Mumbai is witnessing a monsoon like never before. On May 26, the southwest monsoon arrived in the city a staggering 16 days ahead of its usual date, setting a new record for the earliest-ever onset in the financial capital. What followed was relentless rain that brought the city to a halt and shattered century-old records.
According to the India Meteorological Department (IMD), Mumbai City (Colaba observatory) received 456.5 mm of rain and the Suburbs (Santacruz observatory) 342 mm between May 1 and May 27. This makes May 2025 the wettest May ever recorded in Mumbai, breaking the previous record of 280 mm set in 1918.
The most dramatic rainfall occurred in just two days. From 8:30 am on May 25 to 8:30 am on May 26, Colaba received 135.4 mm of rain a 67,600% excess over the average of 0.2 mm. The next day, it rose to 161.9 mm an excess of over 26,800%. The suburbs saw similarly staggering spikes.
Experts believe this extreme weather is linked to multiple atmospheric and oceanic systems colliding over the region. M Rajeevan Nair, former Secretary of the Ministry of Earth Sciences, confirmed that “a low-pressure system and early monsoon convergence caused very high-intensity rainfall over short periods, which is becoming more frequent with global warming.”
Rajesh Kapadia, a Mumbai-based weather forecaster, called the event unprecedented in his five-decade career. He pointed to an unusual low-pressure system that moved inland from the Arabian Sea and created a “pull effect” that rapidly accelerated the monsoon’s northward advance. Normally, the monsoon takes 10–11 days to travel from Kerala to Mumbai. This year, it covered the stretch in just two.
K S Hosalikar, former head of Climate Research & Services at IMD Pune, cited a mix of strong south-westerly currents over the Arabian Sea, an upper air circulation near Ratnagiri, and remnants of a depression over Marathwada that intensified the westerly flow all of which funneled massive moisture into Konkan, including Mumbai.
But the most striking revelation from climate scientists is the call for better tracking of sub-daily rainfall extremes intense rain in short durations which is what Mumbai experienced. “We need more precise hourly rainfall forecasting, not just daily totals,” said Rajeevan, co-author of a recent IISER Tirupati study on sub-daily rainfall. The study finds that short-duration heavy rainfall events are rising in central and west coastal India a signal of worsening extremes in the climate system.
While city authorities may not have been fully prepared for the early deluge, scientists agree that Mumbai’s rainfall dynamics are changing fast. With more such downpours likely ahead, the need for robust early-warning systems not just for when rain will fall, but how fast and how hard has never been more urgent.