Mumbai rains: Why accurate weather predictions remain a challenge

On most mornings during monsoon, Mumbai wakes up to uncertainty—not just about whether to carry an umbrella, but about whether the city will grind to a halt. The India Meteorological Department (IMD), tasked with predicting rainfall patterns, has long struggled with the unique microclimate of Mumbai, where a sunny sky can turn into a deluge within minutes.

This year, however, the IMD’s red alert has come strikingly close to what the skies have delivered. For once, the prediction of “extremely heavy rainfall” matched the reality on the ground.

But historically, Mumbai’s relationship with weather forecasts has been one of frustration. Time and again, the city has either been caught off guard by a heavy downpour that went unpredicted, or forced into panic by forecasts that never materialised.

Take the catastrophic floods of July 26, 2005. On that day, Mumbai received 944 mm of rainfall in a matter of hours—an unprecedented event. IMD had issued no warning of such intensity, leaving the city paralysed and unprepared. “We had no idea something like that was coming. The forecast simply said heavy rains,” recalls Tina Sachdev, a resident of Prabhadevi. 

Red and orange alerts have sometimes caused schools to shut down and offices to declare holidays, only for the skies to remain relatively calm. " I remember there have been so many instances when the school announced closure due to red alert type forecasts issued by the Meteorological department, but that day actually remains so dry," says Shaanvi Singh, a parent of two school-going children who passed out last year.

Experts say Mumbai’s geography makes accurate forecasting a challenge. The city sits on a narrow peninsula, surrounded by the Arabian Sea, with complex wind patterns and urban heat islands influencing rainfall. “Forecasting in Mumbai is not just about predicting rainfall, it’s about predicting rainfall at hyper-local levels—something even the best models struggle with,” say independent forecast experts. Reportedly, as per RTI data, IMD's 256 warnings for heavy to severe rainfall in Mumbai were accurate only 46% of the time from 2020 to 2024. 

According to a research paper authored by Subimal Ghosh of IIT Bombay, "the Global Forecast System (GFS) model struggles to forecast extreme rainfall in Mumbai, leading to low hit rates and high false alarms." In the paper titled, 'Hyperlocal Extreme Rainfall Forecasts in Mumbai,' he says Mumbai, a coastal city, experiences multiple extreme precipitation events with significant spatial variability during the monsoon season that lasts from June to September. 

Ghosh's team launched an AI-powered app late last month and as per information shared by him, who is also head of the department and the Principal Investigator of the project at IIT's centre for climate studies,  the model works by analysing the rainbands and weather systems over the past few hours to forecast the incoming rain patterns. “The idea is to analyse the data from the past few hours about the rainbands, cloud formation, wind speed and other factors. On the basis of such data provided by the radars, the model will use machine learning to understand the existing systems and analyse them to predict the rain over the next hour. The data for the model is being procured from the IMD radars,” he said.

Add to this the rapid pace of climate change, which has made extreme rainfall events more frequent and erratic. Sudden cloudbursts, intense but short-lived, often escape radar until they are underway.

Now with AI-enabled technologies available, the department has been able to issue more precise warnings, at least for large-scale events. Authorities too have begun taking pre-emptive action—shutting down vulnerable areas, moving people out of low-lying zones, and issuing advisories in advance.

“It’s not perfect, but it’s far better than before. At least people are not caught completely off guard,”  says Charu Mehra, a professional who resides in Thane.

While today’s near-accurate red alert brings some relief, Mumbai remains wary. After all, in this city, rain is not just about the weather—it’s about survival, economy, and trust in institutions. Until IMD’s predictions consistently match reality, Mumbaikars will continue to look up at the sky with more doubt than certainty.