Sub-seasonal variability of tropical cyclone landfall characteristics on the west coast of the Bay of Bengal during October–December: The role of La Niña and El Niño

Abstract

Tropical cyclones (TCs) create more disasters when they make landfall. Climatologically, the west coast of the Bay of Bengal (BoB), one of the most densely populated geographical regions over the globe, is more vulnerable to TC landfall during the primary TC season (October–December), with around 72% of TCs originating in the BoB making landfall on the west coast of BoB (WCBoB). However, the evidence for reliable interannual modulation of sub-seasonal variability on landfalling TCs during the primary TC season in the BoB has been explored less. Here, we used the 35 years (1988–2022) of best TC track data from the BoB to investigate this aspect. Those TCs that made landfall on the WCBoB indicate a significant meridional shift between the first and second half of the primary TC season in the La Niña regime, with 93% (83%) of TC formed in the first (second) half of the season making landfall in the north WCBoB (south WCBoB). Our study reveals that the meridional shift in genesis location and difference in steering flow between the first and second halves of the season is principally responsible for the sub-seasonal variability of landfall location in the La Niña regime, in which former characteristics seem to be determined by southward propagation of Genesis Potential Index (GPI). GPI magnitude is lower in the El Niño regime than in the La Niña regime during the primary TC season, resulting in lower TC activity without sub-seasonal variability in the landfall characteristics in the BoB.