Southwest Monsoon season
The period June to September is referred to as the 'Southwest Monsoon' period. Southwest Monsoon period is the principal rainy season for the Indian subcontinent. This is the summer monsoon period where the southwest monsoon holds away over the country. The whole country receives nearly 75% of its rainfall during this period.
Southwest monsoon sets in over the extreme southwestern tip of the peninsula by the end of May. The onset of Monsoon is characterized by a sudden spurt of rainfall activity. It progresses inland in stages and covers the entire country by the middle of July.
It starts retrieving from the extreme northwest by the beginning of September, progressively receding southwards. Tamil Nadu is considered as a rain shadow region as it lies on the eastern (leaward side) side of western ghats. The total annual rainfall is maximum over the southernmost part of the state.