Difference between Advancing and Retreating Monsoon

India experiences two main monsoon phases. The Advancing Monsoon occurs from June to September and brings widespread rainfall across most parts of the country. The Retreating Monsoon occurs from October to December and mainly affects the southeastern coastal regions of India.

Together, these two phases provide the majority of India’s annual rainfall and make the monsoon system vital for the country’s agriculture and overall development.

Advancing Monsoon (Southwest Monsoon)

The Advancing Monsoon is the beginning of the rainy season in India. During this time, warm and moist winds blow from the southwest direction, mainly from the Indian Ocean and Arabian Sea, towards the land. These winds bring heavy rainfall to most parts of the country during the summer months.

Advancing Monsoon Mechanism and Origin

The Advancing Monsoon is caused by the differential heating of land and sea during summer. Intense heating of the Indian landmass creates a strong low-pressure area over northern India, while high pressure develops over the southern Indian Ocean (Mascarene High).

Air moves from high pressure to low pressure areas. As these winds cross the equator, they are deflected by the Coriolis force and become south-westerly winds, carrying moisture from the oceans towards India.

The northward shift of the ITCZ further strengthens this low-pressure zone and triggers the onset of monsoon rainfall over the Indian subcontinent.

The Southwest Monsoon generally reaches the Kerala coast around early June and gradually advances across the country. It progresses through two major branches:

• Arabian Sea Branch: Moves along the western coast, causing heavy orographic rainfall along the Western Ghats and then penetrating into central and northern India.
• Bay of Bengal Branch: Moves towards Northeast India, is deflected by the Himalayas, and spreads over the Indo-Gangetic plains.

By mid-July, the monsoon typically covers the entire Indian subcontinent.

Spatial Distribution of Advancing Monsoon 

Rainfall distribution during the Advancing Monsoon is highly uneven:

• Western Ghats and Northeast India receive extremely heavy rainfall
• Indo-Gangetic plains receive moderate rainfall
• Rajasthan and Gujarat receive low rainfall due to arid conditions
• Tamil Nadu remains relatively dry due to rain shadow effect

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Retreating Monsoon (Northeast Monsoon): Mechanism, Origin and Withdrawal

The Retreating Monsoon marks the withdrawal of the Southwest Monsoon from the Indian subcontinent and the beginning of the dry season. It generally occurs from October to December.

Mechanism and Origin

As the Sun shifts southward after September, the Indian landmass starts cooling. The low-pressure system over north and northwest India weakens and is replaced by high-pressure conditions. At the same time, the surrounding seas remain relatively warmer, creating a reversal in the pressure pattern.

Due to this change, winds reverse direction and begin to blow from land to sea as north-easterly winds. These winds are generally dry, but while passing over the Bay of Bengal, they pick up moisture and cause rainfall in parts of southeastern India, especially Tamil Nadu.

Withdrawal of Retreating Monsoon

The withdrawal of the Retreating Monsoon is a gradual process that begins in northwest India in September and progresses southwards. By December, the monsoon completely withdraws from the Indian subcontinent. This transition period is often associated with warm and humid conditions known as the “October Heat”, characterized by high temperature and humidity due to clear skies and residual moisture. Unlike the Advancing Monsoon, the Retreating Monsoon is highly region-specific:

• Tamil Nadu, Puducherry, and coastal Andhra Pradesh receive significant rainfall
• Tamil Nadu receives the majority of its annual rainfall during this phase
• This rainfall is crucial for samba rice cultivation
• The Bay of Bengal becomes highly active for cyclone formation

Differences Between Advancing and Retreating Monsoon in India

The Advancing and Retreating Monsoon are two contrasting phases of India’s monsoon system. While the Advancing Monsoon brings widespread rainfall essential for agriculture across most of India, the Retreating Monsoon is more localized but crucial for southeastern coastal regions and cyclone formation in the Bay of Bengal. Together, they shape India’s agricultural cycle and disaster patterns.