Due to the peculiar shape of the Indian peninsula, the south west monsoon winds bifurcate into two branches – Arabian Sea branch and Bay of Bengal branch before entering the land.
Arabian Sea branch :
The Arabian Sea branch that reaches Kerala coast by the beginning of June gives heavy rainfall there. Then it advances to the states of Karnataka, Goa, Maharashtra and Gujarat and causes rainfall in the western parts.
Bay of Bengal branch :
The Bay of Bengal branch which absorbs moisture from Bay of Bengal advances through Sundarban delta and enters West Bengal and bifurcates into two. One branch enters the Brahmaputra plains and gives heavy rainfall in the north eastern states. Khasi, Garo hills obstruct the winds to cause rainfall.
The other branch enters the Ganga plains and gives rainfall in the states of West Bengal, Bihar and Utter Pradesh. This branch joins with the Arabian Sea branch in the Punjab plain, moves northward and gives heavy rainfall in the foothills of the Himalayas.
