Thiruvananthapuram/New Delhi: The Southwest Monsoon has set in over Kerala on Sunday, three days ahead of its usual date of June 1, marking the start of the four-month rainy season that is crucial for India's farm-based economy.

Kerala has been receiving rainfall since Saturday and 10 out of the 14 weather monitoring stations in the state have received more than 2.5 mm rains, thus fulfilling the criteria for the onset of monsoon, the India Meteorological Department (IMD) said.

Southwest monsoon has set in over Kerala on Sunday, May 29, against the normal date of onset of June 1, IMD Director General Mrutyunjay Mohapatra said.

However, while the monsoon has advanced over Kerala and parts of Tamil Nadu, the Bay of Bengal arm of the weather system was sluggish as it continued to linger just above the Andaman islands.

The Extended Range Forecast issued by the IMD has suggested that the progress of the monsoon over Karnataka, Ga and entire north-east India could be slow.

Earlier, the IMD had forecast onset over Kerala on May 27 with help from the remnants of Cyclone Asani, which struck the Bay of Bengal a fortnight ago. The forecast had a model error of four days.

However, the influence of the remnant weather systems, that lingered over the southern peninsula, petered out, dashing the forecast of an early onset over Kerala and swift progress towards the north.

The other criteria for declaring the onset of monsoon over Kerala are depth of westerly winds extending up to 4.5 km above sea level, strong westerly winds and outgoing long radiation (OLR) less than 200 W/M2 over the region.

All conditions for the onset of monsoon over Kerala have been satisfied on Sunday, May 29, 2022, the weather office said in a statement on Sunday.

It noted that cloudiness had increased over the southeast Arabian Sea and adjoining areas of Kerala, while the OLR was 189 W/M2 and westerly winds were blowing at a speed of 25-25 km per hour.

Conditions were favourable for further advance of southwest monsoon into some parts of central Arabian Sea, remaining parts of Kerala, some more parts of Tamil Nadu, Karnataka, during next three to four days.

The IMD had declared the onset of monsoon over Andaman & Nicobar Islands on May 16 and had forecast rapid advance over peninsular India towards the end of May.

The ERF shows that the rainfall activity will remain normal to below normal till about June 8 along these areas.

All southern states/UTs have received above-normal rainfall since March to May 28: Karnataka (136 per cent), Lakshadweep (112 per cent), Kerala (98 per cent), Puducherry (87 per cent) and Andhra Pradesh (34 per cent).

Only Telangana (minus 28 per cent) remains rain deficient during the pre-monsoon season.