CR 76:225-240 (2018)  -  DOI: https://doi.org/10.3354/cr01538

ABSTRACT: Summer rainfall along the coast Nayarit, Mexico, behaves in a contrasting way to rainfall observed on the Mexican Altiplano. The mechanism for this behavior originates in the wind flow and moisture content of the atmospheric column. By using field observations from 2015, this study analyzed wind and rainfall characteristics in the interior of the San Pedro-Mezquital river basin, which connects the Pacific coast and the Mexican Altiplano. At the surface, the characteristics of humidity transport that explain rainfall in one region hinder its transport to the other. This has not been previously documented. We further analyzed different scenarios with sets of daily data, using composite maps of average wind and specific humidity at 500, 700, and 1000 hPa to explain these anomalies. In 2015, a pattern resembling the midsummer drought occurred at a weather station located on the coast. The corresponding time series of precipitation, which was derived from an analysis of orthogonal empirical functions with varimax axis rotation, showed that from 1970-2012, there were 3 years (1978, 2000, and 2002) with analysis. The mechanism that caused this behavior originates in the gap in the occurrence of mesoscale convective systems (MCSs), with environmental conditions that provide more convection and enhanced rainfall in September over coastal areas. The September rainfall in these 3 years contrasts that over the Mexican Altiplano, giving more evidence of a seesaw rainfall pattern between these 2 regions.

KEY WORDS: Rainfall · Pacific coast · Mexican Altiplano · Mesoscale convective systems