"Southwest Monsoon has set in over Kerala on June 5 against the normal date of June 1," IMD said in a statement.
"The rainfall over Kerala has been fairly widespread to widespread for the last 48 hours. Out of the 14 rainfall monitoring stations for monsoon onset over Kerala, more than 70% of stations have reported rainfall higher than 2.5 mm for last consecutive two days," IMD said in its statement.
"Monsoon has further advanced into entire south Arabian Sea, some parts of Central Arabian Sea, entire Lakshadweep area and Kerala, some parts of Coastal & South Interior Karnataka and Tamil Nadu, remaining parts of southeast Bay of Bengal and some parts of central & northeast Bay of Bengal," the statement added.
According to IMD, "Conditions are favourable for further advance of southwest Monsoon into some more parts of central Arabian Sea, Karnataka; remaining parts of Tamil Nadu, some parts of Rayalaseema and Coastal Andhra Pradesh, some more parts of central & north Bay of Bengal and southern parts of northeastern states during next 48 hours."
Dark clouds formed at many places in Kerala since Wednesday evening, suggesting possible rains.
Fishermen have been warned about winds blowing 45 to 55 km an hour on the coast. The IMD earlier said that the southwest monsoon would set over Kerala on May 30, with a model error of plus or minus four days.