Thiruvananthapuram: Vehicles wade through a waterlogged road after rainfall, in Thiruvananthapuram, Kerala, Saturday, May 30, 2026. (PTI Photo)The southwest monsoon is expected to onset over Kerala around June 4, the India Meteorological Department (IMD) said on Tuesday.Typically, monsoon arrives in Kerala around June 1, which marks the beginning of the southwest monsoon season (June-September).“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 around June 4,” the IMD said in its daily forecast.It added that the monsoon will also advance in some more parts of the southwest, west-central, east-central, and northeast Bay of Bengal, and the remaining parts of the southeast Bay of Bengal around this date.Also Read | IMD forecast today: Heavy rainfall, hailstorms, and duststorms to hit several statesThe IMD had earlier said the monsoon onset over Kerala would take place on May 26. However, it got delayed, and the department, on May 29, stated that the onset could happen in the following week.Last week, the department in its revised forecast for the rainfall during the season said it would be below normal.The IMD stated that India is expected to see 90 per cent of the long-period average (LPA) this year.Story continues below this adLPA refers to the rainfall recorded over a particular region for a given interval, such as a month or a season, averaged over a long period of time, typically 30 to 50 years.The LPA of seasonal rainfall over the country as a whole, based on data from 1971 to 2020, is 87 cm.Also Read | Monsoon advances further; heavy rain alert for Northeast, South this weekIf the monsoon season sees less than 90 per cent of LPA rainfall, the IMD classifies it as “deficient”.One reason for the below-normal rainfall could be the emergence of El-Nino conditions, which lead to less rain during the monsoon in the country.Story continues below this adCurrently, neutral El Nino-Southern Oscillation conditions are transitioning towards El-Nino conditions over the equatorial Pacific region.The IMD said El-Nino conditions are likely to be weak in June, and moderate to strong in September.