IMD's faulty forecast for N India: Wrong signals by models, difficulty in predicting wind patterns
Wrong signals by models, difficulty in predicting the outcomes of the interactions between the easterly and westerly winds were some of the major reasons behind the India Meteorological Department's monsoon forecast for parts of north India going haywire, experts pointed out as any relief from the oppressive heat eludes the region.
The Southwest Monsoon has reached almost all parts of the country but has stayed away from parts of north India. It is yet to reach Delhi, Haryana, parts of west Uttar Pradesh and west Rajasthan. The India Meteorological Department (IMD) had predicted that monsoon is expected to cover these parts by June -- a little less than a month back, but its predictions are yet to come true.
In its forecast on June 13, the IMD had predicted that the Southwest Monsoon will reach Delhi by June 15. However, a day later it said conditions are not favourable for its further advancement in this region.
Then began a long 'break-spell' during which the Southwest Monsoon was weak over several parts of the country.On July 1, the IMD said conditions could be favourable for further advancement of the monsoon by July 7. The moist easterly winds in the lower level from the Bay of Bengal are likely to establish gradually over parts of eastern India from July 8, it had said.
On July 5, the IMD again said the monsoon is likely to spread into northwest India covering Punjab and north Haryana by July 10. However, there were no signs of any relief even on July 10.
On forecasting the onset of Southwest Monsoon over Kerala, the IMD said it would hit the southern state by May 31. Till May 30, the IMD, in its daily bulletin, said the onset of the monsoon over Kerala was expected to be around May 31. However, by an afternoon of that day, it revised it saying the onset is expected to be by June 3.
“We could have told (the delayed onset) in the morning itself. However, we are monitoring all the defined parameters/ criteria for the onset of monsoon over Kerala. At present the criteria are not fully satisfied,” IMD Director General Mrutunjay Mohapatra had said on May 30.
Mohapatra said the country's forecasting agency did issue a forecast that monsoon will cover parts of north India including Delhi by June 15 as indicated by the models. “But we changed it the next day (June 14) when we realised that conditions are not favourable for its advancement.”
He said the forecast models did not show consistency in the interactions of the easterlies and the westerlies -- the two dominant wind patterns.
Mohapatra added that the accuracy of the models is reasonably good when it comes to forecasts up to two weeks but not as good for forecasts for four weeks.
M Rajeevan, Secretary, Ministry of Earth Sciences, who has spent over 35 years studying the Southwest Monsoon, said the forecast models gave wrong signals.
“The models have picked up very well some of the broader events like a break in the monsoon and its revival a week ago. But when it comes to local forecasts like its advancement over Kerala or rain over parts of north, there is an issue,” Rajeevan said.
“With regards to the forecast of advancement of monsoon over parts of north India, including Delhi, it was too early. The IMD should not have issued the forecast. They could have waited for some more time,” he said. The IMD is an institute under the Ministry of Earth Sciences.
Tracking the interactions of the westerlies and the easterlies is the most difficult part in monsoon forecast, Mohapatra's predecessor K J Ramesh said.
In a normal scenario, the Southwest Monsoon covers West Bengal and many parts of central India by June 15, just 14 days after it makes an onset over Kerala, making the official commencement of the four-month rainfall season over the country. It, however, takes nearly three weeks to cover parts of north India, Ramesh said.
This is also because of the interactions of easterlies and westerlies. Between the westerlies and the easterlies, the former is a “big brother”, he said. The easterlies only gain strength when there is a low pressure area that can help it advance further. This usually creates a “sea-saw” like situation. This is also one of the reasons when north India sees a break in the monsoon, he explained.
“They (the IMD) must have seen some strength of monsoon capable of moving westwards (towards) north India which is why they issued the forecast (of monsoon covering the remaining parts of north India, including Delhi). The anticipation of the see-saw effect, the judgement, did not come true,” Ramesh said.
Ajit Tyagi, former IMD Director General, said the forecasting agency had predicted that in the first surge the Southwest Monsoon could cover the country by June 15-16.
But then it weakened and there were clear signs that it would not revive before July 10. That was indicated. If one looks at the Medium Range Forecast of 10-15 days, it was right, Taygi said.
“Initial forecasts were not realised but the IMD did make course corrections,” he added.
