Data Assimilation Experiments with ARW–3DVAR for Tropical Cyclone Extreme Weather Predictions Over Bay of Bengal

Tropical cyclones (TCs) are highly disastrous weather phenomena characterised with extreme winds, heavy precipitation and storm surges at landfall along coastal lands. Accurate prediction of the TC formation, movement and intensity is vital for early warning and disaster management. The favourable environmental conditions have been identified as presence of an initial disturbance in the form of incipient lows or tropical easterly waves, high sea surface temperature (SST) (≥26.5 °C) for transport of energy through air–sea fluxes, weak vertical wind shear in the 850–200 hPa layer conducive to large-scale cloud development and divergence in the upper atmosphere to facilitate further surface-level convergence and for overall sustenance of the system (Anthes TCs: their evolution, structure and effects. American Meteorological Society, Science press, Ephrata, p 208, 1982; Gray General characteristics of TCs. In: Roger P,Jr, Roger P, Sr (eds) Storms, vol 1. Routledge, 11 New Fetter Lane, London EC4P4EE. pp 145–163, 2000). The annual average frequency of TCs in the North Indian Ocean (NIO) is about five (Asnani Tropical meteorology, vols. 1 and 2, published by Prof. G.C. Asnani, c/o Indian Institute of Tropical Meteorology, Dr. HomiBhabha Road, Pashan, Pune 411008, India, 1993). Numerical prediction of TCs requires accurate specification of initial conditions that define the characteristics of an incipient storm in terms of its location, radius, central pressure, and tangential and vertical winds.