The Mexican Monsoon

TLDR

The warm‑season rainfall maximum over southwestern North America, most pronounced in New Mexico and southern Arizona, has been noted by investigators and is an extension of a larger‑scale phenomenon centered over northwestern Mexico. The study aims to explain the observed precipitation distribution and timing of the Mexican monsoon, which cannot be accounted for by monthly mean upper‑air wind and moisture patterns. The authors analyze monthly mean rainfall, geostationary satellite imagery, and rawinsonde data to describe the Mexican monsoon. The study finds that the Mexican monsoon has a defined geographical extent and magnitude, a rapid onset, and peaks in a specific month during summer.

Abstract

The pronounced maximum in rainfall during the warm season over southwestern North America has been noted by various investigators. In the United States this is most pronounced over New Mexico and southern Arizona; however, it is but an extension of a much larger-scale phenomenon that appears to be centered over northwestern Mexico. This phenomenon, herein termed the “Mexican monsoon,” is described from analyses of monthly mean rainfall, geostationary satellite imagery, and rawinsonde data. In particular, the authors note the geographical extent and magnitude of the summer rains, the rapidity of their onset, and the timing of the month of maximum rainfall. Finally, the difficulty in explaining the observed precipitation distribution and its timing from monthly mean upper-air wind and moisture patterns is discussed.