Southern Oscillations (ENSO), Indian Ocean Dipole also have a role in helping or disrupting the South-West Monsoon.
Findlater Jetstream from the coast of Somalia towards Indian Peninsula strengthen the Monsoon winds.
2 BRANCHES OF THE ADVANCING MONSOON
The South-West Monsoon on reaching the coast of the Indian Monsoon is divided into 2 branches:
Arabian Sea Branch
Bay of Bengal Branch
Arabian Sea Branch: This branch hits the Western Ghats which acts as a barrier preventing the monsoon to reach the other side of the mountains. Thus, resulting in drought-like situations in various parts of Karnataka, Maharashtra & Telangana. The Monsoon winds are shifted northwards and mostly enter the Indian Peninsula through the Kathiawar Peninsula in Gujarat.
Bay of Bengal Branch: The Bay of Bengal Branch is responsible in causing heavy rainfall in Sri Lanka, Andaman & Nicobar Islands, North-East India, & East India. These monsoon winds are deflected by the mountains in North-East India such as the Patkai Bum, Purvanchal etc and are forced to reach Central as well as North India. That is the reason why North India gets less rainfall as compared to North-East India as the intensity of the Monsoon weakens by that time.
REASONS FOR RETREATING MONSOON
High Pressure at North India
Westerly JetStream start flowing South of the Himalayas in winters (In summers they flow north of the himalayas towards Tibet)
Shifting back of ITCZ to it’s original position
While retreating, the North-East Monsoons cause catastrophic floods in Tamil Nadu (Chennai floods) as they pick moisture from the Bay of Bengal Coast of India. That is why Tamil Nadu mostly gets rainfall in winters.