Role of coastal downwelling on the intensification of post-monsoon tropical cyclones in the Bay of Bengal

The present study investigates the role of coastal downwelling in the intensification of tropical cyclones before landfall near the coastal Bay of Bengal (BoB) during the post monsoon season. Four major cyclones (Phailin, Hudhud, Titli, and Gaja), whose maximum intensity is equivalent to a very severe cyclonic storm or higher, with a wind speed of more than 64 knots, are considered in this study. It was found that higher Sea Surface Temperature (SST) (similar to 30 C-degrees) conditions prevailed near the coastal BoB for all four cyclones a week before landfall. This was primarily attributed to coastal downwelling, which was identified by a positive sea level anomaly along the west coast of the Bay of Bengal during the post-monsoon season. This phenomenon results in the deepening of the isothermal layer, leading to an increase in Ocean Heat Content and ultimately contributing to the sustained higher SST in the nearby region of their landfall. The low-saline freshwater influx advected by the southward coastal current also helps to maintain the warm temperature of the upper layer. Coastal downwelling raises the ocean heat content near the coast, which provides the energy needed to intensify cyclones before landfall. These findings show the importance of coastal downwelling when simulating the short-term evolution of near-shore oceanic conditions, allowing us to improve the prediction of changes in tropical cyclone intensity prior to landfall.