Hot nights, hotter days: Why Delhi has been sweltering this September

The last time the city recorded a higher September minimum was in 2019, when 29.6°C was reported on September 12 of that year.

The Capital also reeled under daytime heat, with Monday’s maximum recorded at 37.5°C, which is around three degrees above normal.

A day before, the maximum settled at 38.1°C, making it the hottest September day in two years. The last time the maximum was higher was on September 5, 2023, at 38.6°C.

What’s behind the heat?

Though Northwest India saw 42% surplus rainfall this September, the Southwest monsoon withdrew from Delhi on September 24 — its earliest retreat since 2002. The absence of rain-bearing systems since then has reinforced the hot spell.

After the early withdrawal of the monsoon, the unusually high temperatures have been due to a mix of clear skies allowing more daytime heating and high humidity levels that slowed night-time cooling.

With the relative humidity oscillating between 54% and 85% through the day, moisture in the air acted like a blanket, trapping heat near the surface. Easterly winds kept moisture levels elevated, further curbing relief at night.

Over the past 24 hours, easterly winds with speeds up to 20 kmph have prevailed over the city, as per the IMD. The wind shift has also helped air quality by blocking smoke from farm fires up north.

According to Indian Agricultural Research Institute (IARI) data, 130 stubble-burning incidents have been reported so far this season, with 90 in Punjab, 27 in Uttar Pradesh, 6 each in Haryana and Madhya Pradesh, and 1 in Rajasthan. These have started to emerge since September 15, and their impact on Delhi’s air quality remains minimal.

Delhi’s 24-hour average Air Quality Index (AQI) improved for the second day in a row as it stood at 120 at 4 pm on Monday, improving from Sunday’s 139 AQI. Meanwhile, Saturday’s 169, was also the city’s highest since June 13.

Forecasts by the Indian Institute of Tropical Meteorology (IITM) suggest the air quality is likely to remain “moderate” through the week.

Will it get cooler?

Meanwhile, the temperature conditions are expected to ease out, as per the weather department.

The India Meteorological Department (IMD) has forecast generally cloudy conditions with light rain or drizzle on Tuesday and Wednesday.

Cloudy weather is likely to persist until October 5, gradually bringing down temperatures, with the minimum expected to dip to around 23°C and the maximum to about 32°C.