We study the impacts of in utero exposure to Hurricane Catarina of March 2004, the first hurricane to hit Brazil. Catarina was unexpected and is representative of other recent hurricanes in the Americas in terms of wind speed, direct economic costs, and population affected. We use a triple-differences strategy (close vs. far municipality, 2004 vs. 2003, after March vs. before) to highlight the importance of flexibly accounting for season of birth effects. We find that the adverse effects of exposure are concentrated among babies born to mothers 15-24 years old: birth weight decreased by 82 g, the probability of being born low birth weight increased by 3.4 pp, and fetal deaths increased by about 17 per 1,000 live births and fetal deaths. These impacts are not explained by reductions in employment or healthcare use. Maternal stress is a plausible mechanism if younger women are more financially vulnerable to negative shocks, consistent with recent work highlighting the relationship between socioeconomic status, stress, and birth outcomes. Our findings are robust to various checks, including testing for pre-trends in infant health outcomes.