The India Meteorological Department (IMD) on Wednesday said that monsoon will hit Kerala coast on May 31, which is a day earlier than its normal schedule day of June 1 in the mainland. IMD also said the southwest monsoon is very likely to advance into South Andaman Sea, some parts of Southeast Bay of Bengal and Nicobar Islands around May 19.

“This year, the southwest monsoon is likely to set over Kerala on May 31, with a model error of ± 4 days,” IMD said in a statement late evening.

The weather bureau also said its “operational forecasts” (inclusive of error margin) of the date of monsoon onset over Kerala during the past 19 years (2005-2023) were proved to be correct, except in 2015.

“This is not early. It’s near normal date as the normal date for onset of monsoon over Kerala is June 1,” IMD’s Director General Mrutyunjay Mohapatra said. The weather bureau has predicted this year’s rainfall to be above-normal, quantitatively 106 per cent of its long period average of 87 cm with a model error of (+/-) 5 per cent during the June-September monsoon season. According to IMD, rainfall between 105 and 110 per cent of LPA is considered “above normal” and between 96-104 is categorised as “normal”. Monsoon was above normal in 2019, 2020 and 2022.

Six predictors used

“Advance of the monsoon over Indian mainland is marked by monsoon onset over Kerala and is an important indicator characterising the transition from hot and dry season to a rainy season,” IMD said. As the monsoon progresses northward, relief from scorching summer temperatures is experienced over the areas. IMD has been issuing operational forecasts for the date of monsoon onset over Kerala from 2005 onwards, based on a statistical model.

The six predictors used in the models are -- 1) Minimum Temperatures over north-west India, 2) Pre-monsoon rainfall peak over south Peninsula, 3) Outgoing long wave radiation (OLR) over south China Sea, 4) Lower tropospheric zonal wind over equatorial south-east Indian Ocean, 5) Outgoing OLR over south-west Pacific Ocean and 6) Upper tropospheric zonal wind over equatorial north-east Indian Ocean, IMD said.

Year Actual Forecast

2019 June 8 June 6

2020 June 1 June 5

2021 June 3 May 31

2022 May 29 May 27

2023 June 8 June 4