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

Abstract

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 ∼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 ∼150°. In addition to the primary steering mechanism, TC vortex propagation can be explained by the strong vertical shear (>30 m·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.

Storm surge hazard over Bengal delta: a probabilistic–deterministic modelling approach

“…A large number of storms is also observed along the eastern coast of Bangladesh. This landfall pattern corresponds to previous observations that the cyclones making landfall on the Bangladesh coastline tend to move north-eastward (Ali, 1996;Akter and Tsuboki, 2021;Mondal et al, 2021).…”

Interdecadal variability of the pre-monsoon cyclone characteristics over the Bay of Bengal

“…This is so that the storm's track and intensity are affected by how the storm is being pushed by the mid-level winds. Because of the influence of 500-300 hPa steering flows, more than half of the TCs over BoB that occurred from 1990 to 2019 recurved from their original path (Akter and Tsuboki 2021). It is found that interaction between westerlies and easterlies at east Indian coastal belts (5-6 m s −1 ) at mid-level during the pre-monsoon season over the BoB basin in the recent decade (figure 5(a)) created a barrier for storms headed towards BGD and MMR while allowing them to take a diversion towards the eastern Indian coastal landmass.…”

Change in cyclone disaster vulnerability and response in coastal Bangladesh

“…Between 2013 and 2017, excluding 2014, four Category 1 cyclones affected the coastal region of Bangladesh: Mahasen in 2013, Komen in 2015, Roanu in 2016, and Mora in 2017; the number of deaths associated with each was less than 50. Studies were undertaken to understand the physical characteristics of these cyclones, their impacts, and the evacuation behaviour of coastal residents (Saha and James, 2017; Akter and Tsuboki, 2021; Rafa, Jubayer, and Uddin, 2021). From a social vulnerability and people‐response perspective, the reasons for not moving to the cyclone shelters and non‐compliance with warning signals during these tropical cyclones were similarly noted as before (Ibrahim, Rahman, and Rezwana, 2019; Chakma and Hokugo, 2020).…”