"In case of late withdrawal of the monsoon, the moist air mass persists for longer durations, goes far beyond its reach and rains over parts of Rajasthan, Delhi and Haryana," he said.
The monsoon has dumped 383.4 mm of rainfall in Delhi this month till Saturday evening, the highest in September in 77 years, according to the India Meteorological Department (IMD).
The city gauged 417.3 mm of rainfall in September 1944, the highest in the 1901-2021 period. It has already received 383.4 mm of precipitation this September, till 5:30 pm on Saturday, an IMD official said.
Delhi had recorded 360.9 mm rainfall in 1914, 359.2 mm in 1945 and 341.9 mm in 1933, according to the IMD.
Delhi has also witnessed three heavy rain events this September — 112.1 mm on September 1; 117.7 mm on September 2 and 94.7 mm September 11 (Saturday) — the highest in the month in a decade.
It had recorded two heavy rain spells in September 2017.
G P Sharma, President (Meteorology), Skymet Weather, a private forecasting agency, cited two reasons for record-breaking rains this September in Delhi — “a likely late withdrawal of the monsoon and formation of low pressure systems in quick succession”.
“In case of late withdrawal of the monsoon, the moist air mass persists for longer durations, goes far beyond its reach and rains over parts of Rajasthan, Delhi and Haryana,” he said.
“Secondly, low pressure systems are forming in quick succession. We are not even halfway through the month and we have already had two good systems. In August, we had only one such system,” he said.
Delhi is headed for a new all-time rain record for September.
“Light to moderate rain is likely in the next two days. Another wet spell is predicted around September 17-18,” the official told PTI.
The September rainfall this year has been in marked contrast to last year, when the city got a meagre 20.9 mm precipitation in the month against the normal of 129.8 mm.
Despite the monsoon embracing Delhi only on July 13, making it the most-delayed in 19 years, the capital had recorded 16 rainy days in the month, the maximum in the last four years.
The string of rainy days gave 507.1 mm rainfall in Delhi, which was nearly 141 percent above the long-period average of 210.6 mm. It was also the maximum rainfall in the month since July 2003, and the second highest ever.
The city recorded just 10 rainy days in August, the lowest in seven years, and a cumulative rainfall of 214.5 mm, lower than the average of 247 mm.