The normal date of the onset of the southwest monsoon over Kerala, the southern tip of India, is 1 June. The monsoon takes about a month and a half to travel from Kerala to west Rajasthan and it does not advance into the country at a constant speed. See map below:

1.4.1 Onset Dates

If you want to know how the southwest monsoon has been progressing this year over India, the best way is to visit the official web site of the India Meteorological Department (IMD) at www.imd.gov.in.

As per IMD, the southwest monsoon arrived over Kerala on 31 May 2010.

IMD’s long range forecast for the 2010 southwest monsoon season (June to September), issued on 23 April 2010, is that the rainfall for the country as a whole is likely to be Normal. Quantitatively, monsoon season rainfall is likely to be 98% of the long period average with a model error of ± 5%. The long period average rainfall over the country as a whole for the period 1941-1990 is 89 cm. To read the full text of the long range forecast, visit the IMD web site.

On 25 June 2010, IMD issued an update on the above forecast and also additional forecasts for homogeneous regions and for the months of July and August. They are available on the IMD web site.

Another good site is Monsoon On Line hosted by the Indian Institute of Tropical Meteorology, Pune, on which you can see daily, weekly and seasonal rainfall statistics of the southwest monsoon rainfall over India and the current satellite imagery.

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