Role of Anomalous Ocean Warming on the Intensification of Pre‐Monsoon Tropical Cyclones Over the Northern Bay of Bengal

Abstract

AbstractThe northern Indian Ocean, typically the Bay of Bengal (BoB), has experienced several stronger tropical cyclones during the pre‐monsoon season in the last few years. Similarly, in 2021, cyclone Yaas reached the Very Severe Cyclonic Storm (VSCS) stage despite forming above 14°N. In comparison to the other three cyclones that formed in 2007 (Akash), 2009 (Aila), and 2017 (Mora) with a similar cyclogenesis location and track, the pre‐cyclonic condition in 2021 is more favorable. It was found that from 2007 to 2021, the area associated with Sea Surface Temperature greater than 31°C increased from 0.1 percent to 29 percent. The Research Moored Array for African‐Asian‐Australian Monsoon Analysis and Prediction buoy at 15°N also recorded an increasing trend of 0.1°C per year in both average and maximum temperatures during May. The warming in 2021 is primarily linked with Marine Heat Wave events, which extensively cover the north BoB for a longer duration starting from the first week of May. Such warming extends even to the subsurface, providing the heat required to convert the depression into VSCS within 2 days. The weaker western boundary current during 2021 made the northern BoB fresher and favorable for cyclone, intensification. The associated anticyclonic eddy along the track extended the abnormal distribution of low saline water even up to the subsurface (∼100m), which is vital in increasing the ocean heat content. These simultaneous pre‐cyclonic oceanic conditions can be incorporated into the weather model to understand and predict the rapid intensification within a shorter duration.