Two weather systems coinciding brought heavy rainfall to Delhi-NCR at the fag end of the monsoon season, after what was a mostly dry August and September.
The heavy rainfall spell that began on Thursday and extended into Friday was only the second such heavy spell for the southwest monsoon season in Delhi so far. The first such heavy spell was recorded when the monsoon hit Delhi on June 30.
Between 8.30 am on Thursday and 8.30 am on Friday, the Safdarjung weather station, which provides a marker for the city, recorded 72 mm of rainfall. In the past 13 years, the highest 24-hour rainfall amount at Safdarjung in September was 117.7 mm on September 2, 2021. The 24-hour rainfall at Safdarjung in September has crossed the 70 mm mark in 2017 as well, when 77.8 mm of rainfall was recorded on September 23.
India Meteorological Department (IMD) scientists pointed out that the weather stations at Palam and Aya Nagar recorded the highest amounts of rainfall in the city. The Palam weather station recorded 102 mm between 8.30 am on Thursday and 8.30 am on Friday, while Aya Nagar recorded 106.2 mm.
The city had recorded a large deficit in rainfall in August and in September till the current rainfall spell hit the National Capital Region. The Safdarjung weather observatory had a rainfall deficit of around 53% as of September 19. This deficit was wiped off with the rainfall recorded on Thursday and Friday. Till 8.30 am on Friday, Safdarjung had recorded 130.5 mm of rainfall in September, which is an excess of 16% for the month, when compared to a normal of 112.8 mm till September 23.
According to IMD scientists, Delhi only witnesses around one heavy rainfall spell during the monsoon season. “The normal number of heavy rainfall spells during the monsoon at the Safdarjung weather observatory is around one,” said R K Jenamani, scientist, IMD. “Last year, there were more – six at Safdarjung and around eight at Palam,” he added.
Till 5.30 pm on Friday, Safdarjung recorded 8 mm of rainfall, while Palam recorded 30.3 mm of rain.
This spell is likely to end and dry weather could return from the night of September 25 or morning of September 26 onwards, Jenamani said.
Jenamani explained that the rainfall is on account of the remnants of a low-pressure system and a Western Disturbance. According to an IMD update issued Friday evening, a cyclonic circulation lies over northwest Madhya Pradesh and the neighbourhood.
“The maximum amount of rainfall in the past 24 hours was in the Faridabad-Ballabgarh area, which saw 180 mm. An intense circulation is active around 200 km to the southeast of Delhi. This extends up to the mid tropospheric levels. A Western Disturbance is also interacting with this, and there is a lot of moisture supply from the Arabian Sea,” he said.
Rainfall between 64.5 mm and 115.5 mm is considered to be ‘heavy’, according to the IMD.
In September 2021, there were three days when heavy rainfall was recorded at Safdarjung. There was no such heavy rainfall spell in September 2020, 2019 and 2018. In September 2017, there were two days when Safdarjung recorded heavy rainfall.
Moderate rainfall and heavy rainfall in one or two places are on the forecast for Saturday. A ‘yellow’ alert has been issued for Delhi on Saturday, which is a warning to ‘be aware’.
With overcast skies and intermittent rainfall, the maximum temperature dipped to 27.6 degrees Celsius on Friday, seven degrees below the normal for this time of the year.