Explained: Why Mumbai's monsoon is refusing to leave and will October stay rainy too?

Why is Mumbai still getting rain in October?

According to the IMD scientists, the continued rain activity over the city is due to an approaching western disturbance, a weather system that typically brings rain to north India during winter.

These disturbances form near the Mediterranean region, travel eastward across Afghanistan and Iran, and collect moisture from the Mediterranean, Black, Caspian, and Arabian seas. When they reach India, they often trigger unseasonal rainfall.

In Mumbai, this system has led to the formation of a monsoon trough, meaning a long, low-pressure zone stretching from Pakistan to the Bay of Bengal. When this trough dips southward, it intensifies rainfall over the western coast, including Mumbai.

As per the IMD charts, a trough is currently extending from south interior Karnataka to the Comorin region through interior Tamil Nadu, strengthening the southwest monsoon flow over the central Arabian Sea.

“While the city is experiencing warm and sunny days at present, by October 6 and 7, it may get cloudy and start experiencing enhanced rainfall. This is because a western disturbance will be affecting the region over the next couple of days. This western disturbance is presently dipping, and it will bring in moisture. This moisture availability will lead to enhanced showers, even as the intensity is likely to remain moderate,” a senior scientist from IMD Mumbai was quoted by The Indian Express as saying.

Meanwhile, officials have clarified that Cyclone Shakthi, which is active over the Arabian Sea, does not pose a threat to Maharashtra’s coast. The severe cyclonic storm is expected to move towards the northwest and adjoining west-central Arabian Sea after October 5, before changing course and weakening by October 6.

Why does Mumbai’s monsoon withdrawal often get delayed?

The IMD officially declares the withdrawal of the monsoon from Mumbai only after observing specific conditions, persistent dry weather for five consecutive days, a change in wind direction, reduced moisture in the air, and a visible shift in weather patterns.

While this year’s delay might seem unusual, scientists point out that such late withdrawals have become common for the city. In fact, Mumbai has seen delayed monsoon retreats for six consecutive years.

In 2024, the monsoon officially withdrew on October 15. In 2023 and 2022, it retreated as late as October 23. In 2021, it ended on October 14, and in 2020, the withdrawal was as late as October 28. Even in 2019, it lingered until mid-October. Experts say this pattern suggests a broader climatic shift and the increasing persistence of low-pressure systems that keep drawing moisture into the region.

Mumbai’s rainfall this year

Since the start of the monsoon in June, Mumbai has recorded significantly higher-than-average rainfall. The Santacruz observatory has logged more than 3,100 mm of rain so far, compared to the city’s seasonal average of 2,319 mm.

This year, the city received 512 mm of rain in June, 798 mm of rain in July, 1,184 mm of rain in August and 606 mm of rain in September. The Santacruz station has received 31 mm of rain in October so far, while Colaba station has logged 59 mm of rainfall.