May 14, 2011 12:35:06 am
According to Met officers,the onset of south west monsoon over Kerala this year will be on May 31,the usual onset date being June 1.
The Met officers had earlier told The Indian Express that this year the onset date would be the normal date with a plus or minus four as error. The onset date over Kerala was not to change even as onset dates for other states are likely to change according to our assessment, said Ajit Tyagi,director general of India Meteorological Department (IMD),here on Friday.
The conditions were favourable for a normal onset in the country for this year and the Met department will be closely observing the progress of the monsoon from Kerala,Tyagi told the The Indian Express after the official announcement.
A panel of 40 weather scientists are working on revising the normal onset dates,as they were based on monsoon data between the years 1932-70. The present scenario is that the Met department has more comprehensive analysis of the seasonal rains till 2009. Last year,the forecast onset date given was May 30 and the actual onset happened a day later on May 31.
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Tyagi said the operational forecasts given by the IMD in last six years have been correct. The onset date is assessed on the advance of monsoon over the Andaman Sea around May 20. As of now the monsoon flow is likely to appear over Andaman sea within next few days and is likely to cover Andaman sea close to its normal date, said Tyagi.
The Met department has stated that past data suggests absence of any one association between the date of monsoon advance over the Andaman Sea and the date of monsoon onset over Kerala. The Met department has attributed the predictions for the 2011 monsoon onset to the model based on principal component regression techniques which uses six predictors minimum temperature over north-west India; pre-monsoon rainfall peak over south peninsula; outgoing long wave radiation over south China sea; lower tropospheric zonal wind over southeast Indian ocean; upper tropospheric zonal wind over the east equatorial Indian Ocean; and outgoing long wave radiation over south-west Pacific region.
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