  Bayesian statistical models were developed for the number of tropical
cyclones and the rate at which these cyclones became hurricanes in the North
Atlantic. We find that, controlling for the cold tongue index and the North
Atlantic oscillation index, there is high probability that the number of
cyclones has increased in the past thirty years; but the rate at which these
storms become hurricanes appears to be constant. 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 the distribution of individual storm intensity is changing
through time. Any increase in cumulative yearly storm intensity and potential
destructiveness, therefore, is due to the increasing number of storms and not
due to any increase in the intensity of individual storms.
