Monsoon set to arrive in Delhi today

As of Wednesday, the northernmost boundary up to which monsoon has advanced stands at Barmer, Jodhpur, and Jaipur in Rajasthan; Agra, Rampur, and Bijnor in Uttar Pradesh; Karnal in Haryana, and Halwara in Punjab.

While the IMD also sounded a yellow alert in Delhi-NCR for Wednesday, trace rainfall was logged in Delhi-NCR during the day. Northeasterly winds prevailed with wind speed up to 17 kmph over Delhi in the past 24 hours, said the weather office.

In its forecast for Thursday, the IMD anticipated generally cloudy skies with light to moderate rainfall, thunderstorms, lightning, and gusty winds ranging from 30 to 40 km/h. This rainfall is likely to significantly reduce the temperature in the Capital, bringing maximum daytime highs down to approximately 33-35°C and nighttime lows to around 26°C.

Onset og monsoon in Delhi over the years.

Historically, the onset of monsoon in Delhi – from 1960 to 2024 – has demonstrated significant variability, generally ranging between mid-June and mid-July. Early arrivals occurred in 1961 (June 9) and 2013 (June 16), while the most delayed recorded onset was in 2002 (July 19).

Despite these fluctuations, the long-term average onset date has hovered around June 27, making this year’s forecasted arrival date consistent with the historical average, but notably earlier than the recent past, including June 28 onset in 2024 and June 30 in 2022.

Meteorological precursors signalling the arrival of monsoon include increased humidity levels, often exceeding 85-90 per cent, resulting in muggy weather conditions. This has been observed in Delhi over the past few days, as humidity levels oscillated along this range, the IMD stated. The humidity levels remained high on Wednesday, between 77% to 83%.

The easterly winds prevailing in the Capital are also instrumental in carrying moisture inland, enhancing conditions favourable for rainfall. Further, sporadic pre-monsoon showers and thunderstorms have occurred recently, weakening the summer heat, which, as a result, has yielded below normal day temperatures.

Delhi’s average Air Quality Index (AQI), meanwhile, was recorded at 132, in the “moderate” category. It was 95, in the “satisfactory” category, on Tuesday.

The maximum temperature was recorded at 34.9°Celsius on Wednesday, around two notches below normal. The minimum temperature was a notch above normal at 29.6°Celsius.