The largest number of tropical cyclones (TCs) is generated in the northeastern Pacific Basin. These storms can produce extreme precipitation (EP) in northwestern Mexico, causing loss of life and environmental damage. It is important to understand the dynamics that cause the EP associated with TCs, since most human activity requires planning to adjust to the dynamics of local climate changes. Therefore, in this work the goal was to estimate the trends and return periods of the average annual daily extreme precipitation (AADEP; 95th percentile, P95) in the June-September season in the core North American monsoon. To do this, daily precipitation data from 1961 to 2000 from 48 climate computing (CLICOM) weather stations located in the core of the North American monsoon were used to determine AADEP:
1. Non-parametric trends with Mann-Kendall tests and Sen’s slope estimator.
2. Linear trends of annual averages of 95 (P95) and 99 (P99) percentiles with the least squares method.
3. Return periods with the Gumbel frequency distribution function. The results disclose a significant upward trend in the intensity of P95 increases in mountain stations, which may be related to a greater contribution of precipitation associated with TCs.
The seasonal contribution of P95 in coastal stations and the total monsoon precipitation did not show statistical significance at α = 0.05. The return periods of P95 associated and not associated with TC’s from 2005 to 2500 were calculated. Return periods of P99 have been rising since 2010 and will continue to 2500. For P95 events associated with TCs, the anomalies are expressed with synoptic conditions of simultaneous positive anomalies in the Pacific Decadal Oscillation (+PDO), negative anomalies in the Atlantic Multidecadal Oscillation (-AMO), weak La Niña in the eastern equatorial Pacific, positives in Caribbean Sea temperatures (SST>28.5ºC) and a strong land-sea thermal contrast in northwestern Mexico. The synoptic conditions were created two weeks before the start of TCs. This work sheds new light on the dynamics of return periods of EP and P95 trends associated with TCs, and on current and future simultaneity between anomalies of the +PDO and -AMO, which are essential characteristics for knowledge of TC for one of the regions most affected by these phenomena worldwide.