Secular Variation in Atlantic Coast Extratropical Cyclones

Abstract

To define spatial and temporal variations in annual cyclone frequencies, principal components were calculated from a matrix of annual frequencies for 74 grid cells covering eastern North America and the western North Atlantic and the years 1885 to 1978. The first principal component contrasts cyclone frequencies in continental versus marine areas. Since the early years of this century, there has been a trend toward increased cyclone frequency over marine areas and a decline in frequencies over the continent. This trend peaked in the 1960's. The second principal component is interpreted as an east coast cyclogenesis function. Like the first component, it exhibits a century-long secular variation with increasing coastal cyclogenesis in recent decades and a maximum in the 1950's. The first two components explain 45% of the oral variance. Higher order vectors (3rd and 4th) explained 12% of the variance and geographically depict variance in the Gulf coast and Great Lakes regions, respectively. Secular variations in the weightings of the third and fourth components contain higher frequency variations than the first and second components.