We investigated the variability of one-day precipitation extremes (top 10%) in Tijuana, Mexico during 1950-2000. Interannual rainfall variability is associated with El Niņo/Southern Oscillation (ENSO), which explains 28% of rainfall and 36% of one-day extreme precipitation variance. Interannual precipitation shows a decadal change with a relatively dry period and less variability in 1950-1976 followed by a relatively wet period and more variability in 1976-2000, which appears linked to climatic changes in the Pacific basin. All extreme wet years and the largest frequency of one-day extremes (almost double) occurred after 1976-1977, with 6 out of 8 extreme years characterized by El Niņo episodes and two by neutral conditions. However, almost half of the total frequency of one-day extremes in 1950-2000 occurred during non-ENSO years, evidencing that neutral conditions have an important contribution to extreme climatic variability in the region.

We diagnosed the climate anomalies associated with one-day extreme events for the 1976-2000 period. We found that extremes that occur in neutral (strong El Niņo) conditions are associated with the reverse Pacific/North American (negative Tropical Northern Hemisphere) teleconnection pattern that links an anomalous tropical convective forcing west (east) of the date line with a southward displaced Pacific jet over the study area. We believe that the trough in the jet, typical of these two types of extreme events, is possibly further intensified by thermal interaction with regional anomalies of a warm California Current off Baja California, low-level moisture advection from the subtropical warm sea surface region, and intense convective activity over the study area.