484  
FXHW01 KWNH 261225  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
824 AM EDT THU OCT 26 2017  
 
VALID 00Z FRI OCT 27 2017 - 00Z FRI NOV 03 2017  
 
AT THE START OF THE PERIOD, A SHORTWAVE TROUGH TO THE NORTH WAS  
SEEN EXITING THE REGION WITH FRONTAL SHOWERS GRADUALLY COMING TO  
AN END ACROSS THE BIG ISLAND. WHILE THE SYSTEM DOES CUT OFF  
GENERALLY BETWEEN 150-140W LONGITUDE, IT SHOULD REMAIN FAR ENOUGH  
TO KEEP PRIMARY IMPACTS AWAY FROM HAWAI`I. THE 00Z UKMET WAS A  
NOTABLE OUTLIER BEING DECIDEDLY WEST OF THE CONSENSUS. EVENTUALLY  
A MUCH STRONGER BAND OF HEIGHT FALLS CROSS THE INTERNATIONAL  
DATELINE THIS WEEKEND WITH THE RESULTANT CLOSED LOW OFF TO THE  
NORTHWEST OF THE STATE BY TUESDAY. THE GUIDANCE VARY CONSIDERABLY  
WITH THIS FEATURE AS THE 06Z GFS SPED UP WELL AHEAD OF THE 00Z RUN  
WHICH WAS ON THE FAR WESTERN SIDE OF THE SPREAD. CURRENTLY, THE  
06Z GFS ONLY HAS THE 00Z CMC AS A COMPARABLE SOLUTION. ENSEMBLE  
SPAGHETTI PLOTS ARE SCATTERED ACROSS THE BOARD SUGGESTING A BELOW  
AVERAGE CONFIDENCE FORECAST IN PLAY MOVING INTO NEXT WEEK. GIVEN  
THE SYSTEM DOES CLOSE OFF, WOULD PREFER TO STAY ON THE SLOWER SIDE  
OF THE ENVELOPE WHICH SUGGESTS THE 06Z GFS IS TOO QUICK.  
 
IN THE WAKE OF A SHEARING FRONTAL ZONE, LIGHT NORTH-NORTHWESTERLY  
FLOW IS NOTED ALTHOUGH SOME RESIDUAL HIGH PRECIPITABLE WATER AIR  
LINGERS OVER THE BIG ISLAND WHICH KEEPS SCATTERED SHOWERS IN THE  
FORECAST. MODELS SHOWS A WEAK SHEAR AXIS REMAINS OVER THE SOUTHERN  
MOST ISLANDS INTO THE WEEKEND. BY EARLY NEXT WEEK, LIGHT WARM  
ADVECTION STARTS TO TAKE SHAPE WITH 5 TO 10 KNOT  
SOUTH-SOUTHEASTERLY FLOW ENSUING OVER MUCH OF THE REGION. A  
RESULTANT INCREASE IN MOISTURE WILL ENHANCE THE COVERAGE OF SHOWER  
ACTIVITY INTO EARLY NEXT WEEK AS A COLD FRONT APPROACHES FROM THE  
NORTHWEST. THE 00Z ECMWF DOES SHOW THE BOUNDARY REACHING KAUAI BY  
THE MIDDLE OF NEXT WEEK WHICH WOULD BRING MORE ORGANIZED RAINFALL  
TO THE REGION. HOWEVER, TOO MUCH UNCERTAINTY EXISTS AT THIS TIME  
GIVEN THE MYRIAD OF FRONTAL PLACEMENTS NOTED.  
 
RUBIN-OSTER  
 

 
 
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