It had on May 14 predicted it to be around May 31 with model error of +/- 4 days. The normal onset date of the southwest monsoon falls on June 1 with a standard deviation of 7 days.
“As per the latest meteorological indications, the southwesterly winds could strengthen further gradually from June 1, resulting in likely enhancement in rainfall activity over Kerala. Hence, the monsoon onset over Kerala is likely to take place by June 3,” said the country’s national weather forecaster in its latest update on Sunday.
The IMD has been issuing operational forecasts for the date of monsoon onset over Kerala from 2005 onwards. It claimed that the operational forecasts of the date of monsoon onset over Kerala during the past 16 years (2005-2020) were proved to be correct except in 2015.
The IMD had last month predicted overall ‘normal’ monsoon rainfall in the country during the June-September period. It had said the monsoon seasonal rainfall was likely to be 98 per cent of the Long Period Average (LPA) with a model error of +/- 5 per cent. The LPA of the season rainfall over the country as a whole for the period 1961-2010 is 88 cm. The rainfall to an extent of 96-104 per cent of the LPA is considered ‘normal’.
The country’s national weather forecaster had released new normal dates of onset and withdrawal of southwest monsoon based on recent data on April 15 last year. The normal dates of onset were revised based on data during 1961-2019 and normal dates of withdrawal were revised based on data during 1971-2019.
As per the new normal, the monsoon sets over Kerala around June 1, nearly the same as the earlier normal date and covers the entire country one week before the previous normal. However, monsoon withdrawal from northwest India is delayed by more than 2 weeks compared to the earlier normal date (September 1).
Monsoon retreats from most parts of the country except south Peninsula and some parts of neighbouring central India by October 15, coinciding with the earlier normal, and subsequently northeast monsoon gets established over south Peninsula.