The Gradual Goodbye of the Monsoon
The Southwest Monsoon doesn't just switch off like a light. Its retreat is a gradual, staggered process that takes weeks. The withdrawal typically begins from the northwestern parts of India, like Rajasthan, around mid-September. From there, the line
of withdrawal slowly moves southeast across the country. This means that while northern regions might start experiencing dry, post-monsoon weather, central and eastern India can still be very much in the thick of rainy conditions. This extended farewell tour is where the Bay of Bengal takes center stage.
The Bay of Bengal: A Monsoon Engine
Think of the Bay of Bengal as a giant, warm basin that fuels the monsoon. Its high sea surface temperatures, often exceeding 28°C, provide the two essential ingredients for rain: heat and moisture. This warmth helps create low-pressure areas, which are the seeds of monsoon rainfall. Throughout the season, the Bay continuously sends moisture-laden winds towards the Indian subcontinent, but its role becomes especially critical in September.
The Power of Low-Pressure Systems
In September, the Bay of Bengal is known for churning out a series of low-pressure systems or depressions. These are essentially large areas of atmospheric circulation that draw in moist air from the sea. As these systems form over the water, they gather strength and typically move in a west-northwesterly direction, travelling inland over states like Odisha and West Bengal and then moving across central and northern India. They act like meteorological magnets, pulling the monsoon trough—a belt of low pressure—southwards and keeping the rains active. Recent forecasts from the India Meteorological Department (IMD) confirm that such systems continue to influence weather patterns, bringing rain to eastern and central parts of the country well into September.
Reviving and Sustaining the Rains
Without these systems from the Bay, the monsoon's withdrawal would be much faster and drier. These low-pressure areas are responsible for reviving rainfall activity, often leading to heavy downpours in central and eastern India long after the monsoon has weakened in the north. They can stall or even reverse the monsoon's retreat, ensuring regions get a final, crucial spell of rain. This September rainfall is vital. It replenishes reservoirs and, critically, provides the necessary soil moisture for farmers preparing to plant winter crops like wheat and chickpeas.
What It Means for This Year
Even in years when the monsoon seems to be weakening or a deficit is predicted, a single potent low-pressure system from the Bay can dramatically alter the picture for many regions. As of early September 2026, active systems originating in the Bay have been responsible for keeping the monsoon vigorous over eastern, central, and northern states, with heavy rain forecast for areas like Uttar Pradesh, Bihar, and Madhya Pradesh. These September rains demonstrate that the monsoon's finale is not a gentle fade-out but a dynamic process driven by the powerful influence of the Bay of Bengal.
