Delhi's air quality index fell from 363 to 78 after 61.4 mm of rain drenched the city on Friday, marking the wettest October day in four years.
The deluge was engineered by a western disturbance over the Himalayas, a cyclonic swirl in South Punjab, and winds from the Bay of Bengal carrying remnants of Cyclone Arnab, says Mahesh Palawat, vice‑president of meteorology at Skymet Weather Services.
The sudden rainfall cooled the capital by 4 °C, with Safdarjung's daytime high hitting 25.4 °C—5.6 °C below the October norm—while minimum temperatures hovered between 15.4 °C and 17.2 °C.
The India Meteorological Department forecasts temperatures to remain in the 24–26 °C range on Saturday before climbing toward the 28–31 °C bracket, with skies clearing by early November; pollution levels are expected to rebound to the poor category within days.
A resident in Lajpat Nagar, who had been coughing for weeks, said the sudden clear air felt like a breath of fresh oxygen, but he fears it will be a fleeting relief.