Stable isotope tempestology of tropical cyclones across the North Atlantic and Eastern Pacific Ocean basins.

Tropical cyclones (TCs) are one of the major natural hazards to island and coastal communities and ecosystems. However, isotopic compositions of TC-derived precipitation (P) in surface water (SW) and groundwater (GW) reservoirs are still lacking. We tested the three main assumptions of the isotope storm "spike" hypothesis (sudden spikes in isotopic ratios). Our database covers 40 TCs and is divided into recent (N = 778; 2012-2023) and archived (N = 236; 1984-1995) rainfall isotope observations and SW/GW isotope monitoring (N = 6013; 2014-2023). Seasonal rainfall contribution from TCs ranged from less than 1% to over 54% (4% on average) between 1984 and 2023. Mean δ18O compositions across TCs domains were significantly lower than the regional (noncyclonic) δ18O mean (-5.24 ± 4.27‰): maritime (-6.29 ± 3.28‰), coastal (-7.78 ± 4.28‰), and inland (-9.80 ± 5.18‰) values. Coastal and maritime TC convection resulted in large rainfall amounts with high isotope compositions. This could bias past climate reconstructions toward unrealistic drier conditions. Significant δ18O and d-excess differences were found between storm intensities. P/SW and P/GW isotope ratios revealed the rapid propagation of TC excursions in freshwater systems. Our findings highlight the potential of TC isotope observations for diagnosing intensity and frequency in paleoproxies beyond idealized TC models.