The retreating monsoons occur during the months of

1. Indian Climate: The Four-Season Cycle (basic)

To understand the complex Indian Monsoon, we first need to look at the broader framework: the Annual Cycle of Seasons. In India, the climate isn't just a background setting; it is a rhythmic cycle that dictates agriculture, festivals, and daily life. While we often think of 'summer' and 'winter', meteorologists in India recognize a more nuanced four-part division to account for the unique behavior of the monsoon winds INDIA PHYSICAL ENVIRONMENT, Geography Class XI, Chapter 4, p.31.\n\nAccording to the India Meteorological Department (IMD), the year is divided into these four distinct seasons:\n

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• The Cold Weather Season (Winter): Generally from December to February, characterized by clear skies and low temperatures in the north.
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• The Hot Weather Season (Summer): From March to May, where temperatures soar as the 'heat belt' moves northward.
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• The Southwest Monsoon Season (Rainy): From June to September, the period of heavy rainfall and high humidity.
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• The Retreating Monsoon Season (Transition): During October and November, when the monsoon winds begin to withdraw from the mainland INDIA PHYSICAL ENVIRONMENT, Geography Class XI, Chapter 4, p.31.
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\n\nBeyond this scientific classification, India has a deep-rooted cultural tradition of dividing the year into six seasons or ṛitus, each lasting roughly two months. This system is still widely used in north and central India to track agricultural and festive calendars. However, it is important to note that this six-season cycle is less distinct in South India, where the proximity to the sea and the equator keeps temperatures more uniform throughout the year INDIA PHYSICAL ENVIRONMENT, Geography Class XI, Chapter 4, p.37.\n\n\n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n

Traditional Ritu	Approx. Months	English Equivalent
Vasanta	March–April	Spring
Grishma	May–June	Summer
Varsha	July–August	Rainy
Sharada	September–October	Autumn
Hemanta	November–December	Pre-winter
Shishira	January–February	Winter

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Source for alignment: INDIA PHYSICAL ENVIRONMENT, Geography Class XI, Chapter 4, p.38

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Sources: INDIA PHYSICAL ENVIRONMENT, Geography Class XI, Chapter 4: Climate, p.31; INDIA PHYSICAL ENVIRONMENT, Geography Class XI, Chapter 4: Climate, p.37; INDIA PHYSICAL ENVIRONMENT, Geography Class XI, Chapter 4: Climate, p.38; Exploring Society: India and Beyond, Social Science Class VII, Chapter 4: Climates of India, p.46

2. Mechanism of the Southwest Monsoon (Onset) (intermediate)

To understand the onset of the Southwest Monsoon, we must look at India as a giant thermal engine. During the summer, the sun moves towards the Tropic of Cancer, heating up the Indian landmass and the vast Tibetan Plateau. This heating creates a deep low-pressure area over north and northwest India. Consequently, the Inter-Tropical Convergence Zone (ITCZ)—a belt of low pressure where trade winds meet—shifts northward from the equator to about 20°N-25°N, resting over the Gangetic plain NCERT Class XI, Climate, p.30. This shift acts as a 'vacuum,' pulling in the moisture-laden trade winds from the Southern Hemisphere. As these winds cross the equator, the Coriolis force deflects them to the right, transforming them into the Southwest Monsoon winds.

However, the surface heating is only half the story. The actual trigger or the 'burst' of the monsoon is controlled by high-altitude winds called Jet Streams. For the monsoon to arrive, the Sub-tropical Westerly Jet Stream, which flows south of the Himalayas during winter, must withdraw and shift to the north of the mountains NCERT Class XI, Climate, p.31. Once it clears out, a new wind—the Tropical Easterly Jet (TEJ)—sets in over the peninsula at about 15°N. This sudden shift in the upper atmosphere is what leads to the abrupt and heavy rainfall known as the 'monsoon burst' on the Kerala coast around June 1st Majid Husain, Climate of India, p.14.

The Tibetan Plateau plays a dual role here: it acts as a physical barrier and a high-level heat source. Because of its height, it receives 2°C to 3°C more solar radiation than surrounding areas, heating the atmosphere from above and strengthening the low-pressure system Majid Husain, Climate of India, p.5. This unique combination of surface pressure shifts and upper-air jet movements makes the Indian monsoon onset a sudden, dramatic event rather than a gradual change.

Feature	Pre-Monsoon (Winter/Spring)	Monsoon Onset (June)
ITCZ Position	Near the Equator	20°N - 25°N (Gangetic Plain)
Westerly Jet Stream	South of the Himalayas	North of the Himalayas
Easterly Jet Stream	Absent	Present (over Peninsular India)

Sources: INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Chapter 4: Climate, p.30-31; Geography of India, Majid Husain (McGrawHill 9th ed.), Climate of India, p.5, 14

3. Jet Streams and Western Disturbances (intermediate)

To understand the Indian Monsoon, we must look 10-12 kilometers above the ground at the Jet Streams — narrow bands of fast-moving winds in the upper atmosphere. During the winter, the Subtropical Westerly Jet Stream (STWJ) flows across Asia. However, it encounters a massive physical obstacle: the Himalayas and the Tibetan Plateau. This barrier forces the jet stream to bifurcate (split) into two branches. The northern branch flows north of the Tibetan Plateau, while the southern branch flows south of the Himalayas, directly over Northern India Geography of India, Majid Husain, p.8. This southern branch is the primary reason why North India experiences unique winter weather patterns.

The southern branch of the STWJ acts as a high-speed 'conveyor belt' that brings Western Disturbances into India. These are shallow cyclonic depressions that originate far away in the Mediterranean Sea. As they travel eastward across West Asia, the jet stream steers them toward the Indian subcontinent. These disturbances are a blessing for Indian agriculture; they bring light but essential winter rain and mountain snow, which are vital for the survival of Rabi crops like wheat Environment and Ecology, Majid Hussain, p.52. Without the steering power of these jet streams, the Northwest plains of India would remain largely arid during the winter months.

The role of the jet stream shifts dramatically as summer approaches. As the sun moves towards the Tropic of Cancer, the entire pressure belt system shifts northward. The southern branch of the STWJ, which was anchored south of the Himalayas all winter, suddenly withdraws and jumps to the north of the Tibetan Plateau, usually by early June Geography of India, Majid Husain, p.6. This sudden 'vanishing act' of the westerly jet over the Indian plains creates a vacuum that allows the Tropical Easterly Jet to set in and the Southwest Monsoon to 'burst' onto the Kerala coast INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), p.31.

Feature	Winter Season	Summer (Monsoon) Onset
STWJ Position	Bifurcated (South and North of Himalayas)	Entirely North of the Himalayas/Tibet
Primary Influence	Brings Western Disturbances (Rain for Rabi)	Its withdrawal triggers the Monsoon 'Burst'
Air Flow Type	Westerly (West to East)	Westerly withdraws; Easterly Jet emerges

Sources: Geography of India, Majid Husain, Climate of India, p.8; Environment and Ecology, Majid Hussain, Natural Hazards and Disaster Management, p.52; Geography of India, Majid Husain, Climate of India, p.6; INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Climate, p.31

4. El Niño, La Niña, and the IOD (exam-level)

While the Indian monsoon is a regional phenomenon, it is deeply influenced by teleconnections—global weather patterns that occur thousands of kilometers away. The most significant of these is the ENSO (El Niño Southern Oscillation). Under normal conditions, the Western Pacific is warm, creating a low-pressure zone that helps drive the monsoon winds toward India. However, during an El Niño year, this warm water and the associated rising air (the 'rising limb' of the Walker Circulation) shift eastward toward the central and eastern Pacific. This shift generally suppresses the Indian monsoon, often leading to droughts Physical Geography by PMF IAS, El Nino, La Nina & El Nino Modoki, p.415. Conversely, La Niña—the cooling of the central/eastern Pacific—is usually the monsoon’s best friend, as it strengthens the pressure gradient that pulls moisture into the subcontinent.

However, the Pacific doesn't act alone. The Indian Ocean has its own internal 'oscillation' known as the Indian Ocean Dipole (IOD). The IOD refers to the temperature difference between the western pole (Arabian Sea near the African coast) and the eastern pole (near Indonesia). It typically starts developing in April and reaches its peak in October Physical Geography by PMF IAS, El Nino, La Nina & El Nino Modoki, p.415. To understand how these two systems interact, look at the table below:

Phenomenon	Mechanism	Impact on Indian Monsoon
Positive IOD	Western Indian Ocean is warmer than the Eastern pole. Winds blow East to West.	Favorable: Increases rainfall and can even negate the drying effect of an El Niño.
Negative IOD	Eastern Indian Ocean is warmer. Winds blow West to East (away from India).	Unfavorable: Reduces rainfall; can worsen an El Niño drought.

The most fascinating aspect of these systems is their interaction. You might wonder why India had a normal monsoon in 1997 despite one of the strongest El Niños on record. The answer lies in the Positive IOD that occurred simultaneously, which compensated for the Pacific's moisture deficit Physical Geography by PMF IAS, El Nino, La Nina & El Nino Modoki, p.416. We also track the EQUINOO (Equatorial Indian Ocean Oscillation), which is the atmospheric partner to the IOD's oceanic changes, representing the shifting of air pressure between the Bay of Bengal and the Arabian Sea Physical Geography by PMF IAS, El Nino, La Nina & El Nino Modoki, p.415.

Sources: Physical Geography by PMF IAS, El Nino, La Nina & El Nino Modoki, p.415-416

5. Post-Monsoon Tropical Cyclones (exam-level)

During the months of October and November, as the Southwest monsoon retreats, India enters a transition period. While the land begins to cool, the surrounding seas—particularly the Bay of Bengal—remain exceptionally warm. For a tropical cyclone to form, the sea surface temperature (SST) must generally be above 27°C. In the post-monsoon season, the Bay of Bengal maintains these high temperatures, creating a fertile breeding ground for intense low-pressure systems Majid Husain, Geography of India, Climate of India, p.28. This period is often marked by 'October Heat' on land, where high humidity and temperatures prevail before the onset of winter.

The Bay of Bengal is significantly more active than the Arabian Sea during this time for two primary reasons. First, the remnants of typhoons originating in the Northwest Pacific Ocean often travel across the South China Sea and the Malay Peninsula, re-intensifying as they enter the warm waters of the Bay PMF IAS, Physical Geography, Tropical Cyclones, p.357. Second, the Arabian Sea tends to be cooler in the post-monsoon phase because the vigorous Southwest monsoon winds of the preceding months caused significant upwelling (bringing cold deep-sea water to the surface), which inhibits cyclone formation Majid Husain, Geography of India, Climate of India, p.28.

The path of these cyclones is typically westward or northwestward, making the eastern coast of India a major 'hotspot' for natural disasters. The Coromandel Coast (Tamil Nadu) and the fertile, thickly populated deltas of the Godavari, Krishna, and Kaveri rivers are particularly vulnerable to these destructive storms NCERT Class XI, India Physical Environment, Climate, p.37. These cyclones are the primary source of rainfall for the southeastern peninsula during the retreating monsoon season.

Feature	Bay of Bengal (Post-Monsoon)	Arabian Sea (Post-Monsoon)
Frequency	High (Hotspot)	Low
Temperature	Stays warm (~27°C+)	Cooler due to prior monsoon upwelling
External Input	Receives remnants of Pacific Typhoons	Rarely receives remnants from the Bay
Impact Zone	Odisha, Andhra Pradesh, Tamil Nadu, West Bengal	Gujarat or Maharashtra (less frequent)

Sources: Geography of India (Majid Husain), Climate of India, p.28; Physical Geography (PMF IAS), Tropical Cyclones, p.357; NCERT Class XI, India Physical Environment, Climate, p.37; NCERT Class XI, India Physical Environment, Natural Hazards and Disasters, p.60

6. The Retreating Monsoon: Mechanism and Characteristics (intermediate)

The season of the Retreating Monsoon, occurring during October and November, serves as a critical transition period in the Indian climatic cycle. As the sun begins its apparent movement southward toward the Tropic of Capricorn, the intense heat that sustained the low-pressure trough over the northern plains begins to dissipate. Consequently, this low-pressure system weakens and starts moving southward, causing the moisture-laden Southwest monsoon winds to withdraw from the subcontinent INDIA PHYSICAL ENVIRONMENT, Chapter 4, p.37. The retreat is not instantaneous; it begins in Northwest India by early September and gradually clears the northern parts of the Bay of Bengal by October, finally exiting the Peninsula by mid-December INDIA PHYSICAL ENVIRONMENT, Chapter 4, p.37. During this transition, the weather exhibits a very specific phenomenon known as 'October Heat'. As the monsoon clouds vanish, the skies become clear, allowing the sun to heat the ground intensely. However, because the soil is still saturated with water from the preceding rains, the humidity levels remain very high. This combination of high temperature and high humidity creates an oppressive, sweltering environment during the day, though nights remain cool and pleasant CONTEMPORARY INDIA-I, Chapter 4, p.32. As the low-pressure center shifts from the land to the Bay of Bengal by early November, the nature of rainfall changes. While Northern India stays largely dry, the eastern coast of the Peninsula enters its rainiest phase. The shift in pressure triggers the formation of cyclonic depressions over the Andaman Sea. These cyclones frequently strike the Coromandel coast (Tamil Nadu and Andhra Pradesh), bringing heavy and widespread rain that is vital for the region's agriculture but often destructive due to high wind speeds CONTEMPORARY INDIA-I, Chapter 4, p.32.

Sources: INDIA PHYSICAL ENVIRONMENT, Chapter 4: Climate, p.37; CONTEMPORARY INDIA-I, Chapter 4: Climate, p.32

7. The North-East Monsoon and the Coromandel Coast (exam-level)

As the sun begins its apparent journey toward the southern hemisphere in September, the heat belt that once sat over the northern plains shifts southward. This movement causes the Low-Pressure Trough (the ITCZ) to weaken and migrate toward the Bay of Bengal. Consequently, the moisture-laden Southwest Monsoon winds begin to withdraw, a process that is steady and gradual rather than sudden Geography of India by Majid Husain, Climate of India, p.25. This transition period, occurring during October and November, is characterized by clear skies and a peculiar weather phenomenon known as 'October Heat'—where the combination of high temperatures and high humidity (from the still-moist soil) makes the weather quite oppressive Contemporary India-I, Geography, Class IX, p.32. While most of India experiences dry weather during this 'Retreating Monsoon' phase, the Coromandel Coast (the southeastern coast of India) tells a different story. As the winds reverse direction and blow from the northeast toward the southwest, they are technically off-shore winds (blowing from land to sea) for most of the country, meaning they carry no moisture. However, as these winds cross the Bay of Bengal, they pick up a significant amount of moisture. When they strike the coast of Tamil Nadu and southern Andhra Pradesh, they cause heavy, often torrential, rainfall India Physical Environment, Geography Class XI, p.34. This is why Tamil Nadu, which remains relatively dry during the summer Southwest Monsoon due to being in the rain shadow of the Western Ghats, receives the bulk of its annual rainfall during the winter months.

Feature	Southwest (SW) Monsoon	Northeast (NE) Monsoon
Primary Season	June to September	October to December
Wind Direction	Sea to Land (On-shore)	Land to Sea (Off-shore)*
Main Beneficiary	Most of Mainland India	Coromandel Coast (Tamil Nadu)

*Note: The NE winds become 'on-shore' only for the southeastern coast after crossing the Bay of Bengal. Furthermore, this season is also associated with the movement of cyclonic depressions originating over the Andaman Sea. These cyclones frequently cross the eastern coast of India, particularly the deltas of the Godavari, Krishna, and Kaveri rivers, often causing widespread destruction but also contributing significantly to the region's rainfall Contemporary India-I, Geography, Class IX, p.32.

Sources: Geography of India (Majid Husain), Climate of India, p.25; Contemporary India-I, Geography, Class IX, Climate, p.32; India Physical Environment, Geography Class XI, Climate, p.34

8. Solving the Original PYQ (exam-level)

Now that you have mastered the dynamics of air pressure and the ITCZ shift, you can see how the retreating monsoon acts as a critical transition phase. As the sun begins its apparent movement towards the south, the low-pressure trough over the northern plains becomes weaker, leading to the gradual withdrawal of the Southwest Monsoon. By applying your knowledge of the thermal contrast between land and sea, you can deduce that this is when high pressure begins to establish itself over the cooling landmass, pushing the moisture-laden winds back toward the Bay of Bengal. This process marks the shift from the wet rainy season to the dry winter conditions.

To arrive at the correct answer, (D) October — November, think of the transition season characteristics you just studied: clear skies, rising temperatures, and high humidity, collectively known as "October Heat." While the retreat begins in Northwest India by mid-September, the NCERT Class XI India Physical Environment and NCERT Class IX Contemporary India-I classify these two months as the definitive period of retreat. During this time, the low-pressure center shifts to the Bay of Bengal, giving rise to cyclonic depressions that bring essential rainfall to the Tamil Nadu coast, a specific detail UPSC frequently tests to ensure you understand the spatial impact of the retreat.

It is equally important to eliminate the common traps UPSC sets using the four distinct seasons of the Indian climate. Option (A) January — February represents the Cold Weather Season (Winter), characterized by western disturbances. Option (B) March — April signifies the Hot Weather Season (Summer) where pre-monsoon showers occur. Option (C) June — July is the peak of the Advancing Monsoon, the exact opposite of a retreat. By recognizing that the retreating monsoon is a post-monsoon transition, you can confidently identify October — November as the only period that bridges the gap between the heavy rains of summer and the dry cold of winter.