474 
 WTPA41 PHFO 280254
 TCDCP1
 
 TROPICAL STORM NIALA DISCUSSION NUMBER  13
 NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI   CP062015
 500 PM HST SUN SEP 27 2015
  
 NIALA IS NOW DEVOID OF DEEP CONVECTION...AND HAS BEEN SINCE ABOUT 
 2200 UTC. THE WELL-DEFINED LOW CLOUD SWIRL KEEPS FIX CONFIDENCE HIGH 
 THIS AFTERNOON. SUBJECTIVE DVORAK SATELLITE INTENSITY ESTIMATES 
 REFLECT THIS WORSENING SATELLITE PRESENTATION...WITH 2.5...35 
 KT...GIVEN BY ALL THREE SATELLITE CENTERS. UW-CIMSS ADT WAS 2.7...39 
 KT. HOWEVER...A 1935 UTC ASCAT PASS SHOWED A 50 NM WIDE SWATH OF 40 
 KT WINDS ACROSS THE NORTHERN SEMICIRCLE. SOME TIME HAS PASSED SINCE 
 THEN...BUT WE WILL DROP THE INITIAL INTENSITY TO A POSSIBLY GENEROUS 
 40 KT...INSTEAD OF 35 KT...IN A NOD TO THAT ASCAT PASS.
  
 INITIAL MOTION IS 250/08 KT...REPRESENTING A NOTICEABLE INCREASE IN
 FORWARD SPEED SINCE THIS MORNING. A WEAKENING NIALA CONTINUES TO BE
 STEERED BY STRONG HIGH PRESSURE FAR NORTH OF THE MAIN HAWAIIAN
 ISLANDS...SO IT SHOULD BE EXPECTED THAT SYSTEM MOTION WOULD SLOWLY
 APPROACH BACKGROUND LOW LEVEL ENVIRONMENTAL FLOW. TRACK GUIDANCE 
 SHOWS THIS...REMAINING TIGHTLY CLUSTERED AND TAKING NIALA TOWARDS 
 THE WEST SOUTHWEST TO SOUTHWEST THROUGH FIVE DAYS. THE CURRENT 
 FORECAST TRACK CLOSELY FOLLOWS THE LAST ONE...WITH FASTER MOVEMENT 
 THROUGH 36 HOURS FOLLOWED BY SLOWER MOTION AFTERWARDS AS PER 
 CONSENSUS MODELS. 
 
 SHEAR ACROSS NIALA IS ANALYZED AT 32 KT FROM SHIPS AND 43 KT FROM
 UW-CIMSS THIS AFTERNOON...SO IT IS NOT SURPRISING THAT NIALA IS
 WEAKENING EVEN AS IT PASSES OVER INCREASINGLY WARM WATER. INTENSITY
 GUIDANCE UNANIMOUSLY WEAKENS NIALA...BUT AT VARIOUS RATES. ECMWF
 AND ICON COMPLETELY DISSIPATE THIS SYSTEM AFTER 48 AND 72
 HOURS...RESPECTIVELY...WHILE MODELS LIKE GFS AND HWRF KEEP NIALA
 ALIVE AS A REMNANT LOW THROUGH 120 HOURS. OUR FORECAST WEAKENS
 NIALA TO A DEPRESSION AT 24 HOURS...THEN TO A POST-TROPICAL/REMNANT
 LOW AT 48 HOURS. HOWEVER...LIKE THE LAST FEW FORECAST CYCLES...WE DO
 NOT DISSIPATE THIS SYSTEM COMPLETELY. LONG RANGE GLOBAL MODELS
 DEPICT UNSPECIFIED TROPICAL DEVELOPMENT IN THE GENERAL AREA
 SOUTHWEST OF THE HAWAIIAN ISLANDS WHERE ANY REMNANTS OF NIALA WOULD
 LINGER IN SEVEN TO TEN DAYS.
 
 THERE ARE NO WATCHES...WARNINGS OR ADVISORIES ASSOCIATED WITH
 NIALA...BUT THERE CONTINUE TO BE REAL HAZARDS ACROSS PORTIONS OF
 THE MAIN HAWAIIAN ISLANDS RELATED TO MOISTURE AND SWELL BROUGHT
 IN BY STRONG TRADE WINDS...ALONG WITH THE DIMINISHING RESIDUAL NIALA
 SWELL MAINLY TO THE BIG ISLAND. THESE WINDS ARE DRIVEN BY THE HIGH
 FAR NORTH OF THE MAIN HAWAIIAN ISLANDS...THE SAME HIGH PUSHING NIALA
 ALONG. THE HONOLULU WFO CONTINUES TO ISSUE FLOOD WATCH AND HIGH SURF
 ADVISORY PRODUCTS...ALONG WITH PRODUCTS DESCRIBING MARINE AND
 AVIATION HAZARDS...RELATED TO THIS STRONG TRADE WIND FLOW. 
  
  
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  28/0300Z 15.7N 155.5W   40 KT  45 MPH
  12H  28/1200Z 15.4N 156.7W   35 KT  40 MPH
  24H  29/0000Z 15.1N 158.3W   30 KT  35 MPH
  36H  29/1200Z 14.8N 159.7W   30 KT  35 MPH
  48H  30/0000Z 14.4N 161.1W   25 KT  30 MPH...POST-TROP/REMNT LOW
  72H  01/0000Z 13.7N 163.3W   25 KT  30 MPH...POST-TROP/REMNT LOW
  96H  02/0000Z 13.1N 165.2W   25 KT  30 MPH...POST-TROP/REMNT LOW
 120H  03/0000Z 12.6N 166.7W   25 KT  30 MPH...POST-TROP/REMNT LOW
  
 $$
 FORECASTER POWELL