Withdrawal of the Southwest Monsoon: How Does IMD Determine When the Monsoon Retreats from India?

The withdrawal of the southwest monsoon has begun over India. On 19 September 2026, the India Meteorological Department (IMD) declared the withdrawal of the southwest monsoon from some parts of West Rajasthan, marking the beginning of the seasonal retreat of the monsoon.

The arrival of the southwest monsoon is one of the most closely watched weather events in India. But its departure is equally important. The withdrawal of the monsoon marks a major transition in India's atmospheric circulation, gradually bringing an end to the southwest monsoon season and preparing the atmosphere for the post-monsoon season.

But how does the India Meteorological Department determine that the southwest monsoon has started withdrawing? IMD uses a set of meteorological and synoptic criteria to identify the beginning of withdrawal and then monitors its progressive retreat across the country. With the southwest monsoon beginning its withdrawal in 2026, this is a good opportunity to understand how monsoon withdrawal is determined, what the normal withdrawal dates are, and how the process varies from year to year.

How Does IMD Declare the Beginning of Withdrawal?

According to IMD's operational definition, withdrawal from the extreme north-western parts of the country is not attempted before 1 September. After 1 September, three major synoptic features are considered for the first withdrawal:

  1. Cessation of rainfall activity over the area for a continuous five days.
  2. Establishment of an anticyclone in the lower troposphere, at 850 hPa and below.
  3. Considerable reduction in atmospheric moisture, inferred from satellite water-vapour imagery and tephigrams.



Figure 1. Flowchart illustrating the major criteria used by IMD for declaring the withdrawal of the southwest monsoon from the extreme north-western parts of India. Note: The infographic accompanying this article is intended for educational and awareness purposes and does not represent an official IMD publication.

All three provide complementary information about the weakening and retreat of the monsoon circulation. Let us now understand what these three major synoptic features really mean.

Cessation of Rainfall Activity: The first requirement is that rainfall activity should cease over the area for five continuous days. This does not simply mean that there is no rainfall on one particular day. The criterion looks for a sustained change in rainfall activity, indicating that the monsoon influence is weakening.

Establishment of an Anticyclone: An anticyclone must become established in the lower troposphere, at 850 hPa and below. An anticyclone is a region of relatively high atmospheric pressure associated with descending air and generally more stable and drier conditions. Its establishment is therefore an important indicator that the atmospheric circulation characteristic of the southwest monsoon is weakening over the region.

Reduction in Atmospheric Moisture: The third criterion is a considerable reduction in moisture content. This is assessed using observations such as satellite water-vapour imagery, and atmospheric soundings or tephigrams. The reduction in moisture provides evidence that the humid monsoon air mass is being replaced by a comparatively drier air mass. Thus, the declaration of withdrawal is based on a combination of rainfall, circulation and atmospheric moisture, rather than rainfall alone.

Once withdrawal begins from the extreme northwest, IMD continues to monitor the retreat of the monsoon across the country. For further withdrawal, IMD considers:

  • spatial continuity of the withdrawal,
  • reduction in atmospheric moisture as seen in water-vapour imagery, and
  • prevalence of dry weather for five days.

Therefore, the withdrawal line does not simply jump from one region to another. It is monitored as a progressive spatial transition.

The southwest monsoon normally begins withdrawing from northwestern India, particularly the Rajasthan region, before progressing toward other parts of the country. This is associated with the seasonal reversal of the atmospheric circulation and the gradual establishment of drier conditions over northwest India. The northwest is also climatically the first major region to experience the weakening of the monsoon circulation as the summer land–sea thermal contrast changes. This is why the first withdrawal is normally observed over west Rajasthan, while the monsoon continues to influence central, southern and northeastern parts of India.

What Is the Normal Date of Monsoon Withdrawal?

Just as IMD has normal dates for monsoon onset and advance, it also has normal climatological dates for withdrawal. The revised normal withdrawal dates are based on operational withdrawal dates during 1971–2019. Under these revised normals, withdrawal from northwest India begins around 17 September, followed by progressively later withdrawal dates over other parts of the country.


Figure 2. Normal dates of withdrawal of the southwest monsoon over India. Withdrawal generally begins over northwest India in September and progresses across the country during September and October. [Source: IMD]

The normal withdrawal dates shown on the IMD map illustrate this progression:

  • 17 September – beginning over parts of northwest India
  • 20–25 September – further withdrawal over Rajasthan and adjoining areas
  • 30 September–5 October – withdrawal expands across northwestern and central India
  • 10 October – withdrawal progresses into more parts of central and eastern India
  • 15 October – withdrawal reaches most of the remaining country, including the southern peninsula.

These are climatological normal dates, not fixed dates on which withdrawal must occur every year. This year's withdrawal provides a timely example. 

The Withdrawal of the 2026 Southwest Monsoon

On 19 September 2026, IMD declared that the southwest monsoon had withdrawn from some parts of West Rajasthan. The normal withdrawal date for this region is 17 September, meaning that the withdrawal in 2026 began about two days later than normal. IMD also indicated favourable conditions for further withdrawal from some more parts of Rajasthan and parts of Punjab, Saurashtra and Kutch during the following 3–4 days. The withdrawal line shown on the latest IMD map passes through parts of western Rajasthan, illustrating that the retreat has only just begun.


Figure 3. Figure 3. Withdrawal of the southwest monsoon over India as on 19 September 2026. The red lines represent the normal dates of withdrawal, while the blue line indicates the actual withdrawal boundary. As of 19 September, the southwest monsoon had withdrawn from some parts of West Rajasthan.


Just as the Northern Limit of Monsoon (NLM) is used to monitor the northward advance of the southwest monsoon, the withdrawal boundary is used to monitor its retreat. The withdrawal line represents the approximate southern/eastern boundary of the region from which the southwest monsoon has withdrawn. As withdrawal progresses, this line generally moves southward and southeastward across India. This provides meteorologists and the public with a simple way of visualising the changing spatial extent of the southwest monsoon.

The final stage of withdrawal has an additional condition. According to IMD, withdrawal from the southern peninsula and hence from the entire country is declared only after 1 October, when the circulation pattern indicates a change from the southwesterly wind regime. This is important because the southern peninsula has a different seasonal rainfall regime. Even after the southwest monsoon withdraws from much of northern and central India, parts of southern India can continue to receive rainfall.

The withdrawal of the southwest monsoon is also closely associated with the transition toward the northeast monsoon over the southern peninsula. During the post-monsoon transition, the atmospheric circulation over the Indian subcontinent and surrounding seas undergoes a major seasonal reversal. Over southern peninsular India, particularly Tamil Nadu and adjoining areas, the northeast monsoon becomes an important source of rainfall during October–December. Thus, the withdrawal of the southwest monsoon is not simply the end of one season—it is part of a broader seasonal transition in the Indian climate system.

2024 vs 2025 Southwest Monsoon

In 2024, withdrawal of the southwest monsoon from northwest India began on 23 September, compared with the normal date of 17 September. The withdrawal subsequently progressed across the country, with the southwest monsoon finally withdrawing from the entire country on 15 October 2024. IMD attributed some of the delay in the initial withdrawal to the influence of a low-pressure system over the Bay of Bengal.

In contrast, the southwest monsoon withdrawal in 2025 began on 14 September, about three days earlier than the normal date of 17 September. The retreat subsequently progressed across the country, with the southwest monsoon withdrawing from the entire country on 16 October 2025.

Figure 4. Figure 4. Comparison of the withdrawal of the southwest monsoon over India in 2024 and 2025. The red lines indicate the normal dates of withdrawal, while the blue lines show the actual withdrawal dates. The southwest monsoon withdrew from the entire country on 15 October 2024 and 16 October 2025, respectively. [Source: IMD]


Why Doesn't the Monsoon Withdraw at the Same Speed Every Year?

The withdrawal of the monsoon is not a smooth or uniform process. Some years witness a relatively rapid retreat, while in other years the withdrawal can become slow or temporarily stall over particular regions. This variability is influenced by several atmospheric and oceanic factors, including:

  • persistence of rainfall-producing weather systems,
  • low-pressure systems over the Bay of Bengal,
  • atmospheric circulation patterns,
  • moisture availability,
  • upper- and lower-tropospheric winds,
  • land–sea thermal contrast, and
  • large-scale climate variability.

Consequently, the actual withdrawal dates can differ considerably from the normal climatological dates. The last few years (e.g. 2024 and 2025) provide useful examples of this year-to-year variability.

Conclusion

The withdrawal of the southwest monsoon is a carefully monitored atmospheric transition. What may appear to be a simple reduction in rainfall is, in fact, assessed using multiple indicators of changing atmospheric conditions. The first withdrawal requires the combined evidence of persistent cessation of rainfall, establishment of an anticyclone in the lower troposphere, and a substantial reduction in atmospheric moisture. Once withdrawal begins, IMD tracks its spatial progression using rainfall, moisture and circulation characteristics.

On 19 September 2026, the southwest monsoon began its withdrawal from some parts of West Rajasthan—just two days after its normal withdrawal date of 17 September. But this is only the beginning of the retreat. Over the coming weeks, the withdrawal line will progressively move across the country as the atmospheric circulation changes and the southwest monsoon gradually gives way to the post-monsoon season, including the northeast monsoon over southern peninsular India.

The southwest monsoon is a dynamic seasonal circulation system whose onset, advance, withdrawal and transition are governed by evolving atmospheric and oceanic conditions. Thus, the withdrawal of the southwest monsoon represents a reorganisation of the atmospheric circulation over the Indian region as the climate system transitions from the summer monsoon to the post-monsoon season.

Featured Articles:

(i) El Niño, La Niña and the Indian Monsoon: A Climate Story from the Pacific Ocean to India

(ii) A Possible El Niño in 2026: What It Could Mean for the Indian Monsoon

(iii) Why Did the 1997 and 2015 Super El Niño Events Produce Different Indian Summer Monsoons?

(iv) El Niño Does Not Always Mean “No Rain” During the Monsoon: Can Better Water Management Reduce Its Impacts?

(v) What Does IMD's Probabilistic Monsoon Forecast Really Mean?

(vi) How IMD Declares the Monsoon Onset over Kerala and Monitors Its Advance Across India


Disclaimer: The views and interpretations presented in this blog are solely those of the author and are intended for educational and science communication purposes. They do not necessarily represent the official views, policies, forecasts, or positions of the India Meteorological Department (IMD) or any other organization with which the author is affiliated.









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