IAS Gyan

Daily News Analysis

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

30th November, 2020 Geography

The story so far: Cyclone Nivar, 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.
  • With relatively fewer lives were lost compared to the havoc wreaked by Amphan in West Bengal in May.
  • Nivar was 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 IMD also collaborates with 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
  • 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.

How has disaster warning changed?

  • For accuracy IMD replaced its present age-old radar with the latest X-band radar. IMD begins impact-based forecast
  • 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.
  • 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.