Investigation of unique Arabian Sea tropical cyclone with GPU-based WRF model: A case study of Shaheen

Abstract

The recent severe cyclonic storm (SCS) Shaheen was a rare and unique Tropical Cyclone (TC) formed on September 30, 2021, on the Saurashtra coast off Gujrat, from a depression remnant of another cyclone Gulab off the Bay of Bengal. Under the influence of warm waters, this unique storm travelled westwards, skirting Pakistan's Makran coast before making landfall on northern Oman on October 4, 2021. The present study attempts to understand cyclone Shaheen's track, intensity, and synoptic features with the GPU-based WRF-ARW (v-3.8.1) on the google cloud platform (GCP). A 9 km resolution model domain covering the cyclone's track is initiated with an 18 UTC cycle of the Global Forecasting System (GFS) data. The model skilfully captured Shaheen's track and intensity up to 24 h of lead time which was in close agreement with the India Meteorological Department (IMD) estimates. The simulated track showed an overall track error of approximately 73 km compared to IMD. However, the surface wind stress was in close agreement with IMD. The spatial-temporal analysis of the simulated maximum surface wind speed showed the formation of the distinct eye of the cyclone moving away from the Indian coast towards the Gulf of Oman. Results indicated that Shaheen had a strong low-level (850 hPa) relative vorticity of approximately 193.56 10-5s-1 on 2nd October during the matured severe cyclonic stage, which got reduced to 77.88 × 10-5s-1 on 4th October as the system weakened. Comparison of the simulated synoptic parameters of the storm with reanalysis datasets ERA-5 and NGFS datasets indicated that the model simulated a stronger TC. The cyclone system showed significant relative humidity of about 80–90% with the well-delineated eyewall throughout various stages. The study shows the GPU-based WRF model's reliability with the current set of parameterizations for investigating a unique TC, Shaheen, on a public cloud infrastructure.