Skymet may revise monsoon forecast again; June-July predictions off the mark
Skymet may revise its monsoon forecast after its July prediction turned out to be off the mark and rainfall in June was higher than estimated.
Rainfall last month, which the private agency had said would be 4 per cent above normal, was 17 per cent below average, while June rainfall was 16 per cent above average compared with a 7 per cent surplus forecast by Skymet. The state-run India Meteorological Department had predicted an 8 per cent deficit in July and had not put out a forecast for June. The weather office expects this year’s monsoon to be 88 per cent of the long-period average.
While Singh conceded that Skymet had got the July forecast wrong, he said the gap in June was “acceptable.” “The acceptable deviation of a monthly forecast is plus-minus 9 per cent. So, June was right, but yes, we went wrong on July,” he said.
“Between the long- and medium-range forecast, in the summer it is relatively easier to get the season and 15-day weather forecast right. The challenge is giving monsoon forecast for 15 days and up to three months. That is when the swing happened,” said Singh.
He added that the Madden Julian Oscillation, which brings rainfall over the subcontinent, was favourable until June 28, after which it entered a 50-day cycle and turned unfavourable.
“The monsoon forecast is like a four month-long marathon, so some phases may be great and some weak, but for the season we think it will be normal,” he said. As of Sunday, monsoon rainfall across the country was 6 per cent below normal, according to the IMD.
Skymet obtains data from various global forecasters in the US, Japan and Australia. “In July, we mis-calibrated the quantum of rainfall because of the excess that was in June. So we have now recalibrated our model and slightly downgraded August and upgraded September,” said Singh.
Rainfall in June, at about 163 mm on average, is the lowest during the fourmonth monsoon. A small deviation in June could make forecasts more vulnerable, said GP Sharma, VP-metetorology at Skymet.
“In the month of July, the El Nino remained all through and reached its peak during second and third week of the month, leading to less rainfall,” he said, referring to the phenomenon of warming waters in the Pacific Ocean that affects weather patterns around the world. Skymet provides weather information to governments, companies, commodity markets, international organisations and banks.