Changes in Number and Intensity of World-wide Tropical Cyclones

Bayesian statistical models were developed for the number of tropical cyclones and the rate at which these cyclones became hurricanes in the North Atlantic, North and South Indian, and East and West Pacific Oceans. We find that there is small probability that the number of cyclones has increased in the past thirty years. The rate at which these storms become hurricanes appears to be constant. The rate at which hurricanes evolve into category 4 and higher major storms does appear to have increased. We also investigate storm intensity by measuring the distribution of individual storm lifetime in days, storm track length, and Emanuel’s power dissiptation index. We find little evidence that, overall, the mean of the distribution of individual storm intensity is changing through time, but the variability of the distribution has increased. The cold tongue index and the North Atlantic oscillation index were found to be strongly associated with storm quality in the Western, and to a smaller extent, the Eastern Pacific oceans. The North Atlantic oscillation index was strongly associated with the increase in the rate of strong storms evolving.