A delayed monsoon, however, has no correlation with the quantity and distribution of rainfall in the June-September season as well as the pace of its progress over remaining parts of the country.
Announcing the onset of southwest monsoon over Kerala, the India Meteorological Department (IMD) Thursday said conditions were favourable for further advance of the rain-bearing system into the remaining parts of Kerala, some more parts of Tamil Nadu, some parts of Karnataka and parts of the northeastern states during the next 48 hours.
“The formation of a low-pressure system in the Arabian Sea, which subsequently intensified into the very severe cyclone ‘Biparjoy’, delayed the onset of the monsoon over Kerala as it took moisture away from the region,” IMD chief Mrutyunjay Mohapatra told TOI.
The Met department announced the monsoon’s onset after the rainfall and cloud formations met all the conditions including depth of westerly winds over southeast Arabian sea. Besides, there has been widespread rainfall over Kerala during the past 24 hours — yet another condition to be considered for announcement of the onset.
Southwest monsoon has set in over Kerala today: IMD
The IMD had on May 16 predicted the onset of monsoon over Kerala on June 4 with a model error of ± 4 days. So, the arrival this year is within the forecast range. Summer monsoon normally sets in over Kerala on June 1 with a standard deviation of about seven days even as it arrives over Andaman & Nicobar Islands around two weeks early.
The IMD has already predicted “normal” monsoon this year, despite evolving El Nino conditions (unusual warming of surface waters in eastern Pacific Ocean) that is generally linked to weak monsoon rains.
The past data shows that the years 2016 and and 2019 reported “normal” and “above normal” rainfall, respectively, despite making a delayed onset by seven days. Even distribution of rainfall was good in both these years, helping foodgrain output to reach the then record level of 275 million tonnes in 2016 and 297 million tonnes in 2019.
Banking on the forecast of a “normal” monsoon this year, the agriculture ministry has set a target of 332 million tonnes of foodgrain output in 2023-24 crop year.
The IMD has been issuing operational forecasts for the onset date over Kerala since 2005. Records show that the Met department’s forecasts of the date of monsoon onset over Kerala during the past 18 years (2005-2022) were proved to be correct except in 2015. It has been using an indigenously developed state-of-the-art statistical model with a model error of ± 4 days for the purpose of making a monsoon onset forecast.