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With limited groundwater reserves and few reservoirs, Caribbean islands such as Puerto Rico are largely dependent on regular rainfall to meet societal and ecological water needs. Thus, the ability to anticipate seasonal rainfall shortages, such as the 2015 drought, is particularly important, yet few reliable tools exist for this purpose. Consequently, interpolated surface precipitation observations from the Daymet archive are summarized on daily, annual, and seasonal time scales and compared to the host thermodynamic environment as characterized by the Galvez-Davison index (GDI), a convective potential parameter designed specifically for the tropics. Complementing the Daymet precipitation totals, >= 1.1 million WSR-88D volume scans between 2002 and 2016 were analyzed for echo tops >= 10 000 ft (similar to 3 km) to establish a radar-inferred precipitation activity database for Puerto Rico. The 15-yr record reveals that the GDI outperforms several midlatitude-centric thermodynamic indices, explaining roughly 25% of daily 3-km echo top (ET) activity during each of Puerto Rico's primary seasons. In contrast, neither mean-layer CAPE, the K index, nor total totals explain more than 11% during any season. When aggregated to the seasonal level, the GDI strongly relates to 3-km ET (R-2 = 0.65) and Daymet precipitation totals (R-2 = 0.82) during the early rainfall season (ERS; April-July), with correlations weaker outside of this period. The 4-month ERS explains 51% (41%) of the variability to Puerto Rico's annual rainfall during exceptionally wet (dry) years. These findings are valuable for climate downscaling studies predicting Puerto Rico's hydroclimate in future atmospheric states, and they could potentially be adapted for operational seasonal precipitation forecasting.