Cyclone development: Bay of Bengal and Arabian Sea

  • Cyclones are known to originate in both the Bay of Bengal and the Arabian Sea sides of the northern Indian Ocean but the Bay of Bengal side witnesses four times more cyclones than the Arabian Sea side on average.
  • Following are reasons:
    • The relatively colder waters of the Arabian Sea are not conducive to the formation and intensification of cyclones.
    • The eastern coast of India receives cyclones that form not just in the Bay of Bengal, mostly around the Andaman Sea near the Andaman and Nicobar Islands, but also those travelling from the Pacific Ocean, where the frequency of ‘typhoons’, as these are called there, is quite high (about 35 % of the global annual average).
    • Most of these cyclones weaken considerably after encountering a big landmass. Therefore, these do not travel to the Arabian Sea side.
    • The western coast of India thus witnesses only those cyclones that originate locally or the ones, like Ockhi, that travel from the Indian Ocean near Sri Lanka.


Naming the Cyclone

  • Cyclones, hurricanes and typhoons are usually named for the benefit of easy communication between forecasters and the public.
  • The naming of cyclones was started in 2000 by the World Meteorological Organization (WMO) and the United National Economic and Social Commission for Asia and the Pacific (ESCAP).
  • Nine regions are responsible for the nomenclature namely — North Atlantic, South Atlantic, Eastern North Pacific, Central North Pacific, Southern Pacific, Western North Pacific, North Indian Ocean, South West Indian Ocean.
  • Each regional body has its own rules in naming cyclones. In most regions pre-determined alphabetic lists of alternating male and female names are used.
  • Cyclones originating in the North Indian Ocean basin between 45°E-100°E are named by the Indian Meteorological Department (IMD).
  • South Asian countries surrounded by the Indian Ocean such as Bangladesh, India, Maldives, Myanmar, Oman, Pakistan, Sri Lanka and Thailand had submitted eight names each (in above sequence). These 64 names are used in sequence and the names of significant tropical cyclones are retired.
  • The first tropical cyclone was named ‘Onil’ by Bangladesh in 2004. Ockhi has been named by Bangladesh. In Bengali, ‘Ockhi’ means eye. The next cyclone has already been named by India as ‘Sagar’.


Ockhi Cyclone

  • Ockhi originated near the south-western coast of Sri Lanka, and travelled very near the southern-most tip of the Indian mainland, along the coasts of Tamil Nadu and Kerala, towards the Lakshadweep islands, where it was at its most powerful.
  • It weakened considerably after that and continued further, taking a north-easterly turn towards the Maharashtra and Gujarat coastlines —cyclones in this area are not a common phenomenon.
  • Ockhi was described as a ‘very severe cyclonic storm’, the third strongest category according to the definitions used by the India Meteorological Department (IMD). Cyclones are categorised by the maximum wind speed they generate.