Monsoon explained: After its onset over Kerala, the monsoon spreads over the entire country by July 15.
The IMD announced the onset of Southwest Monsoon over Kerala on Thursday, marking the commencement of the four-month rainy season in the country. The normal date for the onset of the monsoon over the Kerala coast was June 1. After its onset over Kerala, the monsoon spreads over the entire country by July 15.
The IMD’s weather summary had stated, “The south-westerly winds could strengthen further gradually from June 1, resulting in enhancement of rainfall activity over Kerala. The monsoon onset over Kerala is likely to take place on June 3.”
IMD had forecast the onset of the monsoon over the Indian mainland for May 31. On May 21, the southwest monsoon arrived over the Andaman Sea, however it did not progress further. On May 26 Cyclone Yaas made landfall on the coasts of northern Odisha and West Bengal.
What does the ‘onset of monsoon’ mean?
The onset is a big day for the Indian economy every year – the first rain over Kerala will mark the beginning of the four-month, June-September southwest monsoon season across India. This will bring more than 70 per cent of the country’s annual rainfall.
Meteorologists check for the consistency of rainfall over a defined geography, its intensity, and wind speed and then declare the arrival of monsoon.
To be precise, the onset of the monsoon is declared after at least 60 per cent of the 14 designated meteorological stations in Kerala and Lakshadweep record at least 2.5 mm of rain for two consecutive days at any time after May 10. That’s not all, wind and temperature are also a major factor in declaring the onset of monsoon.
Is there anything to worry because of the delay?
No, there is nothing to worry about. Last year, the monsoon was exactly on time. It had hit the Kerala coast on June 1, 2020, in 2019, the IMD had announced a delay of six days — and predicted the onset for June 6. The monsoon finally set in on June 8, 2019.
In 2017 and 2018, the monsoon came early and hit the Kerala coast on May 30 and May 28 respectively.
Is it a sign of poor monsoon?
No. The onset is just an event that happens during the progress of monsoon over the Indian subcontinent.
The time of the onset — a delay of a few days, or perhaps the monsoon arriving a few days early — has no bearing on the quality or amount of rainfall during the four-month monsoon season.
According to IMD, India manages to receive about 116 cm of rain every year and 89 cm of it comes in the southwest monsoon season. The date of the onset of the monsoon does not impact the overall rain that India gets during a particular southwest monsoon season.
However, a delayed onset can impact the arrival of monsoon in other parts of the country, especially in the southern states, which start getting rain within days of the monsoon reaching the Kerala coast.