Recent Trends in Tropical Cyclone Activity in the North Indian Ocean

Abstract

The North Indian Ocean (NIO) which accounts for about 5% of total global tropical cyclones produces about four TCs per year out of which three form in the Bay of Bengal (BOB) and one forms in the Arabian Sea (AS). Because of various socioeconomic factors, these cyclones inflict heavy loss of life and property in the NIO rim countries. Utilizing reliable dataset of satellite era, it has been shown that the stronger TCs with maximum sustained winds (MSW) exceeding 95 nautical miles per hour (knots) and above have become more frequent in the NIO during the past 3 decades. When the frequency of all TCs with MSW exceeding 63 knots is considered, the uptrend reduces. Thus, an increase in the frequency of stronger TCs in NIO during the past few decades is a reality. Extensive work has been done on the changes in the frequency and intensity of TCs of North Indian Ocean (Bay of Bengal and Arabian Sea) by Indian meteorologists (Mooley 1980, 1981; Singh et al. 2000, 2001; Singh 2007; Srivastav et al. 2000). There has been certain amount of ambiguity about the reliability of TC data before the satellite detection of TCs which commenced in the 1970s. For the NIO, the satellite detection of TCs started in 1972 by the Joint Typhoon Warning Centre (JTWC), Guam (now shifted to Pearl Harbor, Hawaii), USA. The India Meteorological Department (IMD) started the satellite detection of TCs from the early 1980s onward when the Indian geostationary satellite, INSAT was launched. The JTWC data on TCs of NIO for 1972-2006 have been used in the present work. Utilizing IMDs existing dataset, a few earlier works (Singh et al. 2001; Singh 2007; Srivastav et al. 2000) have shown that there is an uptrend in the frequency of intense TCs in NIO during the months of high TC activity, i.e., November and May. In the present study, an attempt has been made to derive firm conclusions on recent trends in the annual number of stronger TCs in NIO removing the ambiguity of data of presatellite era.