TROPICAL CYCLONE OCCURRENCES IN THE VICINITY OF HAWAII - ARE THE DIFFERENCES BETWEEN EL-NINO AND NON-EL NINO YEARS SIGNIFICANT

Tropical cyclones in the vicinity of Hawaii are rare. However, when th ey occurred, they caused enormous property damage. The authors have ex amined historical records (1949-95) of cyclones and classified them in to El Nino and non-El Nino batches. A bootstrap resampling method is u sed to simulate sampling distributions of the annual mean number of tr opical cyclones for the above two batches individually. The statistica l characteristics for the non-El Nino batch are very different from th e El Nino batch. A two-sample permutation procedure is then applied to conduct statistical tests. Results from the hypothesis testing indica te that the difference in the annual mean number of cyclones between E l Nino and non-El Nino batches is statistically significant at the 5% level. Therefore, one may say with statistical confidence that the mea n number of cyclones in the vicinity of Hawaii during an El Nino year is higher than that during a non-El Nino year. Likewise, the differenc e in variances between El Nino and non-El Nino batches is also signifi cant. Cyclone tracks passing Hawaii during the El Nino batch appear to be different from those of the non-El Nino composite. A change in lar ge-scale dynamic and thermodynamic environments is believed to be cond ucive to the increased cyclone incidence in the vicinity of Hawaii dur ing an El Nino year.