P. Sunderarajan

Last year, the onset was forecast for May 26 but it arrived on May 23

NEW DELHI: The Indian Meteorological Department (IMD) has announced that the Southwest Monsoon is likely to set in over Kerala on May 30. The forecast is subject to a model error of plus or minus four days.

In a press release, the IMD also said the monsoon flow was expected to appear over the Andaman Sea by next week and cover the entire sea by May 20, close to the normal date for the region.

Last year, the IMD forecast a May 26 onset but the monsoon arrived on May 23.

In 2008 the forecast was for May 29 and the actual date was May 31, in 2007 the respective dates were May 24 and May 28, in 2006 May 30 and May 26 and in 2005 June 10 and June 7.

Meanwhile, the IMD last month forecast a normal rainfall for this year with a precipitation of 98 per cent of the Long Period Average, subject to a model error of plus or minus five per cent for the entire season (from June to September) and for the country as a whole.

Last year, the agency forecast a rainfall of 94 per cent plus or minus five per cent in April and then fine tuned it to 93 per cent plus or minus four per cent. But, the country received a rainfall of 78 per cent of the LPA only for the season.

IMD experts said a normal onset need not necessarily mean that the rainfall would be normal for the season as a whole as the country was too huge and the season spread over a long period of four months. It took two months to even cover the entire country.

Last year, the onset took place on May 23, eight days before the normal date, but the season ended with a whopping deficiency of 22 per cent.

IMD announced the forecast for the onset at the end of a media workshop organised by the agency. The workshop focussed on the complexities of weather forecasts and the uncertainties inherent in long range forecasts in the tropical region. Experts like Sulochana Gadgil of the Indian Institute of Science and M. Rajeevan of the Indian Space Research Organisation, emphasised that the weather system was far more chaotic over the tropical region compared to the extra-tropical one.