MUMBAI: The southwest monsoon arrived in Maharashtra on Sunday, making it the earliest onset of the annual rainfall season over the state in 35 years, the India Meteorological Department said.

The southwest monsoon is expected to advance to Mumbai and some other parts over the next three days, the IMD added.

In 1990, southwest monsoon made onset over Maharashtra on May 20, IMD scientist Sushma Nair said.

The monsoon advanced into some more parts of the Arabian Sea, Karnataka, entire Goa, parts of Maharashtra, north Bay of Bengal, and parts of Mizoram, parts of Manipur and Nagaland on Sunday, the IMD said.

The northern limit of monsoon passes through Devgad, Belagavi, Haveri, Mandya, Dharmapuri, Chennai, Aizawl and Kohima, it said.

"Conditions are favourable for further advance into some more parts of central Arabian Sea, more parts of Maharashtra including Mumbai, Karnataka including Bengaluru, some parts of Andhra Pradesh, remaining parts of Tamil Nadu, more parts of west-central and North Bay of Bengal and some more parts of North Eastern states during next three days," the IMD said.

In Maharashtra, the coastal Konkan stretch and Mumbai have been witnessing heavy pre-monsoon rains over the last two days.

The southwest monsoon hit Kerala on Saturday, marking its earliest arrival over the Indian mainland since 2009 when it had reached the southern state on May 23.

Normally, the southwest monsoon marks its onset over Kerala by June 1 and covers the entire country by July 8. It starts retreating from northwest India around September 17 and withdraws completely by October 15.

It usually reaches Maharashtra around June 7 and Mumbai on June 11.

M Rajeevan, a monsoon expert and former secretary of the Ministry of Earth Sciences, said early onset and covering a large area on the first day is not uncommon.

"In 1971, monsoon at the time of onset covered a larger area in Karnataka and parts of Maharashtra. Present active monsoon conditions will continue at least till June 2 and will help to advance monsoon into Maharashtra and eastern parts of the country," Rajeevan said.