"The southwest monsoon has set in over Kerala today (Saturday)," said L.S. Rathore, director general of the IMD.
"The rainfall monitoring stations for the monsoon's onset over Kerala have reported fairly widespread to widespread rainfall in the last 48 hours," he said.
According to IMD, the monsoon has covered all of Kerala, some parts of coastal and south interior Karnataka, most parts of Tamil Nadu and some more parts of southwest and westcentral Bay of Bengal.
"Conditions are favourable for further advance of monsoon into some more parts of the central Arabian Sea and Karnataka, remaining parts of Tamil Nadu, some parts of south Andhra Pradesh and some more parts of Bay of Bengal during next 48 hours," Rathore said.
The southwest monsoon normally sets in over Kerala around June 1, and advances northwards, usually in surges, covering the entire country by mid-July.
Spotted: Virat Kohli, Anushka Sharma and other celebs at Mumbai airport
Photos: Salman Khan's 'special friend' Iulia Vantur at a song launch
Photos: Hrithik Roshan, Anushka Sharma, other celebs dazzle at event
In Pictures: Sex scandals involving Indian politicians
Photos: Abhishek Bachchan and Farah Khan at Boman Irani's birthday bash