New Delhi, June 1 : The Southwest Monsoon arrived in Kerala on Monday as predicted by the India Meteorological Department bringing heavy rains to several parts in the state and marking the commencement of the four-month long rainfall season in the country. "Southwest Monsoon has set in over Kerala today, coinciding with its normal date," the IMD stated. Advance of the southwest monsoon over Indian mainland is marked by monsoon onset over Kerala and is an important indicator characterizing the transition from hot and dry season to a rainy season. Speaking to IANS, IMD Director General Mrutyunjay Mohapatra said, "Monsoon has arrived. There has been heavy to very heavy rainfall at several places over Kerala. There has also been a persistent increase in cloudiness and strong winds. This is in line with the predictions." Meteorological conditions which led to onset of monsoon are -- widespread rainfall during the past two days, strengthening and deepening of westerly winds upto 4.5 kilometre over the Arabian Sea and persistent cloudiness. The Met department has issued heavy rainfall warnings for Kerala. "Thunderstorm with lightning and wind speed reaching 40 kmph in gusts accompanied by moderate rainfall is very likely to occur in Thiruvananthapuram, Kollam, Ernakulam, Thrissur, Kozhikode, Malappuram, Kasaragod and Kannur." The IMD had earlier said that conditions were favourable for the onset of the monsoon over Kerala on June 1 due to the formation of Cyclone 'Nisarga' over Arabian Sea. This was a revision of its earlier onset forecast of June 5. In 2015, it hit the coastal state on June 5; in 2016 it made an onset on June 8; it was May 30 in 2017; May 29 in 2018 and June 8 in 2019. Monsoon rains are critical for farmers in India as the majority of the country's net-sown area does not have any form of irrigation. Farmers wait for the rains to begin for sowing. On April 15, Madhavan Rajeevan, Ministry of Earth Sciences Secretary had forecast that monsoon rains this year were likely to be normal at 100 per cent with a model error of 5 per cent. The weather bureau is slated to issue the second stage Long Range Forecast (LRF) for South-West Monsoon Season (June - September) rainfall later in the day. The monsoon season from June to September accounts for 75 per cent of rainfall in the country. /IANS