Hurricane Clusters in the Vicinity of Florida

Models that predict annual U.S. hurricane activity assume a Poisson distribution for the counts. Here the authors show that this assumption applied to Florida hurricanes leads to a forecast that underpredicts both the number of years without hurricanes and thenumber of years withthree or more hurricanes. Theunderdispersion in forecast counts arises from a tendency for hurricanes to arrive in groups along this part of the coastline. The authors then developan extension totheirearlier statistical model that assumes that the rateofhurricane clusters follows a Poissondistribution with cluster size capped at two hurricanes. Hindcastsfromthe cluster model better fit the distribution of Florida hurricanes conditional on the climate covariates including the North Atlantic Oscillation and Southern Oscillation index. Results are similar to models that parameterize the extra-Poisson variation in the observed counts, including the negative binomial and the Poisson inverse Gaussian models. The authors argue, however, that the cluster model is physically consistent with the way Florida hurricanes tend to arrive in groups.