Impact of varying landfall time and cyclone intensity on storm surges in the Bay of Bengal using ADCIRC model

This study focuses on the impact of varying landfall timing in a tidal cycle (i.e., the spring-neap phase) and varying wind speeds (i.e., cyclone intensities) on the surge tides for the tropical cyclone Fani in the Bay of Bengal using a hydrodynamic finite element-based 2D (ADvanced CIRCulation) ADCIRC model setup. For atmospheric forcing, the Cyclostrophic Symmetric Holland wind Model (H80) and Generalized Asymmetric Holland Model (GAHM) model are used to estimate the wind fields from the IMD best track data. Comparisons with in-situ winds from moored buoys within the proximity of cyclone track showed that H80 simulated winds underestimate the observed winds in terms of magnitude followed by a mismatch in the wind directions as well. In contrast, the GAHM simulated wind fields, which are statistically better in terms of both magnitude and direction are used for different wind experiments. To understand the impact of the varying landfall timing and varying wind speeds on storm surges, a series of sensitivity experiments have been performed during a tidal cycle with modulated high and low winds along the cyclone track. The experiments considering varying landfall timing during a tidal cycle indicate the strongest surge tides (1.99 m) during the spring high tide phase, whereas the lowest surge tide of 0.94 m is observed during spring low tide. However, the surge tide at the actual time of landfall is 1.20 m which is during the transition from low tide to high tide. On the other hand, the combined impact of wind speeds and varying landfall timing indicated the strongest surge tides of 2.25 m during high wind conditions associated with spring high tides. In contrast, the surge tides decrease significantly during low tide and low wind conditions. This study confirms the importance of both winds and landfall timing on the storm surges, which will be crucial to forecast the storm surges associated with the tropical cyclones.