The much awaited northeast monsoon, which accounts for about 43 cm of Tamil Nadu's annual rainfall of around 92 cm, has set in over the State.

Normally expected to last till December-end, the monsoon is beneficial to Tamil Nadu, Kerala and parts of Andhra Pradesh such as Rayalaseema and coastal areas in south Andhra Pradesh. Some areas in coastal Tamil Nadu receive more than 100 cm. The monsoon also extends to parts of Sri Lanka, especially over the eastern coast.

Rainfall during the NE monsoon is of immense societal significance to the human population of 15 crore as it supports the main cultivation season, known as Rabi or Samba, in south India and Maha in Sri Lanka.

“Normally, the monsoon, which brings in 85 cm of rainfall to the city, sets in around October 20. c,” Y.E. A. Raj, Deputy Director-General of Meteorology, Regional Meteorological Centre, Chennai, said.

In 2009 and 2010, the advent of the monsoon was announced on October 29.

The presence of a weak trough off the east coast of Tamil Nadu and a weak low pressure off Kerala coast led to the onset of the monsoon over Tamil Nadu and Puducherry.

The Meteorological department declared that the southwest monsoon had withdrawn from entire Bay and the entire Arabian Sea.

During the 24-hour period ending 8.30 a.m. on Monday, many areas in the State received heavy rainfall, including Sankarankoil (Tirunelveli district) 10 cm and Red Hills (Tiruvallur) 9 cm.

As for the longevity of the present rain spell, Dr. Raj said his department's dynamic models indicated that it would go on for a week (October 31).

On the forecast for the monsoon this time, he said that it was expected to be normal. However, he hastened to add that the monsoon was known to be unpredictable. Besides, long dry spells were a feature of the monsoon.