Intense humid heat ─ tropical cyclone compound hazards in eastern coastal India

Abstract The eastern coast of India is a hotspot of both heatwaves and tropical cyclones (TCs). However, the potential for TCs to trigger or contribute to subsequent humid heatwaves over land (HHLs) remains unexplored. We assess compound interactions between marine heatwaves (MHWs), landfalling TCs, and HHLs during 1982–2023 at the Bay of Bengal (BoB), considering 33 urban and peri-urban sites within 200 km of coastline. HHLs at these sites demonstrate a significant upward trend, increasing from ~2 events/year in 1982−1991 to 6 events/year in 2014−2023. In contrast, TC-compounded HHLs—comprising 17% HHLs—maintain a stable frequency of ~1.4 events/year. In half of these compound extremes, HHLs follow TCs, often with ~8% higher HHL magnitudes within 5 days of landfall compared to uncompounded HHLs, especially for coastal sites. During the post-monsoon season, 33% of at-site record HHLs follow TCs, with record compounded HHL magnitudes exceeding up to 14% of record uncompounded HHL magnitudes. Meanwhile, over broad ocean areas, MHWs precondition up to 50% of TCs, and strong MHWs precondition up to 33% of rapidly intensified (RI) TCs; for the study sites, up to 50% of RI TCs are followed by HHLs. TC-heat compounding in the BoB—largely affected by MHW−TC−HHL event chains—occurs at rates (identified using seasonally varying thresholds) that notably exceed the previously reported global averages based on fixed thresholds.