The much awaited southwest monsoon arrived over Kerala on Tuesday, but as a weak current that could take the system northwards along the west coast, but not eastwards into the peninsular region.

D. Shivananda Pai, Director of the Pune-based National Climate Centre and lead forecaster for monsoon, told The Hindu that the system could gradually move northwards and reach up to even Mumbai by the week-end, but the movement would be mainly confined to a narrow belt of about 100 km width along the west coast.

Rainfall, he said, was also likely to be only light and not heavy downpours that are typical of monsoon rains.

Things could improve

Mr. Pai, however, added that this was only the beginning of the monsoon. “This is only the first pulse of the system. One cannot jump to any conclusion. One has to wait and watch in the coming days. Things could improve down the line.”

He recalled that in 1983, the monsoon set in over Kerala only on June 12. But, the four-month season ended with excess rain — 113 per cent of the long period average that year.

Long-range forecast

In its long-range forecast for the season as a whole and the country in its entirety issued on April 26, the India Meteorological Department (IMD) announced that the monsoon this year was “mostly likely” to be normal, with a rainfall of 99 per cent of the long-period average (LPA), with a model error of plus or minus 5 per cent.

The forecast had noted that there was a 47 per cent probability of the rainfall to be between 96 per cent and 104 per cent, 24 per cent probability for it to be between 90 and 96 per cent, 17 per cent probability for it to be between 104 and 110 per cent, 8 per cent probability for being below 90 per cent and 4 per cent probability for being above 110 per cent of the LPA.

Earlier, a conference of national and international weather experts, organised by the IMD under the aegis of the World Meteorological Organisation in Pune on April 19 and 20, which looked at the likely monsoon scenario for the south Asia region as a whole, had predicted that the rainfall during the season was most likely to be within the normal range, but that there was a “slight tendency” for it to be below normal.

A statement issued at the end of the meet noted that there was likelihood of below normal rainfall over some areas of north-western and southern parts of South Asia, while being close to the long-period average over the remaining parts.

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