A fisherman at work ahead of southwest monsoon in Kochi, Kerala, on Saturday, May 29. (PTI)
A fisherman at work ahead of southwest monsoon in Kochi, Kerala, on Saturday, May 29. (PTI)

Will never manipulate data to justify forecasts: IMD on monsoon forecast lapse

Monsoon is likely to make onset over Kerala around June 3, two days after its normal onset date of June 1, IMD said on Sunday after predicting May 31 as the date for the onset
By Jayashree Nandi
UPDATED ON MAY 31, 2021 09:54 AM IST

Monsoon is likely to make onset over Kerala around June 3, two days after its normal onset date of June 1, India Meteorological Department (IMD) said on Sunday.

On May 28, the department had said that monsoon was likely to make onset over Kerala on May 31, a day ahead of its normal date. Its May 14 forecast had also predicted the arrival of monsoon over Kerala on May 31, with a possible error margin of plus/minus four days.

After very severe cyclone Yaas weakened, scientists said it had helped strengthen monsoon winds. Very heavy to heavy rain was reported in different parts of Kerala on May 27 and 28.

But rains stopped and no heavy rain has been recorded over Kerala since then. “It should rain for two consecutive days in a certain number of stations. That has not happened. The westerlies should have a certain depth and it should be very cloudy. All these factors have to be met for us to announce onset [of monsoon]. These conditions may start from June 1 and meet the criteria by June 3,” said M Mohapatra, director general, IMD.

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Addressing the lapse in the forecast, M Rajeevan, secretary, ministry of earth sciences, tweeted,“@Indiametdept will never manipulate data or make statements to justify their forecasts. They admit forecast failures with humility. In weather & monsoon forecasts, no one can be perfect. We are also accountable to Indian tax payers. We show respect to our country.”

According to IMD’s monsoon onset parameters, after May 10, 60% of the available 14 stations enlisted-- Minicoy, Amini, Thiruvananthapuram, Punalur, Kollam, Allapuzha, Kottayam, Kochi, Thrissur, Kozhikode, Thalassery, Kannur, Kudulu and Mangalore should report rainfall of 2.5 mm or more for two consecutive days, depth of westerlies should be maintained up to 600 hPa, outgoing longwave radiation (OLR) value should be below 200 wm-2 ( watt per sq metre). OLR represents the total radiation going to space emitted by the atmosphere or the extent of cloudiness.

Southwest monsoon normally sets in over Kerala around June 1. It advances northwards, usually in surges, and covers the entire country around July 5.

Skymet Weather, a private weather forecasting company, however, announced onset of monsoon on Sunday--May 30, two days ahead of normal monsoon onset date of June 1. “A set of environmental conditions need to be fulfilled as a criterion for the arrival of monsoon. By and large, all parameters have satisfied the required threshold, essentially the rainfall and depth and speed of westerly winds over the southeast Arabian Sea and adjoining equatorial Indian Ocean. Rainfall amounts are verified from the available data on the official website,” Skymet Weather said in a statement.

“Often the copybook criteria of monsoon onset is not met. As on today, the westerly wind profile parameter has been met and 60% of the 14 stations have recorded over 2.5 mm rain for consecutive days. OLR is low so that criteria is not met,” explained Mahesh Palawat, vice president, climate change and meteorology, Skymet Weather.

“At present, the criteria are not fully satisfied. For example, the rainfall over Kerala has decreased today along with weakening of westerly winds. Also, the depth of westerly winds did not increase up to 4.5 km against the expectation. The convective cloud development leading to enhancement of rainfall activity over Kerala in such a scenario is not expected at least up to June 1,” IMD’s Mohapatra added.

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