Recent Secular Variations in Mid-Atlantic Winter Extratropical Storm Climate

Abstract

An increase in storm damage along the east coast of the United States coincides with secular variations of the general circulation documented by several recent investigations. To determine the coupling between large-scale circulation patterns and extratropical storms along the mid-Atlantic coast, a principal-component analysis is used to characterize patterns of 5-day mean surface pressure and, within objective categories of these patterns, conditional probabilities of storm occurrences are calculated. Based on this probabilistic coupling, secular variations in frequencies of surface pressure patterns are used to estimate secular variations in mid-Atlantic storm climate. The results suggest that a significant trend has occurred in large-scale circulation. Physical interpretation of this change suggests an increase in the frequency of high-latitude blocking. Associated recent secular changes in storm climate are 1) an offshore displacement of the mean storm track; 2) an increase in the number of storms moving offshore; and 3) a tendency toward two modes, rather than one, of storm tracks along the mid-Atlantic coast. Since such changes alter the frequency of extreme wave and surge conditions along the coast, the consequences are highly significant in terms of human impact.