Tornadoes, like the one in Bengal, can be seen ahead of cyclone: Experts
Even before the very severe cyclone Yaas could hit the Odisha – West Bengal coast on Wednesday morning, videos of a tornado swirling over villages and the river Ganga in south Bengal went viral on social media.
Chief minister Mamata Banerjee said at least two persons were electrocuted when the mini tornado hit parts of Hooghly and North 24 Parganas, and around 40 houses were damaged.
While the incident took the locals of Bandel, Chinsurah, Halisaha in the two districts by surprise, meteorological experts said tornadoes can develop before an approaching cyclone or a major thunderstorm.
“When a cyclone approaches, such vortex develops because of the difference in wind speed in the upper air and the ground level, known as vertical wind-shear. This is, however, not a full tornado, It is a mini-tornado,” said Sanjib Banerjee, deputy director general of India Meteorological Department’s regional office in Kolkata.
Such mini tornadoes have been seen earlier in the district of Murshidabad in west Bengal and also in Odisha experts said. Even though it is rare, but thunderstorm activity occurs when a cyclone approaches.
“They can happen when a cyclone or a thunderstorm approaches. Just like a pilot car moves ahead of a VIP convoy, these mini tornadoes act like a pilot of the cyclone, occurring before a cyclone comes,” said KJ Ramesh, former head of the IMD.
If the tornado passes over a water body or a river, it starts lifting the water. There were examples from Odisha where a mini tornado had emptied an entire pond by lifting the water.
“A tornado is basically a column of air rotating violently that extends from a thunderstorm to the ground. It tears and lifts everything in its path,” said a meteorological department official.
Ramesh recalled seeing such a mini tornado ahead of a thunderstorm in Delhi in which an entire bus was lifted in the air by the vortex in the early 70’s.
“Just like a cyclone and a thunderstorm, a tornado too needs heat and moisture to develop,” said RK Jenamani, senior scientist of IMD.