The Monsoon's Slow Retreat
Throughout June, July, and August, the southwest monsoon brings cloud cover and rain, which, despite the humidity, helps keep a lid on daytime temperatures. By September, this system begins its gradual withdrawal, starting from the northwestern parts
of India and moving southeast. The India Meteorological Department (IMD) has indicated that the 2026 monsoon withdrawal could begin around the middle of the month. As the monsoon trough weakens, the dense cloud cover that acted as a natural sunshade dissipates. This transition from a cloudy, rainy season to a clearer, drier one is the first key ingredient for the spike in perceived heat.
Why Clear Skies Feel Hotter
While clouds can trap heat, they are more effective at blocking incoming solar radiation during the day. As they disappear in September, the sun's rays beat down on the land and water bodies more directly. This increased solar insolation heats the surface of the earth, which in turn heats the air. Consequently, the actual air temperature, the number you see on a thermometer, begins to climb. After months of being moderated by rain and clouds, this return of intense, direct sunshine can make daytime temperatures feel surprisingly high, often returning to near-summer levels even as the calendar moves towards autumn.
The Humidity Trap
This is the most crucial part of the puzzle. The monsoon doesn't just disappear overnight; it leaves behind a significant amount of moisture in the soil and the lower atmosphere. As temperatures rise from the clear skies, this residual moisture evaporates, pushing up the relative humidity. Our bodies cool down primarily through the evaporation of sweat. But when the air is already saturated with water vapour, sweat can't evaporate efficiently. Instead, it clings to the skin, making you feel sticky, uncomfortable, and much hotter than the actual temperature suggests. This phenomenon is measured by the 'heat index' or 'feels like' temperature, which can be several degrees higher than the air temperature during this period.
A Preview of 'October Heat'
This uncomfortable combination of rising temperatures and high humidity in late September is the precursor to a well-known phenomenon: 'October Heat'. This term describes the oppressive, muggy conditions experienced across many parts of India, particularly the northern plains, as the southwest monsoon fully retreats. While the name points to October, the conditions that create it begin to build as soon as the monsoon starts its withdrawal in September. The clear days allow for strong sunshine, while the moisture-laden ground ensures the humidity remains uncomfortably high, setting the stage for the peak of this transitional heat in the following weeks.
What This Means for 2026
Forecasts for the 2026 monsoon season add another layer to this story. The IMD has projected a below-normal monsoon for the year, influenced by developing El Niño conditions. A drier-than-usual monsoon could mean that while there's less overall rainfall, the subsequent withdrawal phase might still be marked by this characteristic heat. The ground will still hold moisture, and the quicker return to prolonged clear skies could make the heat-humidity combination feel particularly intense. This period serves as a critical reminder that the end of the rains doesn't signal an immediate switch to cool, pleasant weather; instead, it ushers in a unique 'second summer' that demands just as much attention to hydration and avoiding exertional heat.
