How the monsoon develops every year and visits India

Every year, around the first week of June, a vast expanse of roiling grey clouds advances from the Arabian sea and makes landfall in Kerala to the tune of rumbling booms of thunder. Sheeting rain soon encompasses the whole state as the southwest monsoon sweeps over it.

From June to September, the southwest or summer monsoon moves across India, bathing the country in rain—during this period, India receives 70-90% of its annual rainfall. In the cooler months, from October to November, the retreating monsoon or the Northeast monsoon sets in, and brings rain to the eastern coast of India, especially Tamil Nadu. 

What causes the southwest or summer monsoon?

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