136  
FXHW01 KWNH 011231  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
730 AM EST FRI DEC 01 2017  
 
VALID 00Z SAT DEC 02 2017 - 00Z SAT DEC 09 2017  
   
..A HEAVY PRECIPITATION THREAT EARLY IN THE PERIOD
 
 
INITIALLY, A LONGWAVE TROUGH WILL PASS TO THE EAST OF THE  
HAWAI`IAN ISLAND CHAIN WHILE THE TAIL END OF THE HEIGHT FALLS  
SHOULD LINGER OVER THE REGION THIS WEEKEND. THE ELONGATED BAND OF  
VORTICITY IS FORECAST TO DRIFT SOUTHWARD IN TIME TOWARD THE  
EQUATORIAL PACIFIC BY EARLY NEXT WEEK. EVENTUALLY ANOTHER POTENT  
SYSTEM WILL SWING SOUTHWARD OUT OF THE MID-LATITUDES WITH  
ADDITIONAL SHORTWAVE ENERGY FOLLOWING IN ITS WINGS. WHILE THE  
STRONGEST FORCING SHOULD STAY WELL NORTHEAST OF HAWAI`I, A  
LINGERING BATCH OF HEIGHT FALLS SHOULD SWING THROUGH THE REGION BY  
MID-WEEK. WHILE THE GLOBAL GUIDANCE IS IN AGREEMENT WITH THE  
OVERALL FORECAST EVOLUTION THE NEXT WEEK, THEY VARY WITH THE  
DETAILS, PARTICULARLY THE 00Z ECMWF WHICH SHOWS A CUT-OFF UPPER  
LOW LOOMING SOUTHEAST OF THE STATE BY LATE NEXT WEEK.  
 
AT THE SURFACE, STRONG RIDGING TO THE NORTH WILL ENCOURAGE A  
STEADY PERIOD OF MODERATE TRADE WINDS, APPROACHING THE 20 TO 25  
KNOT RANGE AT TIMES. THIS FLOW REGIME SHOULD CONTINUE INTO THE  
WEEKEND WITH A GRADUAL SLACKENING OF THE WIND FIELDS. BY MONDAY, A  
DEEPENING CYCLONE TO THE NORTH AND EAST SHOULD SUPPORT A  
STRENGTHENING COLD ADVECTION PATTERN AS MODERATE TO OCCASIONALLY  
STRONG NORTHERLY FLOW ENSUES. THIS WILL ULTIMATELY SHUNT A GREAT  
DEAL OF THE TROPICAL MOISTURE EQUATORWARD. BY THE MIDDLE OF NEXT  
WEEK, A WEAKENING PRESSURE GRADIENT WILL EVENTUALLY DECREASE THE  
STRENGTH OF THE NORTHERLIES WITH LIGHTER WINDS EXPECTED FOR THE  
REMAINDER OF THE PERIOD. REGARDING PRECIPITATION THREATS, LOCALLY  
HEAVY RAINFALL WILL BE POSSIBLE DURING THE NEXT 24 HOURS AS A HIGH  
PRECIPITABLE WATER ENVIRONMENT REMAINS IN PLACE. BY LATER IN THE  
WEEKEND, DRIER AIR WILL WORK ITS WAY INTO THE REGION WHICH SHOULD  
DECREASE THE COVERAGE OF SHOWER ACTIVITY. THE NEXT FRONTAL SURGE  
SHOULD BRING ANOTHER THREAT FOR SHOWERS BY TUESDAY/WEDNESDAY  
ALTHOUGH THIS SHOULD BE BRIEF GIVEN THE QUICK PROGRESSION OF THE  
FRONTAL BOUNDARY.  
 
RUBIN-OSTER  
 

 
 
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