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 077 
 WTPA41 PHFO 270249
 TCDCP1
 
 TROPICAL STORM NIALA DISCUSSION NUMBER   9
 NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI   CP062015
 500 PM HST SAT SEP 26 2015
  
 SINCE THE LOW LEVEL CIRCULATION CENTER...LLCC...BECAME EXPOSED THIS
 MORNING...THE MYSTERY CONCERNING THE LOCATION OF NIALA HAS BEEN
 REMOVED. A SECOND BURST OF DEEP CONVECTION JUST NORTHEAST OF THE
 LLCC HAS BEGUN TO SUBSIDE...LEAVING A WELL-DEFINED LOW CLOUD SWIRL.
 OVERALL PRESENTATION CONTINUES TO BE OF A SYSTEM UNDERGOING
 DEBILITATING WEST SOUTHWEST SHEAR...WITH THE ONLY OUTFLOW CHANNEL
 CONTINUING TO BE TOWARDS THE NORTHEAST. UW-CIMSS NOW ANALYZES 40 KT
 OF SHEAR...WHILE SHIPS SHOWS 25 KT. NEITHER VALUE IS HEALTHY FOR A
 TROPICAL CYCLONE. SUBJECTIVE DVORAK SATELLITE INTENSITY ESTIMATES
 RANGE FROM 3.5...55 KT...FROM SAB AND PHFO...TO 3.0...45 KT...FROM
 JTWC. UW-CIMSS ESTIMATES NIALA INTENSITY IS 50 KT. BETWEEN 2300 UTC
 AND 0000 UTC...NIALA PASSED ABOUT 40 NM SOUTH OF BUOY FOUR...WHICH
 REPORTED A PEAK WIND OF 47 KT BETWEEN THOSE HOURS. GIVEN THIS
 STRENGTH AND DISTANCE FROM THE LLCC...AND IN AGREEMENT WITH TWO OF
 THE THREE SATELLITE CENTERS...WE WILL KEEP NIALA AT 55 KT FOR THIS
 ADVISORY. 
 
 INITIAL MOTION IS 270/07 KT. SINCE MOST ASSOCIATED DEEP CONVECTION
 IS GONE...PRIMARY STEERING FOR NIALA WILL BE PROVIDED BY THE STRONG
 HIGH PRESSURE CENTER FAR NORTH OF HAWAII. THIS HIGH IS ALREADY
 DRIVING NEAR-GALE FORCE EAST NORTHEAST TRADE WINDS ACROSS PORTIONS
 OF THE ALOHA STATE AND SURROUNDING WATERS...AND WILL LIKELY FORCE
 NIALA TO ASSUME A WEST SOUTHWEST MOTION WITHIN 48 HOURS. THE
 CURRENT FORECAST TRACK CLOSELY FOLLOWS THE PREVIOUS ONE...KEEPING
 NIALA MOVING WESTWARD THROUGH SUNDAY...THEN CURVING ITS TRACK
 GENTLY WEST SOUTHWESTWARD WITHIN PREVAILING LOW LEVEL FLOW
 AFTERWARDS. FORWARD MOTION HAS BEEN INCREASED SLIGHTLY THROUGH DAY
 FIVE...IN KEEPING WITH CONSENSUS TRACK GUIDANCE...MOVING UP THE
 TIME OF CLOSEST APPROACH TO THE BIG ISLAND TO SUNDAY AFTERNOON
 VERSUS SUNDAY EVENING. WITH NIALA NOT EXPECTED TO
 REINTENSIFY...THERE IS SIMPLY NOTHING TO SLOW NIALA DOWN AS IT
 WEAKENS. ALTHOUGH THE TROPICAL STORM WATCH FOR THE BIG ISLAND WILL
 REMAIN IN PLACE THROUGH THIS CYCLE...THE ONSET AND CUMULATIVE
 PROBABILITIES FOR TROPICAL STORM FORCE WINDS THERE HAVE
 DECREASED...THANKS TO A COMBINATION OF WESTERLY SYSTEM MOTION AND A
 PAIR OF INITIAL FORECAST POINTS FARTHER SOUTH THAN ANTICIPATED WHEN
 THE WATCH WAS INITIALLY ISSUED. IT MAY BE POSSIBLE TO CANCEL THE
 WATCH LATER TONIGHT IF CURRENT TRENDS HOLD.
 
 INTENSITY GUIDANCE ALMOST UNANIMOUSLY WEAKENS NIALA THROUGH FIVE
 DAYS...WITH ICON AND SHIPS DISSIPATING THIS SYSTEM COMPLETELY AFTER
 48 HOURS. IN CONTRAST...GLOBAL MODELS KEEP NIALA ALIVE AT TROPICAL
 STORM STRENGTH THROUGH THE FORECAST PERIOD. OUR FORECAST OF GRADUAL
 WEAKENING IS A BLEND OF THESE TRENDS...REDUCING NIALA TO A
 POST TROPICAL/REMNANT LOW ON DAY FOUR...BUT NOT DISSIPATING IT
 COMPLETELY. 
 
 
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  27/0300Z 16.9N 152.8W   55 KT  65 MPH
  12H  27/1200Z 16.9N 153.9W   50 KT  60 MPH
  24H  28/0000Z 16.7N 155.3W   45 KT  50 MPH
  36H  28/1200Z 16.3N 156.6W   40 KT  45 MPH
  48H  29/0000Z 15.9N 158.0W   35 KT  40 MPH
  72H  30/0000Z 15.1N 160.6W   30 KT  35 MPH
  96H  01/0000Z 14.4N 163.2W   25 KT  30 MPH...POST-TROP/REMNT LOW
 120H  02/0000Z 14.0N 166.2W   25 KT  30 MPH...POST-TROP/REMNT LOW
  
 $$
 FORECASTER POWELL
 
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