El Niño–Southern Oscillation and Interannual Variability of Thunderstorm-Day Frequency in Mexico (1991–2020)

Thunderstorms in Mexico have recently attracted increased study. However, researchers have not systematically evaluated the relationship between thunderstorm activity and the El Niño–Southern Oscillation (ENSO) at the national scale. This study examines the association between ENSO and thunderstorm-day frequency across Mexico from 1991 to 2020, utilizing data from the Global Surface Summary of the Day and the Oceanic Niño Index (ONI). Standardized monthly thunderstorm-day anomalies were correlated with ONI at lags of 0 to 3 months and across four climatological seasons. Thunderstorm activity increases beginning in May, peaks during boreal summer, and declines in autumn, with considerable spatial variation among stations. At the national scale, thunderstorm-day anomalies show a weak but statistically significant positive correlation with ONI (r = 0.24, p < 0.001), i.e., higher ONI values were generally associated with positive standardized anomalies in thunderstorm-day frequency. Significant station-level relationships are limited and predominantly positive, with 18 of 48 stations exhibiting significant correlations, 17 of which are positive. No systematic strengthening of the relationship is observed when ONI leads thunderstorm activity by 1 to 3 months. Seasonal analyses suggest pronounced geographic variability and sign changes in correlations. Overall, ENSO imparts a detectable but limited statistical signal in Mexican thunderstorm variability, with the magnitude and direction of this relationship strongly dependent on location and season.