Tropical Cyclones of the Eastern North Pacific and Their Effects on the Climate of the Western United States: A Study of Circulation Features That May Be Recorded by Tree Rings, Final Report

Abstract

Introduction: In an earlier paper by Douglas (1972) the summer climatology of tropical storm development is reviewed with reference to Sea Surface Temperature (SST) distribution and upper- and lower -level winds. An apparent increase in yearly storm totals recorded since 1965 is believed to be the direct result of satellite detection of small, well off -shore storms. However, monthly variations in storm totals appear to be caused by anomalous SST either off Baja California or along the equator west of South America. During the tropical storm season the region of greatest storm formation is found to shift towards the northwest and then southeast. This regional variation in storm development may be caused by changes in SST and upper troposphere shearing off Baja California and in the movement of the Inter- Tropical Convergence Zone (ITCZ) off mainland Mexico. Data presented by Douglas (1972) indicate that tropical storm formation is most common during the months of July, August and September. During the latter part of August through the first part of October, tropical storms can enter the southwestern United States from either a track up the Gulf of California or up the Pacific Coast of Baja California. This report will review some additional circulation features associated with tropical storm activity in the eastern North Pacific. The major emphasis will be directed towards the effects of these storms upon the climatological conditions of the southwestern United States.