The Northeast Monsoon and its Effect
During winter, the weather conditions are influenced by high pressure developed over Northwestern part of the subcontinent.
This results in the blowing of cold dry winds from these regions towards southern low pressure areas lying over water bodies surrounding peninsular India.
Since these winds are cold and dry, they do not cause rainfall and weather conditions under their influence remain cold and dry.
However; wherever these Northeast monsoon winds collect moisture while passing over the Bay of Bengal, they bring rain along Coromandel Coast.
These winds are planetary winds known as Northeast Trades.
In India they are essentially land bearing winds.
The Southwest Monsoon and its Effect
During summer, the northwestern parts of India become very hot due to very high temperature.
This is ascribed to the apparent shift of the sun in northern hemisphere.
This results in the reversal of air pressure conditions not only in northwestern India but also on water bodies surrounding the peninsular.
As a result, Northeast Trade winds are replaced by Southwest monsoon winds.
Since these winds are sea bearing and blow over warm water bodies before reaching land, they are moisture laden, causing wide spread rain over the most parts of India.
This period of southwest monsoon from June to September, is known as the rainy season for most parts of the country.