The monsoon is likely to break over the Kerala coast on May 24, a week before it is normally due on June 1, the met office said on Monday.
"The forecast model suggests that the monsoon onset over Kerala is likely to be on May 24, with an error of three days," an India Meteorological Department (IMD) official said.
The IMD uses six predictors to make its forecast, including minimum temperature over northwest India and pre-monsoon rainfall over the southern peninsula.
The southwest monsoon has already set in over the South Andaman Sea on May 10 almost a week earlier than its normal date.
The monsoon usually covers the whole country by July 15. It arrives over Mumbai by June 10 and over Delhi by June 29.
However, an IMD official said there is no relation between the monsoon over Kerala and the monsoon rains over the country as a whole.
"An early onset over Kerala does not suggest an early monsoon onset over the interior parts of the country, especially north India," he explained.
During the last 50 years, the earliest monsoon set over Kerala was on May 14 in 1960 and the most delayed onset was on June 18 in 1972.