How are cyclones forecast, and how difficult was it to track Cyclone Nivar’s progress?

Cyclone Nivar, that barrelled through Tamil Nadu and brought copious rain in its wake, 

was the third major cyclone to land on India’s coast this year, besides Amphan and Nisarga. 

The Nivar storm originated in the Bay of Bengal and whipped up windspeeds close to 125-

145 kmph, blowing away roofs and felling standing crop. However, relatively fewer lives 

were lost compared to the havoc wreaked by Amphan in West Bengal in May. What aided 

relief operations in the anticipation of Nivar was that it largely conformed to forecasts 

issued by the India Meteorological Department (IMD). 

How are cyclones forecast? 

Over the years, India’s ability to track the formation of cyclones has improved significantly. 

There is a network of 12 doppler weather radars (DWR) along India’s coast if one were to 

begin counting from Kolkata and trawl up to Mumbai — there are 27 in all in the country. 

Depending on where a storm is forming, these radars send pulses of radio waves to gauge 

the size as well as the speed at which water droplets are moving. The earlier generation of 

radars was unable to track such progress in real time, but with DWRs, now the base 

standard of weather radars, it is usually possible to detect a potential storm at least four-

five days in advance. The IMD also collaborates with similar international networks, such 

as the Japan Meteorological Agency, the U.S. National Hurricane Center, and the U.S. Central 

Pacific Hurricane Center, and these bodies constantly send warnings and forecasts about 

changes in the ocean weather. The near ubiquity of ocean-buoys that track changes in 

ocean sea surface temperatures as well as dedicated meteorological satellites improve the 

odds of early detection. 

How difficult was it to track Nivar’s progress?

Nivar was the second tropical cyclone that formed around India and made landfall this 

week. Cyclone Gati, which originated in the Arabian Sea and intensified into a ‘very severe 

cyclonic storm’, made its way towards Africa and made landfall in Somalia on November 

22. However around then, another system emerged in the Bay of Bengal, that eventually 

morphed into a cyclonic storm by November 24. The IMD’s initial forecasts said it would at 

most be a ‘severe cyclonic storm’, but it then upgraded it to the same league as Gati, i.e, a 

‘very severe cyclonic storm’. The IMD follows a five-stage classification for cyclones, with 

the lowest a ‘cyclonic storm’ generating wind speeds of 62-87 kmph, and the highest a 

‘super cyclonic storm’, generating winds over 222 kmph.

April-June and October-December are India’s cyclone seasons. The arriving monsoon, as 

well as its retreat, stir up the surrounding seas and generate cyclones. Though the Bay of 

Bengal is three times more likely to generate cyclones, the ones that originate in the 

Arabian Sea are trickier, as the cyclone, while ostensibly moving away from India’s western

coast, can suddenly ‘recurve’ and move back in. There are also fewer radars along India’s 

west coast than the eastern coast, and all these reasons make the Bay of Bengal cyclones 

more tractable. In this context, Nivar, because it conformed to a fairly predictable trajectory 

and was not super cyclonic in intensity, gave State administrations in Puducherry, Tamil 

Nadu and Andhra Pradesh time to prepare, and was far less damaging than Amphan. 

However, the cyclone season is not yet over and more systems are likely to form in the 

coming weeks, according to the IMD. 

How has disaster warning changed? 

Forecasts, on their own, are important, but they cannot override the importance of 

preparedness by State agencies. The formation of cyclones is preceded by ‘depressions’, 

and they are often the first warnings. Not all depressions become cyclones, but many 

coastal States — especially those with a history of being battered — begin organising 

shelters and evacuation of coastal residents. Sea pockets, where cyclones form, are also 

places that drive schools of fish and lure fisherfolk. While meteorological agencies give 

advisories on where fish-catches are likely, they suspend such advisories during storm 

formation to dissuade fishermen from venturing out. The ubiquity of mobile 

communication makes it much easier to quickly give warnings. The IMD also issues flood 

forecast maps, in collaboration with urban bodies that forecast which pockets in a city are 

likely to be flooded and where crop damage is likely to be maximum.