Modelled impact of ocean warming on tropical cyclone size and destructiveness over the Bay of Bengal: A case study on FANI cyclone

Abstract

Ocean warming influences tropical cyclone (TC) destructive parameters and hence their guidance certainly helps the disaster management agencies to reduce the damage. The present study modelled the sensitivity of TC size, intensity, rainfall, and destructive potential parameters under various ocean warming conditions. A recent extremely severe cyclonic storm FANI (2019) over the Bay of Bengal is chosen for this purpose. The 9-km grid-spacing Weather Research and Forecasting (WRF) model simulations are performed by altering the default sea surface temperature (SST) by −1 °C, +1 °C, +2 °C and, +3 °C respectively along with the control run. The model simulations revealed that ocean warming causes the FANI cyclone to turn northeastward direction. The observed changes of tangential wind speed due to large sea surface enthalpy fluxes associated with ocean warming result in TC size changes and then guide the cyclone to northeastward movement. The radius of 34-knot wind (R34) is more sensitive to the SST warming compared to the radius of maximum winds. The modelled R34 values ranged between ~180–600 km against observations (~100–400 km) during the TC life period. The increased tangential wind speeds (~50–60 m s−1) and convective updrafts (~1.3–1.5 m s−1) in the TC area are responsible for TC intensity and size changes. A linear and exponential growth is seen for the TC destructive potential indicators those estimated using TC intensity and R34 values. The SST increase could result in peak heavy rainfall (>65 mm day−1) in the TC inner-core region, especially the rear sector. The categorical rainfall distribution analysis also proved that heavy rainfall areas extend to greater distances (>300 km) around the TC center with SST warming. The study helps in assessing the hydro-meteorological destruction associated with the TCs in the future warming climate.