A Preliminary Analysis of Factors Affecting the Frequency of August Southeastern worth Pacific Tropical Storms and Hurricanes Since the Advent of Satellite Observations

Abstract

Satellite-augmented observations of tropical storm and hurricane frequencies in the southeastern North Pacific during recent Augusts (1966–1974) were compared to various environmental factors. On a regional scale, a relatively strong mean 700 mb ridge from the Gulf of Mexico to Baja California was found to accompany high storm frequency. The linear correlation coefficient between storm frequency and a measure of the strength of this ridge amounted to 0.77. On a larger scale, the 700 mb Subtropical Westerlies Index (20°N to 35°N) for west longitudes from 0° to 180° had a somewhat stronger relation to storm frequency (r=0.86). Average August sea surface temperature in the vicinity of storm formation was poorly correlated with storm frequency. This suggests that the unfailingly warm August water temperatures in this area— always exceeding 27°F—were not a limiting factor in storm development.