Chennai is battling worst rains in nearly 100 years, breaking century-old rainfall records. Heavy to extremely heavy rains have been lashing at the south city for quite some time now, triggering floods. Heavy to very heavy rain is still expected to batter Chennai and adjoining cities for next 48 hours.
But what is causing this incessant rain over the southern state and its coastal city?
At present, Chennai is in the peak period of the Northeast Monsoon, which is from November 15 till December 15. During this period, we witness most ferocious Monsoon systems developing in the Bay of Bengal that affect the Indian coast.
However this year, this is not the reason behind the torrential rains. According to Skymet Meteorology Division in India, these extremely heavy spells of rain have a strong relation with El-Nino.
El-Nino in 2015 is the strongest on the record, which has the worst impact on Indian weather.
Impact of El-Nino
El-Nino is an oceanic-atmospheric phenomenon where sea surface temperatures of East Pacific Ocean warm up, while the Indian Ocean and the Bay of Bengal have relatively cool temperatures. For the development of any cyclone or strong weather system, we require warm sea surface temperatures (SST).
As a result, central Bay of Bengal did not witness any weather systems this year on account of cooler SST. However, positive Indian Ocean Dipole kept SST warm in South Bay of Bengal and hence, we saw three strong weather systems developing in South Andaman Sea.
These weather systems moved in the west-northwest direction towards Sri Lanka and Tamil Nadu, triggering heavy to very heavy rain over Tamil Nadu including Chennai.
Normally during October and November, cyclones forming in Central Bay of Bengal move in northwest direction towards Andhra Pradesh and Odisha coast. Under these circumstances, major chunk of rain is recorded over Andhra Pardesh, Odisha and West Bengal.
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