May 30 brought Delhi a satisfactory AQI reading of 85, the cleanest day of any May since 2023. It followed widespread rain and strong winds, and it capped a month that was strange on both counts: hot, and unusually clean.
Start with the heat. Delhi’s average maximum for May was 39.7 degrees Celsius and the average minimum was 25.8. Only 2024 was hotter among recent Mays, with averages of 41.7 and 26.5 degrees Celsius. A heatwave ran from May 18 to 21, and in some parts of the city the maximum went past 46 degrees Celsius.
Rain totalled 17.61 mm.
Why the weather swung
Mahesh Palawat of Skymet Weather pointed to several things working at once: western disturbances, induced cyclonic circulations over Rajasthan and neighbouring areas, and moisture-laden winds from the Bay of Bengal. Experts said the early disturbances triggered pre-monsoon activity and kept the first half of the month cool. When those systems faded, temperatures climbed fast. Another strong spell of pre-monsoon weather arrived near month’s end.
By then, said Palawat, thunderstorms, rain and gusty winds had spread across the capital and eased the heat over the last few days.
The air quality numbers
The Centre for Research on Energy and Clean Air (CREA) found an average AQI of 161 through May 29. No May has been lower since 2021, when the figure was 144. For comparison, May 2025 averaged 170 and May 2024 averaged 223.
The daily tally from May 1 to May 29 reads three satisfactory days, 20 moderate and six poor. Delhi had no very poor or severe days at all. In May 2021 the split was six satisfactory, 22 moderate and three poor.
Experts credited rain and intermittent strong winds with scattering pollutants. Dust carried in from Rajasthan produced several dust storms and dragged air quality down at points, but intense local rainfall washed particulate matter out of the air.
What comes next
Palawat does not expect a heatwave in the first week of June. Temperatures are forecast to rise gradually from June 1, as the present rainy spell loses strength and moves off.
