Upper-Ocean Control on Cyclone Thane Evolution Near Landfall: Insights from Genesis Potential Indices and In-Situ Observations

: Tropical cyclone evolution near landfall is strongly influenced by coupled ocean–atmosphere interactions, particularly upper-ocean thermal structure and coastal ocean processes. While atmospheric Genesis Potential Indices (GPIs) are widely used to identify cyclone-favorable environments, their capability to represent oceanic influences during the pre-landfall and landfall stages remains limited. This study investigates the Extremely Severe Cyclonic Storm Thane (December 2011) over the Bay of Bengal (BOB) using three Genesis Potential Indices: the atmospheric-based index (GPIK), an ocean-modified index incorporating Upper Ocean Heat Content (GPIS), and an enhanced ocean-modified index that additionally includes Sea Surface Height Anomaly (GPIS1). Rather than developing new indices, this study evaluates the performance of these atmospheric- and ocean-modified GPIs during a well-observed cyclone event by integrating atmospheric reanalysis with high-resolution in-situ observations from tide gauges, wave rider buoys, and moored buoys. The results show that cyclone-favorable conditions intensified as Thane approached landfall. Compared with the atmospheric-only index, GPIS and GPIS1 exhibited stronger and more persistent signals, increasing the index magnitude by approximately 40–60% and 70–100%, respectively. GPIS1 showed the closest agreement with the observed cyclone evolution, highlighting the importance of incorporating upper-ocean thermal and dynamic conditions into GPI formulations. Independent observations confirmed storm-surge development, enhanced significant wave heights, and upper-ocean cooling associated with intense vertical mixing, consistent with the environmental conditions represented by the ocean-modified indices. This case study demonstrates that integrating ocean-modified GPIs with independent coastal observations provides improved physical insight into the role of upper-ocean conditions in cyclone intensification, translation speed, and coastal impacts during Cyclone Thane. The findings support further evaluation and refinement of ocean-integrated cyclone prediction frameworks for improved tropical cyclone monitoring and forecasting over the BoB.