Meteorologists have stated that the forecasting models did not anticipate the extreme weather event that caught Delhi residents off guard early Friday, resulting in a historic 228.1 mm of rainfall.
This quantity exceeds the June average of 74.1 mm by more than three times and marks the highest for the month since 1936.
An official from the IMD clarified that the monsoon winds interacted with the remnants of a western disturbance, leading to heavy rains in Delhi, Himachal Pradesh, and Jammu and Kashmir.
Independent scientists say a thunderstorm over North Delhi could have sparked the torrential rains.
On June 26, the IMD had forecasted only light to moderate rain and thunderstorms with gusty winds for Friday (June 28).
On Thursday afternoon, the Met office noted a trough extending from a cyclonic circulation over central Gujarat to west Bihar in the lower tropospheric levels.
In the weekly weather briefing uploaded on the IMD's YouTube page, scientist Soma Sen Roy said this trough was pumping moisture into north and central India.
"The east-west trough is likely to strengthen during the week, and rainfall will increase over north India," she explained.
The extended range forecast released by the IMD on Thursday night anticipated "a fairly widespread to widespread occurrence of light to moderate rainfall accompanied by thunderstorms and lightning across northwest and east India over the next five days".
The forecast also indicated the possibility of "extremely heavy rainfall" in Delhi on June 29 and June 30, although no one foresaw the heavy rain on Friday morning.
At 4:58 am on Friday, the IMD issued an alert, stating "light to moderate intensity rain with heavy intensity rain over a few places and winds of 20-40 kmph would occur over and adjoining areas of entire Delhi and NCR, Gannaur, Sonepat, Kharkhoda, Jhajjar, Sohna, Palwal, Baraut, Baghpat, Khekra, Pilakhua, and Sikandrabad during the next two hours".
Later, it reported that the Safdarjung Observatory recorded 148.5 mm of rainfall between 2:30 am and 5:30 am, indicating that much of the rain had already occurred before the IMD issued the alert.
Also, it declared the arrival of the monsoon in Delhi on Friday noon, less than 15 hours after it had projected that the primary rain-bearing system would reach Delhi within two to three days.
"Not much rainfall was happening due to the eastern arm of the monsoon in West Bengal, Bihar, and up to Uttar Pradesh. The eastern arm monsoon moved slowly. But one pulse suddenly arrived from the Madhya Pradesh side. Nobody expected this massive amount of moisture," an IMD official said, requesting anonymity.
"The models could not capture it. Also, convective clouds started developing in the evening and intensified over time. Predicting thunderstorms in advance is not easy," the official added.
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