Numerical simulations of tropical cyclones Amphan and Nisarga with incorporation of sea surface temperature in the model

The study mainly focuses on the simulation of the tropical cyclone track by incorporating sea surface temperature (SST) in a Numerical Weather Prediction (NWP) Weather Research and Forecasting (WRF) model. In the present work, two tropical cyclones viz, Super Cyclonic Storm (SuCS) Amphan (16th to 21st May 2020) and Severe Cyclonic Storm (SCS) Nisarga (1st to 4th June 2020) are used as case studies, which formed over the Bay of Bengal and Arabian Sea respectively in the year 2020. The simulation was performed up to 72 hours. The 6-hourly National Centers for Environmental Prediction (NCEP) data at 1°×1° spatial resolution is used to define the model initial and boundary condition and daily real time global SST analysis (RTG_SST) data is used to initialize the model. SuCS Amphan is simulated for five different sets of initial conditions (ICs) (IC=00Z of 16 May 2020, 00Z of 17 May 2020, 00Z of 18 May 2020, 00Z of 19 May 2020 and 00Z of 20May 2020) and SCS Nisarga is simulated for three different ICs (IC=00Z of 01June 2020, 00Z of 02June 2020 and 00Z of 03June 2020). The track error and landfall position error are computed using the India Meteorological Department (IMD) best track. The landfall error has also been calculated and compared with IMD landfall observation. Other parameters, such as maximum sustained surface wind, central pressure and rainfall, have also been estimated and compared with the observational data from IMD and satellites. The 12-hourly average track error has been computed and the value varies from 22.5 km to 105.5 km for SuCS Amphan and 36.9 km to 112.8 km for SCS Nisarga for 12 to 72 hour lead time.