What causes rainfall on the coastal areas of Tamil Nadu in the beginning of winters ?

The correct answer is North-Eastern monsoon.

Key Points 

Northeast monsoon:

• Retreating monsoon in India can be experienced in October-November.
• Monsoon winds are retreating gradually and the sudden rise of temperature with October heat.
• Day temperature is high and nights are cool and pleasant. 
• The average minimum temperature falls below 20o C.
• It leads to rainfall over Tamil Nadu, Kerala, Andhra Pradesh, Karnataka and Telangana.
•  Its direction is from northeast to southwest.
• A minor part of the annual rainfall in India is due to this type of North-Eastern monsoon.

​Thus, the northeastern monsoon causes rainfall on the coastal areas of Tamil Nadu at the beginning of winters.

Additional Information 

Monsoon:

• The term ‘monsoon is derived from the Arabic word 'mausim', meaning season.
• ​A monsoon is a seasonal change in the direction of the prevailing, or strongest, winds of a region.
• Monsoons cause wet and dry seasons throughout much of the tropics.
• Monsoons are most often associated with the Indian Ocean and the Indian sub-continent. 

Southwest monsoon:

• Southwest monsoon in India can be experienced in June-September.
• The whole of India comes under the southwest monsoon.
• India faces severe cyclones and thunderstorms.
• The temperature remains low during July and August.
• This rises high in September with a decreasing amount of precipitation.
• A major part of annual rainfall in India is due to the South-West monsoon.