CHENNAI: The northeast monsoon, which caused unprecedented floods in Tamil Nadu from late October to early December, has withdrawn.

The Meteorological department, in a bulletin on Wednesday, made the announcement. But some experts feel that the principle of monsoon withdrawal on real-time basis should not be made applicable to the northeast monsoon, given its unique characteristics.

Cessation of rainfall

In the case of northeast monsoon, easterlies last till March or April. So, the cessation of rainfall all over the State is taken as the basis for the withdrawal. This time, southern coastal parts of the State recorded rainfall even in the first half of January. Till January 18, Pamban received 12 cm followed by Kanyakumari (11 cm) and Tuticorin (4 cm).

In the case of the southwest monsoon, change in wind circulation features is considered an important parameter for withdrawal. This is why the system of announcing the withdrawal on real-time basis is more relevant for southwest monsoon, the experts argue.

Giving an instance, Mumbai does not experience torrential rain in September as it does in July. However, the department's official line is that when the onset of the northeast monsoon is announced, details regarding the withdrawal too should be publicised. It is not uncommon for the northeast monsoon to spill over to January. Since 1901, it withdrew in January on 30 occasions.

As for the official definition of seasons, the period October to December is considered northeast monsoon, irrespective of the date of onset or withdrawal. Going by this yardstick, the State recorded 77 cm, a deviation of 79 per cent. All the districts except Tuticorin recorded excess rainfall.

The monsoon of 2005 saw the formation of five cyclonic systems over the Bay of Bengal whereas the average number is 3.60, going by an official study on northeast monsoons from 1971 to 2004.

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