The monsoon is "very likely" to hit Kerala by June 9, the India Meteorological Department (IMD) on Tuesday said.

It said that the southwest monsoon has furthered advanced into some parts of south Arabian Sea, Maldives, Comorin area and some parts of southwest Bay of Bengal.

"In view of strengthening of cross equatorial flow and deepening of westerlies over south Arabian sea and development of feeble off-shore trough along Karnataka-Kerala coast, onset over Kerala is very likely by June 9," the IMD said in its latest bulletin.

The IMD had yesterday said that conditions continue to remain favourable for the onset of southwest monsoon over Kerala in next 48 hours, marking the start of rainy season in the country.

The IMD had earlier said that monsoon should hit the Kerala coast on June 7, with an error margin of plus or minus four days.

Several parts of Kerala are already witnessing heavy rains.

Rains also lashed many parts of Tamil Nadu in the last 24 hours ending at 0830 hours today, the regional weather office said.

Summer rains, accompanied with lightning and thunder, were witnessed in many parts of the state including Chennai, it said, adding, Sembarambakkam recorded the highest rainfall of five cm, followed by Chennai at four cm.

The weather office forecast rain at a few places in South Tamil Nadu and over one or two places in the northern parts of the state for the next 48 hours.

Thunderstorms were likely in Chennai during the period, it said.

The IMD has also made a forecast of "heavy" to "very heavy" rain at isolated places over coastal Karnataka, Kerala, Lakshadweep, sub-Himalayan West Bengal, Sikkim and "heavy" rains at isolated places over Arunachal Pradesh, Assam, Meghalaya, Rayalseema region of Andhra Pradesh and south interior Karnataka.

However, there is going to be "no significant" change in maximum temperatures in northwest India for the next 2-3 days which is reeling under intense heat.

Heat wave to severe heat wave conditions are very likely at a few places over West Rajasthan, at isolated places over east Rajasthan and west Madhya Pradesh. Heat wave is likely at isolated places over Haryana, Chandigarh, Delhi and Gujarat.