From low pressure area to very severe cyclonic storm: How IMD tracked Vardah

A small dot marked on the screens of weathermen at the IMD signalled to them that a very severe cyclonic storm was building up in the South Andaman Sea, nine days ahead of the landfall of 'Vardah' that ravaged coastal Tamil Nadu and Andhra Pradesh.

The dot on the screen signified pressure movement over a particular area, which had the potential of snowballing into a cyclone.

Weathermen at the IMD's Regional Specialised Meteorological Centre (RSMC) here, who monitor any slight change in weather patterns around India especially in the cyclone-prone Bay of Bengal, realised on December 3 that a low pressure area was being formed near the South Andaman Sea.

The pressure belt had traversed from the South China Sea, flowing over Thailand and Vietnam which had reduced its speed considerably due to its contact with the land.

"So, as soon as it reached the South Andman Sea, it again got traction. The warm water in the Indian Ocean and the South Andaman Sea gave it momentum and then started the process of forming a low pressure area.

"We realised that there was an anti-clockwise pattern, the wind speed around it had increased more than other parts of the sea," said M Mohapatra, Additional Director General (Services) with the India Meteorological Department, who has been in the business of forecasting cyclones. He was also the head of Cyclone Warning Division during Phailin and Hudhud.

September to December is also the time when weathermen at the Cyclone Warning Division of the IMD avoid taking leaves. For them, this is cyclone season.

Realising that the low pressure area was developing into something stronger, the officials started gathering more data, pressing into service IMD's two doppler radars at Chennai and Machilipatnam, coastal automatic weather stations and manned observatories, besides its buoys in the sea.

Satellite images from INSAT-3D and Met services of Thailand and Malaysia were also used.