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What caused Delhi downpour & rainy Tuesday — monsoon revival & other systems piled up at once
The season's first Bay of Bengal depression, a low-pressure area over Rajasthan and a western disturbance are all tugging at the monsoon trough at once.
Rain battered Delhi-NCR on Tuesday, sending waist-deep waters into markets, submerging key stretches and grinding traffic to a halt, and prompting the Met department to escalate its warning through the morning — yellow, then orange, and finally red at 12.25pm, its highest tier.
ITO, Nizamuddin, South Extension and the Delhi-Meerut Expressway were among the affected areas, and very heavy rain was reported across Noida, Ghaziabad and Gurgaon.
Behind it all is not one weather system, but four.
Why the rain came back
The southwest monsoon had a sluggish start. National rainfall deficit stood at close to 40% at the end of June, but rain in early July narrowed the gap to 16%, though the deficit remains wider in some pockets.
Delhi's July rainfall had been trailing normal until this week too — Safdarjung had recorded 160.3mm against a monthly normal of 195.8mm before Tuesday, and only 27.5mm of that fell in the past 15 days, private forecaster Skymet Weather noted.
What broke the lull is a monsoon revival layered with other systems.
The monsoon trough — the rain-bearing spine of the monsoon — now runs south of Delhi through Bikaner, Gwalior, Satna and Daltonganj eastward to the centre of a deep depression that made landfall over the West Bengal-north Odisha coasts in the early hours of Tuesday, the India Meteorological Department (IMD) said in its bulletin.
It is the season’s first Bay of Bengal depression to move inland, independent meteorologist Navdeep Dahiya noted on X.
Two upper-air cyclonic circulations complete the picture, according to the IMD bulletin. One of them is over southwest Rajasthan, sitting at the monsoon trough’s western end, and another over northern parts of central Uttar Pradesh, closer to Delhi-NCR.
Also read: What an El Niño year means for India’s monsoon
What a monsoon trough is
Through the monsoon months, an elongated belt of low pressure — called the monsoon trough — normally stretches from a heat-driven low over Pakistan to the head of the Bay of Bengal, roughly tracking the Gangetic plain.
The trough is not fixed. Its eastern end can drift five degrees of latitude within a single day.
Where this trough settles decides which area gets rain. Pulled south of its usual line, it drags the belt of heaviest rain over central and northern India — broadly, where Delhi-NCR now sits. But pushed north toward the Himalayan foothills, the plains dry out in what forecasters call a "break" in the monsoon.
Amplifying features at either end raise the intensity. The Rajasthan circulation and the Odisha deep depression each force moisture upward on their own. Anchored to the trough, they turn a merely favourable position into a productive one.
Warm, moist air converging into these systems is forced upward, rising air cools, and the water it carries condenses into cloud droplets, eventually dropping as rain.
Also read: Kharif crops: You reap what you sow — unless the monsoon has other plans
What it means for farmers & the rest of rainy season
Monsoon's revival was already visible in the fields. Summer crop sowing was nearly a quarter short of last year's pace at the end of June, but that shortfall has narrowed to under 5%, according to data by the Union Ministry of Agriculture and Farmers' Welfare cited by Reuters.
Farmers had planted 78.7 million hectares as of July 24, against 82.6 million a year earlier, with rice — which farmers time to the arrival of the rains — on 23.4 million hectares, only marginally behind last year's pace.
"We were waiting for rain before transplanting the seedlings. After we received good rainfall this month, we started paddy transplanting," Krishna Beuraa, a farmer in Konark in Odisha, told Reuters.
For Delhi-NCR, the IMD has forecast heavy to very heavy rain at isolated places on July 28 and 29, followed by fairly widespread rain through August 3.
Whether the momentum holds through the rest of the season is a separate question. Skymet noted in a post on X that the August and September picture will be shaped by two large climate signals: El Niño, the Pacific warming pattern that has historically weakened Indian monsoons, and the Indian Ocean Dipole, a temperature see-saw between the eastern and western Indian Ocean that can either boost or blunt subcontinental rainfall.
For the moment, the trough is fluttering close to Delhi-NCR.
