Marine heatwaves (MHWs) and tropical cyclones (TCs) have increasingly impacted the Bay of Bengal (BoB), often compounding spatiotemporally and causing severe damage. This study investigates the mechanisms behind these compound MHW-TC events and their effects on the BoB summer monsoon (BoBSM) onset. Results show that compound events are driven by enhanced net downward shortwave radiation and Ekman downwelling during MHW phase, while abrupt latent heat flux release and Ekman upwelling during TC phase are crucial. The westward shift in TC trajectories in compound events results from cyclonic steering flow and increased maximum potential intensity due to MHWs-related warm sea surface temperature (SST). This shift delays precipitation and latent heat release in the eastern BoB, and the elevated SST, jointly hinder the reversal of the mid-to-upper tropospheric meridional temperature gradient, ultimately delaying the BoBSM onset. These insights into MHW and TC interactions in the BoB offer potential predictability for the BoBSM onset.
 

Marine heatwave,Compound event,Tropical Cyclone；,Monsoon onset,Bay of Bengal