The distribution of annual tropical cyclone frequency

In preparation for studying and fitting tropical cyclone frequency distributions certain time trends in the climatological series are tested statistically and explanations of their possible cause proposed. The annual frequency of tropical cyclones and hurricanes is hypothesized to be a rare-event type of series. On the basis of physical and statistical principles it is shown how the Poisson and negative binomial distributions are adapted to fitting the climatological series under prescribed physical conditions. These distributions are shown to provide good statistical fits and therefore good estimates of probabilities of annual cyclone frequency. Where necessary, the effects of trend are removed and corresponding adjustments made in the distribution parameters.