Hurricane Climatic Fluctuations. Part I: Patterns and Cycles

Abstract

Hurricane records for 1899 through 1978 are used to determine the numbers of hurricanes during the period August through October of each year that were present in the Atlantic. The Atlantic basin is subdivided into four geographic regions: the Central Atlantic, East Coast, Gulf of Mexico and Caribbean. An empirical orthogonal function (EOF) analysis is made of the time series of hurricane occurrence in each region to derive the dominant uncorrelated modes of interannual variability of seasonal hurricane incidence. The first EOF mode, accounting for 68% of the variance, represents the overall activity of the hurricane season. The second mode, accounting for 16% of the variance, represents the shift of hurricane incidence between the Gulf plus Caribbean, and the East Coast regions. A coherency spectrum between the time variations of the first and second modes indicates a significant coherence at periods of about 2.5 and 4.5 years. The coherence at 2.5 years corresponds to the quasi-biennial oscillation (QBO). The results are related to the QBO in monthly hurricane numbers and in the strength and position of the North Atlantic subtropical high found by Angell et al. (1969). It is found that the maximum in East Coast hurricane incidence occurs at the phase of the QBO when the subtropical high is at its farthest northeastern displacement. The relation of the coherence at 4.5 years to the QBO is discussed.