Statistics relating to the date of onset of the southwest monsoon over Kerala for the 100-year period 1891-1990 reveal that the mean and median dates of onset for south Kerala are 31 May and 1 June, with a standard deviation of 8.5 days. Declaring the date of monsoon onset is not a straightforward matter. However, rainfall pattern, uppper air circulation features and INSAT cloud pictures are useful guides, and these indicate that the onset date in 1990 esd 17-18 May. During 1891-1990 there have been onlyy 12 years in which the date of onset over Kerala has been on or before 18 May.

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