The northeast monsoon this time was not expected to cause bountiful rainfall. But, till Monday, the State received 50 per cent higher rainfall than the normal amount.

Against the normal 375 mm, the State, since October 1, recorded 562 mm, a departure of 50 per cent. Puducherry registered 22 per cent excess rainfall.

Explaining the surprise element of the monsoon, Y.E.A. Raj, Deputy Director General of Meteorology, says that several factors such as the continued positive value of southern oscillation, Siberian High and tropical jet stream were taken into account while making the earlier assessment.

Since 2004, the rainfall departure from the anticipated amount, as recorded by the State during the northeast monsoon, was either excess or on the positive side of normal value.

Law of averages

The excess rainfall was experienced in 2005, 2007 and 2008. This was why it was expected that the law of averages would apply this time.

Actually, in consonance with the forecast of meteorologists, the delayed onset of monsoon and the relatively dry October took place.

While attributing the present rain spell to the impact of easterlies, Dr. Raj says the actual causes for the bountiful rainfall have to be researched and analysed further. As regards the season's rainfall [October 1 - December 1], most of the districts recorded excess rainfall. Among them were Tiruvarur – 75 cm (deviation from normal: 57 per cent); Kanyakumari – 73 cm (99 per cent); Dindigul – 66 cm (103 per cent); Ariyalur – 65 cm (64 per cent); Thanjavur – 64 cm (56 per cent); Madurai – 62 cm (93 per cent) and Ramanathapuram 61 cm (61 per cent). Nagapattinam recorded eight per cent normal rainfall with 70 cm. Chennai and Tiruvallur fell in the category of deficient districts with 39 cm (minus 35 per cent) and 37 cm (minus 24 per cent).

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