October logs ‘excess’ rains in one day

Delhi experienced heavy rains on October 3, surpassing the monthly average, with forecasts for continued rainfall, improving air quality.

With the intense post-monsoon showers that lashed the capital on Tuesday, October has already logged ‘excess’ rains in one day, according to the India Meteorological Department (IMD).

A tree gets uprooted during heavy rain on Tilak Marg on Tuesday. (Arvind Yadav/HT Photo)

Safdarjung, the city’s base station for weather, received 37.8mm of rainfall between 8.30am and 5.30pm. Since the IMD counts rain on the last day of the month after 8:30 am as rainfall for the first day of the next month, Delhi has crossed the long-period average (LPA) for rain in October of 15.1mm — making this the sixth straight month since May to record excess rain this year.

Last year, October saw zero rainfall. While October 2023 recorded 5.4mm of rain, October 2022 saw 128.4mm of rainfall — the highest for October in the last decade.

Tuesday’s weather did not match the IMD forecast, which had initially predicted only very light rain and drizzle in the city. As a result, no colour-coded alerts had been issued for Tuesday a day earlier. A ‘yellow’ alert was issued at 11 am on Tuesday, which was upgraded to an ‘orange’ alert at 11.55am.

At a press conference, IMD officials said a combination of weather systems led to moisture being drawn in towards the National Capital Region (NCR) from both the Arabian Sea and the Bay of Bengal.

“A well-marked low-pressure area lies over the Gulf of Kutch. A trough runs from this low-pressure area to Southeast Uttar Pradesh. At the same time, another trough runs from this low pressure area to Northwest Rajasthan in the lower tropospheric levels,” said IMD scientist Krishna Mishra, explaining that the rain could be attributed to these troughs facilitating moisture.

The IMD has forecast more rain in the city in the coming days. It has said generally cloudy skies will persist on both Wednesday and Thursday. While a spell of light rain is likely on Wednesday, one to two spells of very light rain are likely on Thursday. The IMD has also forecast light rain on October 6.

On Tuesday, the station in Palam recorded 21.8mm of rain, Lodhi Road 29.8mm, Ridge 52.9mm, Ayanagar 72.6mm, Raj Ghat 40.5mm, Pusa 36mm and Mayur Vihar 35mm.

This year, the retreat of the monsoon was declared on September 24, the earliest in Delhi since 2002, when it departed on September 20. Last year, the monsoon had withdrawn on October 2.

Overall, this monsoon season, Safdarjung logged an excess of around 41%, receiving 902.6mm against its normal of 640.4mm. Delhi, as a whole, received an average of 736.2mm — an excess of 37% over the normal mark of 536.3mm. IMD counts rainfall data from June till September as monsoon rainfall.

The month of September ended with 136.1mm, over the monthly normal of 123.5mm. Excess rains have been dominant in the region since May. This May was the wettest ever on record with 186.4mm of rainfall, over six times the normal average of 30.7mm. In June, Delhi recorded 107.1mm of monthly rainfall, an excess of 45% over the LPA of 74.1mm. In July, Delhi received 259.3mm of rainfall, which was 24% more than the LPA of 209.7mm. August meanwhile was the wettest in 15 years, with 400.1mm logged— an excess of 72% over the LPA of 233.1mm.

There was marginal improvement in Delhi’s air quality, with the 24-hour average air quality index (AQI) recorded at 117 (moderate) at 4 pm. It was 120 (moderate) a day earlier.

Forecasts by the Centre’s Air Quality Early Warning System (EWS) for Delhi shows the rain is likely to have a washout effect, with the AQI dipping to ‘satisfactory’ category by Wednesday.