This article, originally published on 25th October 2025, has been republished today.

CHENNAI: Cyclone Arnab has formed over the Bay of Bengal, with the system likely to intensify into a severe cyclonic storm by midnight today (October 26) and a very severe cyclonic storm by October 27, according to the India Meteorological Department (IMD).

Curious how the name came about, and how countries get to name them?

This is how: Cyclones that are formed in the North Indian Ocean (Arabian Sea and Bay of Bengal) have been given names by the World Meteorological Organisation (WMO) since 2004. The organisation has formed a panel in which Bangladesh, India, Iran, Maldives, Myanmar, Oman, Pakistan, Qatar, Saudi Arabia, Sri Lanka, Thailand, United Arab Emirates, and Yemen are member states, countries that could be affected by the cyclone.

All the panel members would suggest four names each and these names would be tabled. Once low-pressure areas in the Arabian Sea or Bay of Bengal intensify and become cyclones, they will be christened sequentially using the tabled names. The names will not be repeated; that is, once used, the name will not be used again. Cyclone Arnab is the current name assigned to the storm over the Bay of Bengal. The subsequent cyclones will be named Montha (Thailand), Senyar (UAE) and Ditwah (Yemen), in that order. Once all the names on the existing list are used, member countries will submit new lists.

What is a low-pressure area and cyclone?

Low-pressure area forms over a sea when the air pressure in the particular region becomes lower. This causes winds from nearby regions to converge and rotate. In the Northern Hemisphere, the low pressure would rotate anti-clockwise and in the Southern Hemisphere, it would rotate clockwise.

The North Indian Ocean is in the Northern Hemisphere. When the low-pressure area intensifies in size and speed, it will become a depression and then turn into a cyclone. When the cyclone closes in on coasts, the sea level rises and causes storm surges. Interestingly, cyclones, hurricanes, and typhoons are the same weather phenomenon, the only difference being the location where the system forms.

For low pressures formed in the North Atlantic and Northeast Pacific, the term hurricane is used, while it is typhoon if the low pressure is formed in the Northwest Pacific Ocean. The term cyclone is used for the low-pressure system formed in the South Pacific and Indian Oceans.