Understanding the role of ocean and atmosphere during the genesis and intensification of post-monsoon cyclones in the Bay of Bengal

This study investigates the role of the ocean–atmosphere interaction of three strong cyclones named Phailin, Hudhud, and Bulbul during the post-monsoon in the Bay of Bengal. Phailin and Hudhud were extremely severe cyclonic storms, whereas Bulbul reached the very severe cyclonic storm category. This work shows the atmospheric and ocean surface conditions during their cyclogenesis and intensification. Sea surface temperature, horizontal wind, absolute vorticity, latent heat flux, vertical wind shear, and relative humidity are analyzed to elucidate the causes of the contrasting characteristics of these cyclones. We found that very high sea surface temperatures (30–31.5 °C) and their anomalies (0.8–1.6 °C) and high tropical cyclone heat potential (120–140 kJ cm–2) were present over the tropical cyclone genesis and intensification points for the Bulbul cyclone. The high relative humidity (> 90%) over the genesis location, combined with low wind shear (< 5 ms−1 for the Phailin and Hudhud cyclones, creates favourable conditions for cyclogenesis. The lower-level wind was much stronger (> 14 ms−1) for the Phailin and Hudhud cyclones which enhanced convergence and vorticity. During the cyclonic period, these cyclones exhibit a distinctively increased distribution of net heat flux with high values (220–280 Wm−2) concentrated over the central, northern regions of BOB and in the vicinity of cyclone tracks.