Recurvature and movement processes of tropical cyclones over the Bay of Bengal

Active bimodal tropical cyclones (TCs) are embedded in nonuniform flows over the Bay of Bengal (BoB). More than half of the TCs that occurred from 1990 to 2019 recurved from their original path due to the influence of 500-300 hPa steering flows. Premonsoon TCs have a tendency to turn right and make landfall on the right-side coastal areas of the BoB. On the other hand, most of the TCs that occurred in the postmonsoon season crossed the left coast or east coast of India, despite being left or right from their path. The simulation shows that Cyclone Roanu (2016) was driven by a warm, moist, unstable southwesterly that was blocked and diverted by the hot, dry stable air masses of northerlies and northwesterlies. As a result, the TC moved along the dry-moist boundary, keeping a constant distance of similar to 400 km between the eye and dryline. Conversely, the combined steering of moist southeasterly and southward-moving upper-level westerly jets controlled the track of postmonsoon Cyclone Madi (2013), encompassing a left turn of similar to 150 degrees. In addition to the primary steering mechanism, TC vortex propagation can be explained by the strong vertical shear (>30 m center dot s(-1)) offered by the dryline during the premonsoon period and near the monsoon trough in the postmonsoon period. This vertical shear causes the upper-level anticyclone to tilt downshear, resulting in the forward motion of the TC vortex. The deep convection and associated mesovortices, especially those that are more prominent along the dryline, additionally influence asymmetric diabatic heating, contributing to the advection of TC potential vorticity.