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Water Temperature and Cyclone Frequency in the Pacific: Implications for Pearl Farming Final, June 2008Niña events. Basher and Zheng (1995) noted that cyclones were more common at latitudesgreater than 19º S during La Niña events, but most common between latitudes 12º S and 23ºS during strong El Niño events. They also estimated that the risk to the Southwest Pacificregion as a whole was 28% greater than average during El Niño events.NIWA (1997) estimated the annual chance of a cyclone occurring within 100 km 2 of the mainisland groups based on data averaged across the period 1969/1970 and 1988/1989. The riskwas estimated to be 60%, 50%, 30%, 15% and 10% for Vanuatu, Fiji, Southern Cook Islands,French Polynesia and the Solomon islands, respectively. During strong El Niño events, theyindicated that the risk of cyclones increased to 75% for the Southern Cook Islands and 50%for French Polynesia, but remained at 50% for Fiji, declined to 40% for Vanuatu and wasconsidered negligible for the Solomon Islands. The average number of tropical cyclones peryear passing within 550 km (5°) of the major island groups in the South Pacific has also beenestimated (Salinger et al. 2007). The estimates are 3.0 for Vanuatu, 2.3 for Fiji, 1.5 for thesouthern Cook Islands, 1.3 for the Solomon Islands, 0.8 for the Northern Cook Islands, 0.8-0.1 for the major archipelagos in French Polynesia, and 0.6 for Papua New Guinea. Theyalso point out that on average about four cyclones per season have wind speeds in excess of118 km/h (category 4) and two of these usually reach category 5 status with mean windspeeds greater than 167 km/h.The total number of tropical cyclones that passed within 50, 100 and 200 km of variouslocations within the specified regions between1969/1970 and 2004/2005 was estimated byexamining the tracks in the southern hemisphere tropical cyclone archive compiled by theNational Climate Centre, Bureau of Meteorology, Australia (Bureau of Meteorology 2007c)(Table 1). During this period, fewer tropical cyclones passed within 50 km and 100 km ofBroome and Exmouth on the north-west Australian coast than most of the locations inVanuatu and some of those in Fiji. More tropical cyclones passed within 200 km of theVanuatu coast, than both the Fijian and north-west Australian coast. Table 1 also suggeststhat the risk of a tropical cyclone passing varies within individual countries. In Fiji, forexample, seven tropical cyclones passed within 50 km of Viwa, but only one passed nearLakeba, Matuku and Suva. Likewise in Vanuatu, nine tropical cyclones passed within 50 kmof Aneityum, Lamap, Port Vila and Sola, but only five did so near Pekoa Airport.The north-west coast of Australia between Exmouth Gulf and Broome has the highestincidence of tropical cyclones in the southern hemisphere (Bureau of Meteorology, 2008).This region is also the most prone to severe tropical cyclones. About five tropical cyclones,on average, form each season over the warm ocean waters off the northwest coast betweenlongitudes 105°E and 125°E. Only two of these usually cross the coast and only one of theseis severe. Broome has experienced 22 tropical cyclones since 1910. This is equivalent toabout one every four years, however, the frequency has declined in recent decades, withonly two cyclones occurring between 1990 and 2004 (Bureau of Meteorology 2007d). In theExmouth area, tropical cyclones with wind gusts greater than 90 km/h occur about onceevery two to three years on average, but only three gale-causing cyclones have occurredsince 1982 (Bureau of Meteorology 2007e). In the Northern Territory, there are on average7.7 days of cyclone activity per season (Bureau of Meteorology 2007f). The Gulf ofCarpentaria usually averages two cyclones a year, while the Arafura and Timor Seasaverage one per year. On the east coast of Australia, there are on average 4.7 tropicalcyclones per year.The Ecology Lab Pty Ltd – Marine and Freshwater Studies Page 13