The onset of the monsoon over Kerala is likely be delayed by more than ten days from the normal date of June 1, Joseph P V, former director of India Meteorological Department (IMD), said. Joseph cites historical data
The onset of the monsoon over Kerala is likely be delayed by more than ten days from the normal date of June 1, Joseph P V, former director of India Meteorological Department (IMD), said. Joseph cites historical data and the occurrence of a band of raining clouds in the Bay of Bengal during the second week of May for the late onset.
Monsoon rains are critical for Indian agriculture with the majority of farms lacking irrigation facilities. The meteorological department has forecast an above-average monsoon for the year after El Nino adversely impacted the monsoon rainfall in 2015.
Joseph, now professor emeritus in the atmospheric science department at Cochin University of Science and Technology, says that historically, years succeeding an El Nino had a delayed monsoon.
“Another observation is that when a band of raining clouds called the Inter Tropical Convergence Zone (ITCZ) had anomalously high rainfall at its location close to and south of the equator in Indian and the West Pacific oceans during January to March, it crosses the equator to the northern hemisphere late, causing a delayed onset in India,” he says.
“The portion of raining clouds moving across to the Bay of Bengal named pre-monsoon rain peak (PMRP) has high and statistically significant correlation with the date of monsoon. If PMRP occurs in the first week of April, the monsoon occurs two weeks early. If PMRP occurs in the second week of May, onset gets delayed by about two weeks. In 2016, PMRP occurred during the second week of May,” Joseph said.
“This year, the band of clouds also generated a cyclone in the Bay of Bengal. After the cyclone died the raining area moved to the West Pacific Ocean, where it is located now. We are likely to get a dry spell over the northern Indian Ocean and peninsular India during the next ten days,” he said.
During the last 100 years, the average date of monsoon onset was June 1 with a standard deviation of eight days. After the onset over Kerala, monsoon rains spread northwards towards the Himalayas and westwards towards Rajasthan, covering the whole of India by mid-July. The march northwards and westwards is not at a uniform speed. There are halts, slow movement and spells of fast advance, Joseph said.