Role of Ocean Heat Content in Rapid Intensification of Tropical Cyclones in the Bay of Bengal

1. IntroductionTropical cyclones (TCs) over the Bay of Bengal (BoB) pose a recurrent and severe threat to densely populated coastal regions of India, Bangladesh, and Myanmar. In recent decades, the phenomenon of rapid intensification (RI)—defined as an increase in maximum sustained winds of at least 30 kt within 24 hours—has become more frequent in the basin. Such events, exemplified by Cyclones Fani (2019), Amphan (2020), and Mocha (2023), have challenged operational forecasting and magnified disaster risk for coastal populations.While sea surface temperature (SST) has long been recognized as a key environmental factor enabling cyclone growth, numerous studies have shown that SST alone is insufficient to explain RI episodes, particularly in regions with strong ocean–atmosphere coupling. The vertical distribution of oceanic heat, expressed as Ocean Heat Content (OHC) and more specifically as Tropical Cyclone Heat Potential (TCHP), provides a better diagnostic of the ocean’s capacity to sustain enthalpy fluxes during strong wind forcing. High OHC prevents cyclone-induced cooling by supporting deeper mixed layers and buffering subsurface entrainment, thereby maintaining favorable thermal conditions during storm passage. Conversely, shallow mixed layers and low OHC promote rapid surface cooling that suppresses intensification.The Bay of Bengal exhibits unique thermodynamic and dynamical features that influence RI. Strong freshwater input from rivers, seasonal monsoon forcing, and shallow shelf regions create variable mixed-layer depths and barrier layers. In addition, mesoscale warm-core eddies and positive sea-level anomalies locally enhance TCHP, often aligning with cyclone tracks. These conditions can modulate whether a developing cyclone undergoes RI or remains at moderate intensity.Although global studies have highlighted the role of subsurface heat in RI, relatively fewer investigations have systematically quantified its impact in the BoB using long-term datasets. Moreover, operational RI prediction by regional meteorological agencies still relies predominantly on atmospheric indicators such as vertical wind shear, mid-tropospheric humidity, and potential intensity. Incorporating oceanic metrics like OHC and TCHP into RI indices may improve predictive skill and provide actionable lead time for warnings.The present study aims to:1. Quantify differences in pre-storm OHC/TCHP between RI and non-RI cases in the BoB during 2000–2024.2. Examine the combined roles of mixed-layer depth, barrier layer thickness, and mesoscale eddies in modulating cyclone–ocean interactions.3. Develop and test a probabilistic RI prediction framework that integrates oceanic and atmospheric parameters.4. Evaluate case studies of recent intense BoB cyclones to illustrate mechanistic pathways.Through this analysis, the paper seeks to improve understanding of the oceanic controls on RI in the Bay of Bengal and assess their potential integration into operational forecasting.