936  
FXHW01 KWNH 271224  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
824 AM EDT FRI OCT 27 2017  
 
VALID 00Z SAT OCT 28 2017 - 00Z SAT NOV 04 2017  
 
AS A MID-LATITUDE UPPER LOW SLOWLY DRIFTS EASTWARD AWAY FROM THE  
HAWAI`IAN ISLAND CHAIN, SHORTWAVE RIDGING WILL SET UP FOR THE  
WEEKEND. LOOKING TOWARD THE INTERNATIONAL DATELINE, A BROAD BAND  
OF HEIGHT FALLS BEGIN TO TAKE SHAPE WITHIN THE ACTIVE MID-LATITUDE  
FLOW REGIME. ALL SIGNS POINT TOWARD THE SYSTEM CLOSING OFF,  
GENERALLY ALONG 170W WHICH SEEMS TO BE A SLOWING TREND RELATIVE TO  
THE SPREAD NOTED YESTERDAY. EVENTUALLY A NORTHWARD JOG IS NOTED AS  
THE CIRCULATION BECOMES ABSORBED INTO A BROAD NEGATIVE HEIGHT  
ANOMALY ACROSS THE NORTHERN PACIFIC. THIS WILL ULTIMATELY ALLOW  
HEIGHTS TO RISE OVER HAWAI'I WITH THE 00Z CMC EVEN SHOWING A  
588-DM CLOSED HIGH FORMING BY THURSDAY. THIS OVERALL SHIFT IN THE  
GUIDANCE IS MUCH MORE CONSISTENT AMONG THE ENSEMBLE MEMBERS  
ALTHOUGH SOME SPATIAL SPREAD DOES PERSIST LATER IN THE PERIOD.  
 
IN THE WAKE OF A SHEARING FRONTAL ZONE, LIGHT NORTHERLY FLOW WILL  
CONTINUE OVER THE ISLANDS WHILE A MORE EASTERLY COMPONENT IS NOTED  
TOWARD THE END OF THE WEEKEND. LOOKING AHEAD TO MONDAY AND PERIODS  
ONWARD, WARM ADVECTION WILL ENSUE AHEAD OF THE NEXT LONGWAVE  
TROUGH WHICH ULTIMATELY FAVORS GENERAL SOUTH-SOUTHEASTERLY FLOW.  
BY TUESDAY, SOME INTENSIFICATION IN THE WIND FIELD IS EXPECTED  
GIVEN THE STRENGTHENING OF THE SURFACE GRADIENTS. AS THE UPSTREAM  
TROUGH LIFTS TOWARD THE NORTH-CENTRAL PACIFIC, A RETURN TO THE  
MORE CLIMATOLOGICAL TRADE WIND REGIME IS IN THE FORECAST FROM  
WEDNESDAY ONWARD. IN TERMS OF PRECIPITATION THREATS, SCATTERED  
SHOWERS ARE EXPECTED IN THE WAKE OF THE DISSIPATING FRONTAL ZONE  
ALTHOUGH OVERALL MOISTURE CONTENT IS ON THE LOWER SIDE. WARM  
ADVECTION WILL EVENTUALLY BRING HIGH PRECIPITABLE WATER AIR FROM  
THE TROPICS TOWARD HAWAI`I BY MONDAY/TUESDAY WHICH MAY ENHANCE THE  
COVERAGE OF SHOWER ACTIVITY. EVENTUALLY THE UPSTREAM FRONTAL ZONE  
MAY APPROACH THE ISLAND OF KAUAI BY MID-WEEK BEFORE THE BOUNDARY  
LIFTS NORTHWARD BY THE FOLLOWING DAYS. DEPENDING ON ITS ULTIMATE  
POSITION, SOME HEAVY RAINFALL THREAT MAY AFFECT KAUAI BUT IT COULD  
EASILY STAY OFF TOWARD THE NORTHWEST.  
 
RUBIN-OSTER  
 

 
 
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