Thiruvananthapuram: The southwest monsoon has made an onset over Kerala, marking the commencement of the four-month long rainfall season, the India Meteorological Department confirmed on Monday.
"The southwest monsoon has made an onset over Kerala," IMD director general Mrutyunjay Mohapatra said.
This is the second time this decade when the southwest monsoon has arrived on the dot, on June 1. Last time it came on the traditionally appointed date was 2013.
Yellow alert has been declared in nine districts of Kerala including Thiruvananthapuram, Kollam, Pathanamthitta, Alappuzha, Kottayam, Ernakulam, Idukki, Malappuram and Kannur.
The four-month monsoon season from June to September accounts for 75 per cent of rainfall in the country.
Accurate forecast
And once again, the Indian Meteorological Department's prediction was more or less on target. The IMD had predicted the 2020 onset on June 5 but it has come four days earlier on June 1. But the actual onset date fell within the accepted model error of plus or minus four days.
The only time the prediction fell outside the model's accepted target circle since 2005, the year the statistical prediction technique was indigenously developed, was in 2015. Then, the IMD forecast the southwest monsoon to make a landing on May 30 but the rains actually ended up coming only on June 5, five days later.
In 2017 and 2018, the IMD prediction was bang on. In 2017, the IMD said the rains would come on May 30, and it came on that day. In 2018, the IMD said the monsoon will lash Kerala on May 29, and May 29 it was.
Most other years, the difference between the IMD date and the onset were two to three days. In 2013, the only other year in the last 15 years when the monsoon arrived on June 1, the IMD had said it would arrive on June 3.
The model based on Principal Component Regression technique uses the following six predictors: i) Minimum Temperature over North-west India, ii) Pre-monsoon rainfall peak over south Peninsula, iii) Outgoing Long wave Radiation (OLR) over south China Sea, (iv) Lower tropospheric zonal wind over southeast Indian ocean, (v) upper tropospheric zonal wind over the east equatorial Indian Ocean, and (vi) Outgoing Long wave Radiation (OLR) over south-west Pacific region.
Skymet Weather, a private weather forecasting agency, had on May 15 said the southwest monsoon will touch down at Kerala on May 28 with an error bracket of plus or minus two days.
Conditions have favourable for the onset of the monsoon over Kerala due to the formation of Cyclone 'Nisarga' over Arabian Sea.
On April 15, Madhavan Rajeevan, Secretary of Ministry of Earth Sciences forecast that monsoon rains this year are likely to be normal at 100 per cent of the long period average with a model error of 5 per cent.
Skymet on May 30 had declared arrival of monsoon, but the IMD had differed, saying conditions were not ripe then for such an announcement.
