• In the last 50 years, the coastal region of Andhra Pradesh — from Srikakulam to Nellore — would have been hit by at least 70 cyclones, a few of them categorised as Category 3 to Category 5 levels of cyclonic storm.
  • India basically has two seasons prone to tropical cyclones — one from April to May, which is just prior to the onset of southwest monsoon, and the other from October to November, a period when the southwest monsoon ends and the northeast monsoon sets in.
  • But among the two seasons, the period from October-November, is said to produce more devastating cyclonic storms, primarily due to the cooling of the ocean temperatures, which creates instability in the upper air column.
  • But of late, it is seen that the season is extending to December, which is a clear indication of climate change, due to global warming.
  • Climate researchers point out that it is not only the frequency that has increased in the last 30 years, but also the intensity of the tropical storms to a great extent.
  • But the most devastating in the recent times was Hudhud, when it made its landfall with wind speed touching 215 to 240 kmph in Visakhapatnam on October 12, 2014.
  • Over the last 100 years, the surface temperature of the oceans has increased by about 10 C, which is a sign of global warming.
  • Higher the ocean surface temperature, more will be the evaporation, more will be the moisture in the air, which will lead to low pressure and increase in instability.
  • These collaborated with other factors such as vertical wind shear, initial vortex, relative humidity and degree of convective instability, will trigger a tropical cyclone.
  • North Indian Ocean is the most potential source for formation cyclonic storms, primarily it is because that the ocean is a landlocked one
  • It has two arms — the Bay of Bengal and the Arabian Sea.
  • Compared to the both, the recurrence of tropical cyclones is more over Bay of Bengal.
  • This is primarily because the Arabian Sea temperature is relatively cooler and Bay is warmer.
  • The water stratification is higher in the Bay of Bengal.
  • The flow of fresh river water and rain water is much higher in the Bay of Bengal and due to which the vertical mixing of cooler lower water with the warmer surface water is weaker.
  • And due to weak mixing, the top surface remains warmer and the upper air column becomes buoyant.
  • With the supply of moisture, the atmosphere becomes unstable, which leads to formation of such systems.