Tropical Cyclone Track, Structure and Intensity Changes at Landfall

Abstract

Cyclone Warning Division of India Meteorological Department (IMD), New Delhi acts as a Regional Specialised Meteorological Centre (RSMC) for north Indian Ocean (NIO) and provides tropical weather outlook and tropical cyclone (TC) advisories to the World Meteorological Organisation (WMO)/Economic and Social Cooperation for Asia and the Pacific (ESCAP) Panel member countries, viz., Bangladesh, Myanmar, Thailand, Srilanka, Maldives, Pakistan and Oman. The low pressure systems over the NIO are classified (Table 1) based on the associated maximum sustained surface wind (MSW) at the surface level (IMD, Cyclone warning services: standard operation procedure. Cyclone warning division, IMD, New Delhi, 2013a). The entire process of TC monitoring and forecasting (Mohapatra et al., Mausam 64:1–12, 2013a) is shown in a schematic diagram (Fig. 1). Like other Ocean basins, the TCs over the NIO also show sometimes significant changes in track, structure and intensity prior to, during and after the landfall. Out of 5–6 TCs developing over the NIO, about 3–4 make landfall (Tyagi et al., Inter-annual variation of frequency of cyclonic disturbances landfalling over WMO/ESCAP Panel Member Countries, WMO/TD-No. 1541 on Ist WMO International conference on Indian Ocean Tropical Cyclones and climate change, Muscat, Sultanate of Oman, 08–11 March 2009, WWRP-2010/2, pp 1–7, 2010; Mohapatra et al., Construction and quality of best tracks parameters for study of climate change impact on Tropical Cyclones over the North Indian Ocean during satellite era. In: Mohanty UC, Mohapatra M, Singh OP, Bandyopadhyay BK, Rathore LS (eds) Monitoring and prediction of Tropical Cyclones over the Indian Ocean and climate change. Springers/Capital publishers, New Delhi, pp 1–17, 2014). The strategies adopted by RSMC, New Delhi to predict the changes in track, structure and intensity of landfalling TCs along with difficult situations and future plans are presented in following sections. Table 1 Classification of cyclonic disturbances over the NIO (since 2015) Low pressure system Maximum sustained surface winds (knots) Number of closed isobars at interval of 2 hPa within 5° latitude/longitude square Low pressure area <17 1 Depression 17–27 2 Deep depression 28–33 3 Cyclonic storm 34–47 4–7 Severe cyclonic storm (SCS) 48–63 8–10 Very severe cyclonic storm (VSCS) 64–89 11–25 Extremely severe cyclonic storm (ESCS) 90–119 26–39 Super cyclonic storm (SuCS) 120 and above 40 or more Open image in new window Fig. 1 Monitoring and forecasting process of tropical cyclone (after Mohapatra et al. 2013a)