21.1°C: Coolest September night in Delhi in 15 years

A spell of light rain coupled with gusty winds that continued through the night till early on Thursday meant Delhi residents woke up to a slight chill for the first time this season as the minimum temperature dropped sharply to 21.1 degrees Celsius (21.1°C) – the lowest September mercury in at least 15 years, according to official data.
In other parts of Delhi, the mercury plummeted even further. For instance, the minimum temperature at the India Meteorological Department (IMD)’s Ridge weather station in north Delhi fell to 17.8°C.
An IMD official said the drop was on account of consistent rain and gusty winds. “Delhi saw drizzle throughout the day, till Wednesday night. We also had good wind speed, which helped keep mercury low,” said the official.
The minimum temperature on Thursday at the Safdarjung weather station – considered representative of Delhi – dropped four degrees from the reading on Wednesday (25.1°C), according to IMD data.
Thursday’s minimum was also four degrees below what is considered normal for this time of the year and was the lowest in September since at least 2009 – the earliest IMD has made such data available on its website.
To be sure, it is possible that this record extends even further, but it cannot be verified due to a lack of available data. Despite queries, IMD did not share meteorological data before 2009.
The minimum temperature was 21.4°C at Ayanagar, and 21.6°C at Lodhi Road.
Meanwhile, the maximum temperature on Thursday was 32°C at Safdarjung, as opposed to 29.6°C the day before.
In terms of precipitation, Safdarjung logged 10.2mm of rainfall in the 24 hours till 8.30am on Thursday. No rain was recorded till 5.30pm, according to IMD data. The highest overnight downpour was logged in east Delhi’s Mayur Vihar, which saw 20mm of rain till 8.30am. It was followed by 11mm each at Delhi University and Palam. Isolated drizzle was seen during the day on Thursday, with 0.5mm recorded between 8.30am and 5.30pm at Mayur Vihar and 0.3mm at Palam, data showed.
According to IMD’s forecast, the weekend is likely to be largely rain-free, with the next spell of light rain predicted on September 25 (Wednesday).
Mahesh Palawat, vice-president at Skymet Meteorology said NCR, along with other parts of central, northern and eastern India have been impacted by a depression which has stayed strong through a large part of September. “Prior to Wednesday, the spell of rain last week was also on account of the depression bringing moisture. This has now finally weakened and that means Delhi will get some respite from rain over the next few days,” he said.
“The impact of the depression, which brought rain on Tuesday and Wednesday is over. No active weather system is now prevalent in the region,” said an IMD official, stating the monsoon trough is also further away from Delhi.
Clean air
The overnight rain combined with consistently strong winds of 30km/hr on Thursday also helped improve drastically improve Delhi’s air quality.
Delhi’s 24-hour average air quality index (AQI) stood at 56 (satisfactory) at 4pm on Thursday. In comparison, the AQI on Wednesday was 115 (moderate), according to Central Pollution Control Board (CPCB) data.
Palawat said consistent rain in the past 24 hours has helped Delhi’s air quality, as well as led to the drop in temperature. “We also had good wind speed, particularly at night-time. No rain is likely in the next few days now, as the impact of the depression is now over,” he added.
Forecasts show Delhi’s maximum is likely to rise to 34°C on Friday and remain in this range over the weekend, while the minimum will hover around 23-24°C.
A wet September caps a rainy monsoon
The steady rain throughout the month of September only carries on the larger trend that Delhi has seen this monsoon. Thursday’s 10.2mm rain takes September’s monthly total to 192.5mm, which is already higher than the month’s long-period average (LPA) of 123.4mm.
If Delhi crosses 200mm in monthly rainfall in September, this will be the fourth consecutive month where Delhi has crossed 200mm.
The Capital logged 243.4mm in June this year, largely aided by a 24-hour spell of “very heavy” rain on June 28, when 228.1mm was recorded on the very first day monsoon officially arrived. This pushed June’s rainfall figure to over three times its monthly average of 74.1mm.
In July, Delhi received mostly scattered light rain, but still managed to log 203.7mm through the month, marginally short of the long-period average of 209.7mm.
In August, Delhi again saw multiple spells of heavy rain, taking the total rainfall through the month to 390.3mm – 67% higher than the monthly average of 233.1mm. In August, the city saw rain on 26 out of 31 days, making it the wettest August since 2010, when 455.1mm was recorded, according to IMD data.
So far, this month is the wettest September since 2021, when 413.3mm was recorded.
In total, the city has now seen 1,029.9mm of precipitation through the four months of June to September (what IMD officially considers the monsoon season in Delhi). The long-period average for monsoon in Delhi is 640.3mm.
Despite a very dry start to the year, which saw just 44.7mm rainfall recorded in the first five months, Delhi’s total yearly rainfall now lies in the excess – it had crossed its annual average rainfall mark of 770.4mm in August itself, and with four months to spare in the year.
In total, Delhi has logged 1074.6mm rainfall so far in 2024, making it the wettest year since 2021, when 1,169.7mm rain was recorded.
Thursday was also the 14th day of rain this September. The last time Delhi recorded more rainy days in the month was 2021, when rain was recorded on 18 days in the month. Normally, the southwest monsoon withdraws from Delhi around September 25.