Statistical Forecasting of Tropical Cyclones for Bangladesh

Abstract

Bangladesh being a densely populated country and mostly deltaic region with many people living in thatched cottages along the coast is afflicted severely when lashed by a tropical cyclone (TC). TCs in the region have claimed by far more lives than anywhere else in the world - 49% of the world’s total fatalities by cyclone is in Bangladesh alone and 22% in India (Ali 1996). The tropical cyclones that hit Bangladesh are mostly formed in the Bay of Bengal and their destructive force is primarily due to the accompanying storm surge, whose development is influenced by unique features such as shallow bathymetry and near funnel shape of the Bay (Mandal et al. 2007). As cyclones at different oceans are formed at different times, it is now well established that regional climate and weather patterns play an important role in cyclogenesis (JTWC Annual tropical cyclone reports 2007; Vecchi and Soden 2007). The climate of the region around Bangladesh besides its latitudinal and longitudinal location is influenced by the presence of the highest mountains to its north and northeast. In summer (May-October), a low-pressure system is created in northwest India by heating of landmass that marks the position of the monsoon trough, which causes wind to blow northeast from the Bay of Bengal over the shallow ocean waters to Bangladesh and then get deflected by the mountains to northwest. In winter (November-March), the monsoon trough is over the Bay of Bengal and cold airmass over land in north India moves outward through Bangladesh into the Bay of Bengal in southwest direction. The transition period (May or November) is when the wind is slowest offering ideal conditions for tropical cyclones to form over warm waters.