The southwest monsoon has reached Kerala, the India Meteorological Department (IMD) said on Sunday. While this is three days before the usual onset date of June 1, it is two days later than what the IMD had earlier forecast on May 13.
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Rainfall is not the only criteria that the IMD relies on to declare the monsoon’s onset. Windspeeds of a minimum strength and depth in the atmosphere, the Outgoing Longwave Radiation — a measure of cloudiness — and rainfall appearing to be consistent and well distributed over Kerala, are important criteria.
Until Saturday, most of these parameters — except sufficient rainfall over Kerala — were fulfilled.
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“There has been widespread rainfall activity over Kerala during the past 24 hours and out of the 14 rainfall monitoring stations for declaring onset of monsoon over Kerala, 10 have received rainfall of 2.5mm or more. Thus, all the conditions for onset of monsoon over Kerala have been satisfied today, the 29th May 2022,” said a statement from the IMD.
In the days ahead, the southwest monsoon is expected to advance to “...remaining parts of Kerala, some more parts of Tamil Nadu, some parts of Karnataka, and some more parts of south and Central Bay of Bengal, some parts of northeast Bay of Bengal and northeastern States during next 3-4 days,” the statement added.
Last year too, the monsoon had been forecast to arrive by May 31 but officially landed on June 3 after which the progress was slow. The IMD used a specialised weather model to forecast the monsoon onset over Kerala and the forecast date had a built-in four-day margin of error.
Except for 2015, the monsoon had arrived within the four-day window of the date forecast by the IMD from 2005-to 2021, the IMD said in a press statement.
The IMD has forecast the June-September monsoon to be normal with rainfall likely to be 99% of the historical normal.