The southwest monsoon is expected to set in over Kerala around June 4, said the India Meteorological Department on Tuesday.The weather agency had earlier predicted that the monsoon would arrive in Kerala by May 26. However, it acknowledged on May 29 that the monsoon was unlikely to set in over the state within the four-day window around that date, The Hindu reported.“Conditions are favourable for further advance of southwest monsoon into some more parts of southwest and southeast Arabian Sea, Lakshadweep Islands, some parts of Kerala and Tamil Nadu, some more parts of southwest, westcentral, eastcentral and northeast Bay of Bengal, and remaining parts of southeast Bay of Bengal around 4th June,” the IMD said on Tuesday. The agency added that isolated heavy to very heavy rainfall between 7 and 20 centimetres was very likely over Kerala in the next six to seven days. Isolated parts of Tamil Nadu and Karnataka are also expected to receive heavy rains during this period.In 2025, the southwest monsoon set in over Kerala on May 24, which was its earliest arrival since 2009.In April, the IMD predicted below-normal rainfall of 92% during this year’s southwest monsoon season. This was the first time in 11 years that a shortfall in rainfall was forecast.On May 29, the agency revised its prediction downwards to 90% of the long-period average. The long- period average is the measure of the mean rainfall during the four-month monsoon season over the last 50 years.If a monsoon season records rainfall below 90% of the long-period average, the IMD classifies it as “deficient”.The expected shortfall this year is primarily due to the likely development of El Niño conditions in the equatorial Pacific Ocean after June, the weather agency said.The El Niño weather phenomenon involves the warming of ocean surface temperatures in the eastern and central Pacific. It typically occurs every few years and has been linked to reduced monsoon rainfall over India.The IMD said that the impact of El Niño is expected to become more pronounced in the latter half of the monsoon season, particularly in August and September, due to a lag between its development and its influence on Indian weather patterns.Written by Neerad Pandharipande. Edited by Sneha.