLANDS  
AS WELL 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) WHILE THE ECMWF  
AND ENSEMBLES ARE WELL WEST, JUST WEST OR SOUTH OF THE ENTIRE  
ISLAND CHAIN.  
 
00Z GEFS M-CLIMATE QPF PERCENTILES REMAIN AT OR ABOVE THE 99TH  
PERCENTILE (SOME MAX VALUES AS WELL) FROM ABOUT THURSDAY ONWARD SO  
THE POTENTIAL REMAINS FOR MODEST TO LOCALLY HEAVY RAIN NEXT WEEK,  
PERHAPS SHIFTING FROM THE SOUTHEASTERN ISLANDS TO THE WESTERN  
ISLANDS AS THE PATTERN EVOLVES AND ASSUMING A SURFACE LOW LIFTS  
NORTHWARD TO THE WEST OF THE REGION.  
 
SANTORELLI  
 

 
 
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