Historical Tropical Cyclone Activity and Impacts in the Cook Islands.

Abstract

Analysis of a recently completed database of 143 tropical cyclones in the Cook Islands revealed a minimum average frequency of 0.8 cyclones per cyclone season between 1820 and 2006, with a more-precise frequency of 1.8 cyclones per season with the beginning of satellite monitoring of cyclones in 1970. Since 1970, 31% of cyclones have reached hurricane intensity. The Southern Cooks have been more than twice as frequently affected by cyclones as the Northern Cooks, with the island of Palmerston having the greatest number of encounters. Since 1820, 96% of cyclones have occurred during the official November–April cyclone season, with February alone accounting for 29%. Since 1970, 46% of cyclones achieving hurricane status have occurred in February. Nevertheless, Cyclone Martin in October–November 1997 demonstrated the dangers of a cyclone occurring outside the official season. An increase in cyclone occurrences since the mid-1970s is probably attributable to satellite monitoring, but it is noteworthy that all six cyclones known for certain to have achieved major hurricane status have occurred since 2002. Since 1970, 56% of cyclones have occurred during El Nino events, an increase of 15% from the 1870–1969 period. Since 1891, cyclones with moderate and major human impacts have occurred on average at least every 3.8 and 8.8 yr, respectively, with the Southern Cooks more than twice as frequently affected as the Northern Cooks. However, past cyclone disasters in the latter group suggest that risk to human life is greater there due to the potential for inundation of the atolls by storm surges. Half of cyclones with human impacts have occurred during El Nino events, with weak to moderate El Ninos almost as important in this respect as strong El Ninos. Only 13% of cyclone impacts have occurred during La Nina events.