INBOUND DSNDING DC9 ON VISUAL APCH HAS NMAC WITH A CESSNA WHO WAS SUPPOSED TO BE OVER THE SHORELINE. OVERWATER OP. NON RADAR APCH PROC.

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WHILE ON A VISUAL APCH TO KOA APPROX 12 NM NW OF THE KOA ARPT ON THE KONA VORTAC 330 DEG RADIAL; WE RECEIVED A TCASII TA INDICATING TFC BELOW US WHILE DSNDING THROUGH 4000 FT MSL. (WE HAD PREVIOUSLY SLOWED OUR DSCNT AND AIRSPD TO ACCOMMODATE A LAGGING CABIN ALT.) THERE HAD BEEN NO PRIOR DISPLAY OF A TFC SYMBOL ON THE TCASII. IN A MATTER OF A FEW SECONDS THE TCASII WENT FROM A TA WITH TFC 600 FT BELOW US TO A FULL RA WITH INSTRUCTIONS TO 'CLB.' WE ARRESTED THE DSCNT AND INITIATED A CLB; HOWEVER; TCASII SEPARATION HAD CLOSED TO WITHIN 200 FT BEFORE THE VERT FLT PATH OF OUR ACFT COULD BE REVERSED. AT NO TIME DID WE HAVE VISUAL CONTACT WITH THE CONFLICTING ACFT. WE CLBED TO APPROX 4600 FT MSL TO CLR THE RA. WE HAD NOT BEEN ADVISED OF ANY TFC IN THE AREA BY THE RESPECTIVE CTLRS; EITHER PRIOR TO HDOF BY ZHN OR AFTER HDOF TO THE KOA TWR. WHEN QUESTIONED BY US AFTER LNDG; THE KOA TWR CTLR STATED THAT THE TFC CESSNA HAD PREVIOUSLY BEEN INSTRUCTED TO REMAIN ON THE SHORELINE AND THAT SHE BELIEVED THE TFC WAS IN THE VICINITY OF THE KONA VILLAGE HOTEL; AS INSTRUCTED; DURING OUR VISUAL APCH. THE KOA TWR CTLR ALSO STATED THAT SHE DID NOT HAVE THE CONFLICTING TFC IN SIGHT DURING THE INCIDENT. IN FACT; THE CESSNA WAS WELL OUT TO SEA AT OUR POS NW OF THE KOA ARPT PLACING IT ON THE USUAL ARR PATH OF THE APCHING ACR TFC LNDG ON RWY 17. WX CONDITIONS WERE EXCELLENT WITH VISIBILITY AT LEAST 20 MI; ONLY HIGH CLOUD COVER AND NO HAZE.