Withdrawal of Southwest monsoon will lead to the onset of Northeast monsoon in the Indian sub-continent. Indian seas become the hot activity centers for cyclones during this period. Bay of Bengal and Arabian Sea , both, have historically been the deadliest basin with several cyclones responsible for catastrophic damage. Cyclonic disturbances may originate over the Indian seas or occasionally, the remnant of Pacific Ocean systems could enter Bay of Bengal to become tropical storm later. Though, frequency of storms is more in Bay of Bengal, in comparison to Arabian Sea but severity takes almost equal toll.
High level of heat potential is the basic requirement for development of storms. Few other conditions favourable for formation of cyclonic storm are as given below:
- Tropical cyclones develop in the vicinity of Inter Tropical Convergence Zone (ITCZ) or near equatorial trough
- Tropical cyclones develop in maritime airmass over sea areas where Sea Surface Temperature (SST) is more than 26 deg centigrade and overlying tropical atmosphere is convectively unstable
Apart from the strong spiralling winds, torrential rains and high seas, the storm piles up in its forward sector, a huge sheet of sea water, a few meters high which can inundate low lying coastal areas causing large scale death and devastation. This is called the storm surge, which, coupled with strong winds become the most destructive feature associated with the storm. A fully matured cyclone develops a calm center or EYE with a ring of hurricane winds around it. But many cyclones may not develop to this stage.
Tropical cyclones are more complex and difficult to predict. They are notorious for rapid changes in their intensity and track, as well, defying the timelines many a times. Fifteen of the deadliest tropical storms in the world history have been Bay of Bengal storms that have hit Bangladesh, India and Myanmar. They strike the coast and weaken as they move inland because of the cut off of the moisture which is their main source of energy. While the stage is set for the onset of Northeast monsoon over the southern peninsula, disaster mitigation and management agencies need to gear up for any such eventuality.
