On the understanding of very severe cyclone storm Ockhi with the WRF-ARW model

Abstract

Understanding the dynamics of tropical cyclones (TCs) in terms of intensity, and their trajectory is essential for an adequate early warning and mitigation. The present study attempts to understand the synoptic features of the recent TC Ockhi through a simulation-based approach with the Weather Research and Forecasting (WRF, version 3.8.1) model. Ockhi is considered as a unique TC that originated from depression in the Bay of Bengal on 29 November 2017, recurved towards the Arabian Sea, where it intensified into a very severe cyclone storm and weakened on 5 December 2017. WRF model forced with initial condition from (global forecasting system) GFS data and sea surface temperature (SST) from Group for High-Resolution SST (GHRSST) product for different lead times to test the potential sensitivity of the model. One with an extended period from 20 November to 20 December 2017 (WRF1) and another initiated from 27 November to 6 December 2017 (WRF2). Comparison of the simulated track with the best track estimates from the Indian Meteorological Department indicated an overall track deviation greater than 100 km for both the simulations. The analysis with the extended lead time simulation indicates that the WRF simulated sea level pressure and wind intensity are close to that observed by Arabian sea buoys; CB02, AD08, AD10, and AD07. Daily averaged wind estimate comparison of WRF1 with Scatsat-1 and ERA-5 indicates that the model is slightly overestimating, whereas comparison of peak wind intensity with the time instantaneous swath product of Scatsat-1 leads to underestimation. Analysis of various simulated synoptic features of the cyclone, as discussed in this paper, indicates that the model is skillful in capturing the various stages of cyclone Ockhi.