Normal or sub-par rains? IMD, Skymet have different takes

Over the past week, the country has seen two predictions about how monsoon is going to pan out. While one expected monsoon to slow down, the other forecast a better picture.

Two leading weather forecasting agencies — state-run India Meteorological Department (IMD) and privately-held Skymet — have come up with different views on the behaviour of southwest monsoon in the rest of the season.

While Skymet said monsoon in August and September would be ‘below normal’ due to a prolonged dry spell, the IMD said rainfall will be normal during the period. For August and September, IMD said the definition of normal is different and it is counted from 94106 of the long period average (LPA), while Skymet meteorologists questioned the change.

“If you see the standard deviation or error margin of June-September forecast that the IMD makes in April, it is +/- five per cent, while the forecast for August and September, the margin is +/- 8 per cent. Clearly, the normals are different and so are the error margins,” IMD DG KJ Ramesh said, adding that the IMD has been following the same practice for years.

For August, Skymet predicted that the southwest monsoon would be deficient at 88 per cent of the LPA with 70 per cent probability of rains being ‘ deficient’, while for September, it predicted that monsoon would be below normal at 93 per cent of the LPA.

“The cumulative monsoon deficit for the entire season is about 9 per cent. With 50-55 days to go for the season to end how will this cover up, when a big dry spell is expected,” Jatin Singh, CEO of Skymet said.

He said in some quarters, authorities should start preparing for drought, else they could be caught on the wrong foot.

The IMD, on the other hand, said that rains in August would not only be normal but could even be better than its forecast in June and could be about 96 per cent of the LPA. The IMD does not make predictions for September.

Skymet lowered its full season monsoon forecast to ‘below normal’ from ‘normal’ because of poor monsoon in August and September, coupled with insufficient rains in June and July, but the IMD is sticking to its earlier forecast that rains in June to September of 2018 would be ‘normal’ at 97 per cent of the LPA with a model error of +/-5 per cent.

“End of July, the El Nino is at 0.3, which isn’t harmful, while the Indian Ocean Dipole is positive. The Oceanic Nano Index (ONI) is also negative so far. All these are making us confident that monsoon over the next two months will be normal, and its distribution will be good, which would aid kharif crops,” Ramesh said.

He said in June and July, monsoon has been fairly distributed or else the difference between area sown last year compared to this year wouldn’t have come down from 8 per cent to less than 2 per cent in a span of few weeks.

Skymet, however, said that the sea surface warming is continuing in the Pacific Ocean and is indicating towards an evolving El Nino.

It is not the first time that the IMD and Skymet have differed over their forecasts. In 2017, Skymet in its forecast had expected August rains to be 7 per cent below normal, while in September it said that rains would be 4 per cent below normal. The IMD in its updated forecast said that August rains would be just 1 per cent below normal while in September too the monsoon would be normal. The forecast was with a model error of +/-9 per cent. In reality, August rains were 13 per cent below normal, while September saw a 12 per cent shortfall.