The Science of a Slow Goodbye
The monsoon's withdrawal isn't like flipping a switch. It’s a gradual process driven by large-scale atmospheric changes. As the sun moves southward, the intense low-pressure system over the Indian subcontinent begins to weaken. The moisture-laden southwesterly
winds that define the monsoon lose their strength, causing them to retreat. This withdrawal officially begins when rainfall ceases over an area for a sustained period and anticyclonic circulation, which brings dry air, establishes in the lower levels of the atmosphere. According to the India Meteorological Department (IMD), this process typically starts in the extreme northwestern parts of the country, like West Rajasthan, and then slowly progresses southeastward over several weeks. This year, the withdrawal is expected to start around its normal date of September 17.
A Below-Normal Farewell for 2026
This year's monsoon season has been influenced by a strengthening El Niño pattern in the Pacific Ocean, which is often linked to suppressed rainfall in India. Following a deficient August, the IMD has forecast that September rainfall is also likely to be below normal for the country as a whole. This points toward the monsoon season ending with a cumulative rainfall deficit. However, this doesn't mean rain will stop everywhere. Some areas in Northwest, Northeast, and parts of Peninsular India might still see normal to above-normal rainfall, even as other regions dry out. This below-average forecast is also expected to keep temperatures higher than usual, with most parts of the country likely to experience above-normal maximum temperatures this month.
What to Expect: A Regional Outlook
Because the withdrawal is a staggered, six-week process, different cities will experience September very differently.
In the North (Delhi): The monsoon's retreat here often brings clearer skies and a welcome drop in rainfall. However, this can also lead to a temporary rise in daytime temperatures before the pleasant autumn weather settles in. While the overall trend is drier, sporadic thunderstorms can still occur.
On the West Coast (Mumbai): The monsoon lingers longer here. Residents can expect a period of high humidity and uncomfortable warmth, often called the 'October heat,' which can start in September. While the torrential downpours become less frequent, light to moderate rain showers are still common.
Down South (Chennai): For the southeastern coast, the end of the southwest monsoon is just a prelude. This region gets most of its annual rainfall from the northeast monsoon, which arrives later in the year, between October and December. September acts as a transitional month, with subdued rainfall expected for the next week but the potential for thunderstorms.
In the East (Kolkata): Eastern India is one of the last regions to see the monsoon withdraw. A low-pressure system over the Bay of Bengal can continue to bring moderate rain and thunderstorms to cities like Kolkata well into September.
More Than Just Rain and Heat
The transition from the wet season to the dry season has widespread implications. For farmers, the timing of the final rains is critical for maturing kharif crops and for the soil moisture needed to plant winter rabi crops. A drier-than-normal September can increase concerns about crop yields. The retreating monsoon is also the primary season for cyclonic activity in the Bay of Bengal. As the low-pressure system shifts over the water, it can spawn tropical cyclones that primarily threaten the eastern coast, with October and November being the most active months.
