Explained: Monsoon in May: What's Behind Weather Whiplash in Mumbai, Delhi, Bengaluru?

Heavy rain, waterlogged streets, drifting cars, and overflowing drains—this is what May looked like in many parts of India, a month typically marked by sweltering heat. What’s especially striking was the speed of the monsoon’s progression this year—it advanced from Kerala to Mumbai in just two days, a journey that normally takes about a week as the system moves gradually northward.Between 1 May and 27 May, Mumbai reported a record-breaking 456.5 mm of rainfall, making May 2025 the wettest May in Mumbai till date, according to the Indian Meteorological Department (IMD)'s rainfall data.This rapid advance follows heavy rainfall in Bengaluru last week, which triggered severe flooding, and comes on the heels of Delhi experiencing sudden, intense bursts of rain and storms through the month.The IMD has forecast that heavy rainfall will continue over Goa, Karnataka, Kerala, and the ghat areas of Tamil Nadu till 30 May. Thunderstorms are also expected to persist in northwest India for the next four to five days, including in Delhi, where an Orange Alert has been issued.What’s fueling this extreme weather, and are we bracing for more unpredictability in the coming months?The Quint explains.After Delhi, Massive Dust Storm Hits Mumbai: How Do They Impact Your Health?This year, monsoon in Southwest India has arrived sooner than expected—in Mumbai's case, 15-16 days earlier than the usual onset date of 11 June, marking the earliest recorded arrival of monsoon for the city."The current rainfall seen in Mumbai, for instance, wasn't a normal monsoon pattern", says Sahana Hegde, a Mumbai-based agro-meteorologist with nearly a decade of experience in weather advisories, climatology and future climate projections. Why did this happen? The conditions were favourable for the early onset of monsoon this year due to a range of overlapping factors, according to experts.Mumbai's Monsoon 'Mayhem': The Annual Disaster We're Told to Accept"The depression created in atmospheric pressure in the Arabian Sea is a major contributing factor, which is why the western coast is particularly affected this time."Sahana HegdeDepressions in atmospheric pressure are low-pressure areas in the atmosphere where warm, moist air rises rapidly. As the air rises, it cools and condenses to form clouds. This process can lead to heavy rainfall and, in some cases, develop into cyclones if the conditions are favourable.Hegde explains,"One reason could be the monsoonal wind patterns, and another might be the temperature differences between land and ocean, as well as between different oceans. Together, these factors may have created favourable conditions for an early onset of the monsoon this year."This low pressure system was also responsible for 'pulling' the monsoon so rapidly up the coast from Kerala, travelling through the southwest coast to Maharashtra, says Soumya Datta, Climate Scientist and Co-Convener of South Asian People’s Action on Climate Crisis.Heavy Rains, Gushing Mountain Streams, 270 Dead: How Landslides Ravaged WayanadThe above reasons are related to meteorological conditions, but there are also non-weather-related contributing factors for this year's erratic rains, not least of which is global warming or climate change, according to experts."We have to remember that everything is happening in a warmer world now," senior Earth System Scientist Raghu Murtugudde tells The Quint."Also, this (the heavy rains) is coming at the tail of the last two years that were particularly warm, breaking all kinds of records," he says."It may not be a direct, tangible impact but you can see the consequence of this in everything around us. We are seeing warmer oceans, warmer atmosphere, more humidity."These three factors in particular have a direct impact on the weather, especially the rain cycle.Speaking to The Quint, Soumya Datta, explains this further."The oceans have been getting extremely warm in the last two years, so you now have this huge stretch of warm ocean and sea (Indian Ocean and Arabian Sea) in the southern part of the subcontinent, causing a lot of moisture to be pumped into the atmosphere, so the monsoon has more rainfall potential," he says.Simply put, "the hotter it gets, the lower the pressure, and that can pull the monsoon in more strongly," he concludes."Think of a sponge. If you soak it with as much water as it can hold and you squeeze the sponge (to represent atmospheric instability), all that water will not drizzle, but pour out all at once. That's how extreme rainfall also works."Raghu Murtugudde, Earth System ScientistAccording to Hegde, another contributing factor here could be air pollution."When the air contains more pollutants, the aerosols can hold more water vapour, which can lead to a sudden heavy downpour in a short period."Sahana HegdeThis is what is happening in India's southwestern coast. But, explaining the recent unseasonal, sporadic thunderstorms in parts of North India, Datta points to a similar combination of strong northerly winds and extreme heat in the northwest as the primary cause. "Apart from the oceans, even when there's significant heat buildup in land, like in the northern part of the Indian subcontinent," he explains, "the resulting low pressure pulls in the monsoon winds more quickly, as we have seen happen in Delhi this time."In Photos: Alarming Pictures Chronicle Extreme Floods In New Delhi When low-pressure systems like this form in the atmosphere, they typically bring short-lived bursts of intense rain. This type of rainfall comes in waves with periods of heavy downpour followed by dry spells, say experts."With warming, we are going to get extreme thunderstorms like this, but we are also going to get droughts in many places," says Murtugudde.According to the IMD, the current spell of rain in parts of Tamil Nadu and the Konkan coast isn't expected to last long, likely tapering off by the end of the week. Experts say that when there's intense rain early in the season or just before the official onset of the monsoon, it can sometimes be followed by a weaker or drier monsoon overall.In fact, a 2017 review of long-term rainfall trends in India, published by the IMD, revealed that approximately 10 percent of districts experienced a significant decrease in annual rainfall between 1901-2013.A more recent report published in Journal of Water and Climate Change by researchers at IIT indore in 2023 also found a decrease in annual, monsoon, post-monsoon, and winter rainfall, but an increase in rainfall during the pre-monsoon season.This suggests a trend toward more intense but less frequent rainfall events—a pattern consistent with the broader impacts of climate change.'A Year of Failed Crops': Erratic Rain, Overflowing Lakes Hurt Haryana FarmersThis may not be the established pattern yet, but experts The Quint spoke to say climate change will increase climatic variability in the future. This means we can expect more sudden, intense rains occurring in short bursts, separated by longer and more sporadic dry intervals.Which also means we should start preparing accordingly."The main challenge here is that these are all global drivers and what happens here is not local, and so we don't have much control over them. What we do have control over is our own infrastructure—building proper drainage, ensuring enough green cover in cities, etc," says Murtugudde.Datta agrees, adding, "The urban flooding doesn't just happen because of heavy rainfall. It happens because the drainage capacity of the cities can't keep up with the rainfall."In addition to poor drainage systems, he points out that the rapid urbanisation of cities in India have led to construction on low-lying areas, lakes, and riverbanks. This has severely limited the natural pathways for water to flow out of the city or seep into the ground."In Delhi, places like the Akshardham Temple and the Commonwealth Village have been built on land that was once part of the Yamuna riverbed. The riverbanks have also been artificially narrowed using constructed walls. During heavy rainfall, these walls can't contain the water, causing it to overflow into the surrounding low-lying areas."Soumya DattaThis is true for most of our cities. "The way our cities are built, there is no way for the water to escape efficiently during heavy rains," says Hegde. "Within the cities, a lot of existing low-lying areas, wetlands, and lakes, areas where water would collect and percolate into the ground have been built on. So there is no space for the rainwater to escape.""Our cities have completely messed up drainage. Otherwise there is no reason for cities like Mumbai and Chennai, which sit by the sea, should be flooded," adds Datta.The bottom line is, our cities are not designed to handle large volumes of rainfall all at once, and the destruction and urban flooding we're witnessing are consequences of climate change-driven erraticnweather combined with poor urban planning and maldevelopment.

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Summer Turns Stormy: What's Behind Weather Whiplash in Mumbai, Delhi, Bengaluru?

This year’s monsoon arrived 15-16 days earlier than usual in Mumbai, marking a new record for the city.