Trends in the Frequencies of Cyclone Activity over North America

Abstract

Trends in cyclone frequencies over North America were determined for the period 1949–76 for four mid-season months. The general trend has been for a decrease in the number of cyclonic events, but with fluctuations. There is a tendency for the trends in frequency to be associated with trends in the mean temperature of the Northern Hemisphere and latitudinal temperature gradients as reported in the literature.