Island city logs wettest May in over a century

Time of India

27-05-2025

Mumbai: The southwest monsoon made a historic early arrival over Mumbai on Monday — the earliest onset ever recorded for the city. The previous record was May 29, recorded in 1956, 1962, and 1971 (records date back to 1950).
Early onset coincided with the island city of Mumbai breaking a 100-year-old record for rainfall received in May, which has now touched 295mm.
The onset over Mumbai comes barely two days after the monsoon was declared over Kerala (May 24), and a day after its advance into parts of Maharashtra, up to Devgad (May 25) in Ratnagiri. Shubhangi Bhute, head of IMD Mumbai, said, "Typically, the monsoon sets in around June 11, so this year's onset is significantly early…a red alert has been issued for Mumbai, Thane, and Raigad.
For tomorrow, however, Mumbai will be under a yellow alert.
"
The
India Meteorological Department
(IMD), which had initially issued a yellow alert for Monday—indicating possibility of thunderstorms, lightning, and heavy rain at isolated places—upgraded the alert to orange on Monday morning in response to the persistent downpour. This signalled the likelihood of heavy to very heavy rain at isolated locations. By Monday afternoon, as the rainfall showed no signs of abating and waterlogging began affecting several parts of the city, the alert was further escalated to red, warning of extremely heavy rain in isolated areas.
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The IMD Colaba observatory which broke the all-time rainfall record for May, logging 439 mm so far, surpassed the previous record of 279.4 mm set in May 1918. Even during Cyclone Tauktae in May 2021, the station had recorded slightly less rain at 257.8 mm. The Santacruz observatory, which covers the suburbs, has so far recorded 272 mm of rain this month. The record for the highest rainall in May at Santacruz stands at 387mm in the year 2000.
During Monday's intense rain spell, south Mumbai was hit hardest in the first wave of showers. According to the IMD, average rainfall recorded between 8:30 am and 5:30 pm was 144.3 mm at Colaba—classified as "very heavy rain" (115.6–204.4 mm)—and 74.3 mm at Santacruz, falling under the "heavy rain" category (64.5–115.5 mm). However, more granular data from the BMC's automatic weather stations (AWS) revealed that Nariman Point alone received 104 mm of rain in just one hour on Monday morning.
Other heavily affected spots included the A Ward Office (86 mm), Municipal Head Office at Fort (80 mm), Grant Road Eye Hospital (67 mm), Malabar Hill (63 mm), and D Ward, Nana Chowk (61 mm).
The IMD, however, did not call this a cloudburst; it said it was an 'intense rain spell'. A cloudburst is typically defined as extremely intense rainfall—usually 100 mm or more in one hour—over a small area, which often leads to flash floods, landslides, and severe water logging.
The IMD said that none of its observatory data showed any location recording such intensity rainfall within a one-hour period, and therefore, the cloud burst criteria were not met.
Meanwhile triple digit rainfall was also recorded in south Mumbai between May 25-26 as the IMD's Colaba observatory recorded 135.4 mm of rainfall in the 24 hours ending 8:30 am Monday, categorised as "very heavy rain". In contrast, the Santacruz observatory recorded 33.5 mm.
Weather enthusiast Athreya Shetty explained that the intense rainfall over south Mumbai was due to the remnants of a depression from the Arabian Sea, which had stalled near Pune over the weekend. "There was strong convergence on the western flank of this system, spanning from Mumbai to Ratnagiri," he said. "As a result, a high concentration of moisture built up over the south Mumbai–Raigad–Navi Mumbai–Karjat belt, forcing the air to rise rapidly and form towering cumulonimbus thunderstorms—some reaching up to 15 km in height.
These systems brought intense rain and thunderstorms from the east."
Shetty said because most of the storm activity was concentrated in this belt and winds were easterly, the northern suburbs were largely spared, leading to intense rains being limited to southern parts of the Mumbai Metropolitan Region.