Monsoon in India and Tamil Nadu
From early June to mid-September is the duration of the monsoon. Most parts of the country get rainfall in this period. South India typically gets rainfall from southwest monsoons due to extreme South-West trade winds blowing to the northern hemisphere.
During the summer, as the land gets heated up, central India turns into a low-pressure region while the waters of the Arabian Sea turn into a high-pressure region. Winds blew from the high-pressure region to the low-pressure region. So, these winds move from the Arabian Sea to land, thus carrying moisture in the form of monsoon clouds called the South-West monsoon. However, these monsoons emerging from the Arabian Sea get hindered by the Western Ghats. These western ghats which expand from South Gujarat to South Tamilnadu block the clouds resulting in the clouds losing their moisture. This turns rainfall in the Western Ghats. Tamilnadu being in the rain shadow area of Western Ghats does not receive rainfall from these monsoons.
Why does Tamil Nadu coast achieve winter rainfall?
The geographical location of Tamil Nadu, the east coast receives rainfall as the northeast trade winds blow from the sea to land in this location, and because of this Tamil Nadu receives winter rainfall.