Extreme Rainfall Contribution and Isotopic Excursion of Tropical Storm Alberto in Northeastern Mexico

ABSTRACT Rationale Tropical cyclones are critical extreme rainfall events that can temporarily mitigate drought impacts in semiarid regions. Despite the well‐known North Atlantic hurricane season, the propagation of isotopically distinct rainfall pulses across semiarid landscapes of Mesoamerica is largely unknown. Methods In June 2024, tropical storm (TS) Alberto made landfall in northeastern Mexico. This study evaluates TS Alberto's monthly and annual rainfall contribution across Tamaulipas and Nuevo León and the isotopic excursions (δ 18 O and d ‐excess) in precipitation and surface water. Rainfall data from 86 stations and high‐frequency isotope samples from Ciudad Victoria, Tampico, Chetumal, and the San Marcos River were analyzed. Results Results show that TS Alberto produced unprecedented rainfall, ranging from 0.22 to 11.41 times the 10‐year June average, and up to 123% of the annual average in orographically influenced regions (i.e., variation is based on 86 locations across the region). Reservoir data highlight a rapid hydrological recovery, with dam levels in Tamaulipas and Nuevo León increasing significantly within weeks. Rainfall isotopic composition exhibited a broad spectrum (δ 18 O: −15.82‰ to −2.80‰), reflecting varying moisture sources, convective activity, and orographic effects. TS Alberto reproduced nearly the entire annual δ 18 O variability within a few hours, underscoring the strong isotopic imprint of extreme events. During TS Alberto's landfall and passage, an inverse trend between δ 18 O and precipitation amount was observed. Conclusions The storm's isotopic signature was traced into surface waters, providing evidence of rapid river response and potentially for aquifer recharge. These findings emphasize the dual hydrological and isotopic role of TCs in modulating water scarcity and improving hydroclimate reconstructions in drought‐prone landscapes.