Hottest in two years, cleanest air in five: Delhi's May of extremes

New Delhi: The weather in Delhi has experienced extremes this month, with the city recording its hottest May in two years while also enjoying its cleanest air in five years. This unusual weather includes heatwaves, unseasonably warm nights, and thunderstorms.

Delhi's average maximum temperature for May reached 39.7 degrees Celsius, with the average minimum temperature at 25.8 degrees Celsius.

The last hotter May occurred in 2024, when the average maximum and minimum temperatures were 41.7 degrees Celsius and 26.5 degrees Celsius, respectively.


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Heatwave conditions were noted from May 18 to 21, with maximum temperatures exceeding 46 degrees Celsius in some areas of the city. Overall, Delhi received 17.61 mm of rainfall during the month.

The city also experienced unusually warm nights in May, with minimum temperatures hitting 32.8 degrees Celsius on May 26 and 31.9 degrees Celsius on May 21-among the highest nighttime temperatures recorded in the city in the last 14 years, according to data from the India Meteorological Department (IMD).

The IMD defines a heatwave as a situation where the maximum temperature exceeds 40 degrees Celsius and is 4.5 to 6.4 degrees Celsius above normal.

A warm night is declared when the maximum temperature remains at 40 degrees Celsius or higher, and the minimum temperature is also 4.5 to 6.4 degrees Celsius above normal.

Mahesh Palawat of Skymet Weather attributed the month's fluctuating weather to a combination of western disturbances and induced cyclonic circulations over Rajasthan and adjoining areas, and moisture-laden winds from the Bay of Bengal.

Experts said frequent western disturbances and associated weather systems led to early pre-monsoon activity, leading to low temperatures during the first half of May.

As these systems weakened, temperatures rose sharply and heatwave conditions developed across parts of Delhi before another spell of strong pre-monsoon activity returned towards the end of the month, they said.

Palawat mentioned that thunderstorms, rain and gusty winds intensified during the latter part of May, bringing widespread weather activity across the capital and providing relief from the intense heat over the past few days.

Despite the hotter conditions, Delhi recorded its cleanest AQI in May in about five years.

An analysis by the Centre for Research on Energy and Clean Air (CREA) showed that the capital's average AQI was 161 until May 29, the lowest for the month since 2021, when it was 144.

On Saturday, May 30, Delhi recorded a satisfactory AQI of 85, following widespread rainfall and strong winds. This represented the cleanest air quality day in May since 2023 and the fourth satisfactory air quality day this month.

Experts noted that rainfall and intermittent strong winds played crucial roles in dispersing pollutants.

While dust transported from Rajasthan caused several dust storm events and deteriorated air quality, localised intense rainfall helped wash out particulate matter and improve the overall air quality in the city.

Data showed that from May 1 to May 29, Delhi experienced three satisfactory days, 20 moderate days, and six poor days, with no very poor or severe air quality days.

In comparison, May 2021 recorded six satisfactory days, 22 moderate days and three poor days, while the monthly average AQI stood at 144. May 2025 recorded an average AQI of 170 and May 2024 recorded 223.

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Looking ahead, Palawat stated that no heatwave conditions are expected in the first week of June.

However, temperatures are forecasted to gradually rise from June 1 as the current spell of rain activity weakens and shifts away from the region.