New Delhi: A deadly combination of two low-pressure areas in the Bay of Bengal, a cyclonic circulation and an intensifying monsoon in the southeast Arabian Sea, led to heavy rains in Kerala this month, experts said.
The coastal state along the Western Ghats witnessed unprecedented rainfall which claimed more than 223 lives, forced over 10 lakh people out of their homes and destroyed property worth several thousand crores.
While June and July recorded 15 per cent and 18 per cent more rainfall than normal respectively in the state, August 1-19 recorded 164 per cent excess rainfall, the India Meteorological Department (IMD) said.
G P Sharma, president (Meteorology), Skymet said troughs along the Western Ghats from Konkan to Kerala, low-pressure areas arising in the Bay of Bengal, Somali jet phenomenon played an important role in bringing rains along the Western Ghats.
Somali jet streams are winds that originate near Madagascar, recurve, and come towards the Western Ghats. The combination of all these factors brought unprecedented rainfall in the state.
"The monsoon was already active over the state and there was an off-shore trough from Konkan Goa to Kerala," said Mahaesh Palwat, vice-president (Meteorology and Climate Change ) at the Skymet, a private weather forecasting agency. Plus, there was a cyclonic circulation over the southeast Arabian Sea that was influencing Kerala and south coastal Karnataka, he said.
To add to it, there were two low-pressure areas formed near the Odisha coast on August 7 and 13. Although the low-pressure area brought a lot of rains to central India, it attracted winds from the Arabian Sea.
"These low-pressure areas pulled the easterlies from the Arabian Sea and collided over the Western Ghats resulting in the formation of clouds over the state that brought heavy rains," Mritunjay Mohapatra, Additional Director General, IMD.
Coming together of several weather patterns often causes large scale destruction and loss of lives and property. For instance, a cyclonic circulation over Haryana was the trigger for the deadly dust storm that swept parts of Rajasthan and Uttar Pradesh in the first week of May, killing over 120 people.
There were primarily four reasons that led to the thunderstorm -- excessive heating when temperatures crossed over 48 degrees at several places in the north Indian plains, availability of moisture from a Western Disturbance and easterlies from the Bay of Bengal, instability in the atmosphere and a trigger for the storm.