Understanding the dynamics of tropical cyclones (TC) in terms of intensity, and their trajectory is essential for 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 Nov 2017, recurved towards the Arabian Sea, where it intensified into a very severe cyclone storm and weakened on 5 Dec 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 Nov to 20 Dec. 2017 and another initiated from 27 Nov to 6 Dec 2017. Comparison of the simulated track with the best track estimates from the Indian Meteorological Department (IMD) indicated an overall track deviation greater than 100Km for both the simulations. The analysis with the extended lead time simulation indicates that the WRF simulated sea level pressure (SLP) 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.
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<p>The Northern Indian Ocean has witnessed the genesis of several devastating cyclones over the years due to the typical warm climate. The effect of climate change on these cyclones is an essential topic of research owing to the socio-economic impacts of these cyclones on the coastlines. Climate change is expected to influence the various synoptic parameters of these storms, like translational speed, intensification, frequency, etc. Most of the studies about the impact of climate change on cyclones have been done related to the Atlantic and Pacific Oceans; very few have explored the storms of the Indian Ocean in this context. Considering this context, the present study attempts to understand the track, intensity, and synoptic parameters of Tropical cyclone Vayu-June 2019 under the climate change scenario of RCP 8.5 with the Community Earth Systems Model, CESM data simulated with GPU-based WRF-ARW model. The model is simulated at a 9km single domain with a selected set of physical settings based on the previous studies on the cyclones of the Northern Indian Ocean. The track and intensity of the simulated storm are compared with the present-day hurricane Vayu from the IMD best track estimates.</p>
<p>Interestingly under RCP 8.5, unlike the present-day cyclone Vayu, under RCP 8.5, Vayu would have made landfall along the west coast of India with a sustained wind speed of ~ 15 m/s w. At the same time, he presents a scenario in Vayu weakened over the ocean due to several interactions with the mid-latitude westerlies. The results indicate a considerable change in the future thermodynamics under which Vayu sustained the intensity till landfall. Under RCP 8.5 simulations, the initial posting error is high; other than that, the coming cyclone Vayu seemed to follow a similar track as the present-day storm except for the landfall.</p>
<p>Regarding wind speed intensity, Vayu under RCP 8.5 shows equal wind intensity as that of the present day, with similar underestimation at the mature stage of the storm. The initial results of this study indicate that changes in large-scale thermodynamics in future warming scenarios can influence the modulations in track and intensity of a very severe cyclonic storm like Vayu. Such results highlight the importance of closely monitoring Arabian Sea cyclones to understand the impending disaster mitigations under probable warming scenarios.</p>
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