Mean rainfall characteristics of tropical cyclones over the North Indian Ocean using a merged satellite-gauge daily rainfall dataset

The tropical cyclones (TCs) formed over the North Indian Ocean (NIO) have paramount socio-economic impacts over India and neighbouring countries due to heavy rainfall, strong wind and high storm surge. In this study, mean rainfall characteristics of three different intensity stages of TCs over the NIO have been examined using a merged satellite-gauge daily rainfall product to better TC rainfall prediction over the region. A total of 32 TCs with 160 days of rainfall over the NIO between October 2015 and December 2021 have been considered. The mean positions of TCs formed over the AS are more than 450 km west during the post-monsoon season than the pre-monsoon season. During the post-monsoon TCs, mean translational speed increases with increase in TC intensity over the Bay of Bengal (BoB), while TCs in the Arabian Sea (AS) move rather slower with increase in intensity. Heavy TC rainfall areas have seen to be larger during the pre-monsoon season than the post-monsoon season over both BoB and AS basins. It is due to smaller mean sea level pressure, and stronger lower and middle level winds over both basins of the NIO during the pre-monsoon season as compared to the post-monsoon season. However, intensity of mean rainfall is higher for the TCs over the AS than the BoB during the pre-monsoon season. Heavy rainfall radius is maximum for depression and deep depression stages of TCs during the pre-monsoon season, while it is maximum for cyclonic storm and severe cyclonic storm stages of TCs during the post-monsoon season over both basins of the NIO. The largest heavy rainfall radius of about 650 km in the northeast geographical quadrant is observed for the pre-monsoon depression and deep depression stages of TCs over the BoB basin. The most intense daily rainfall occurs during the pre-monsoon TCs and the least intense daily rainfall occurs during the post-monsoon TCs over the AS basin. A consistent increase in daily maximum rainfall and decrease in its distance from the TC centre with the increase in TC intensity are observed over the AS for both seasons. The distance of maximum daily rainfall grid from the TC centre is the largest of about 355 km for depression and deep depression stages of TCs formed over the AS during both pre-monsoon and post-monsoon seasons. Furthermore, results indicate that translational speed of TCs has no impact on daily maximum rainfall over the BoB, whereas daily maximum rainfall shows statistically significant negative correlation with the TC translational speed over the AS. This study will be very useful for better TC rainfall forecasting over the NIO region.