A depression in the Bay of Bengal, compounded by an active cyclonic circulation, is set to bring heavy to very heavy rainfall across south Bengal and parts of north Bengal from 12 August through 15 August 2025, the India Meteorological Department (IMD) warned on Wednesday. The weather system has already triggered deadly lightning strikes in Purulia district, killing four people on Tuesday evening.

The Weather System Driving the Rains

According to the IMD, a cyclonic circulation has developed over the northwest Bay of Bengal and adjoining areas, extending vertically up to approximately 7.6 km above sea level. The department indicated that a depression was likely to consolidate from this system on Wednesday itself, intensifying rainfall activity across both south and north Bengal over the coming days.

This comes amid a period when the Bay of Bengal typically remains active during the monsoon peak, and back-to-back weather systems have repeatedly disrupted normal life across coastal West Bengal in recent weeks.

District-wise Rainfall Forecast

On Wednesday (12 August), light to moderate rain is expected across virtually all districts of south Bengal. Heavy to very heavy rainfall is forecast specifically for North 24 Parganas, South 24 Parganas, East Midnapore, and West Midnapore. Kolkata, Howrah, Hooghly, and Bankura are also under a heavy rain warning, with thunderstorms and gusty winds of 30 to 40 kilometres per hour likely.

On Thursday (13 August), heavy rain is expected in East Midnapore, West Midnapore, South 24 Parganas, Jhargram, Bankura, Purulia, and West Burdwan. By Friday (14 August), the rain belt shifts toward East Burdwan, West Burdwan, Purulia, and Birbhum. On Independence Day, 15 August, Birbhum, East Burdwan, and Nadia remain under a heavy rain forecast.

In north Bengal, Jalpaiguri and Alipurduar face heavy rain on Thursday. By 14 August, five districts — Darjeeling, Kalimpong, Jalpaiguri, Alipurduar, and Cooch Behar — are under warning. A heavy rain alert remains in place for Darjeeling, Jalpaiguri, and Cooch Behar on 15 August.

Lightning Kills Four in Purulia

The deteriorating weather has already claimed lives. Four people died and at least eight were injured after lightning struck multiple locations in Purulia district on Tuesday evening.

In the Joypur police station area, lightning struck a group of female agricultural workers planting paddy seedlings in a field. Sunita Gope (50) was declared dead at the Joypur Block Health Centre; four women from the group were injured and taken to the same facility.

Separately, Gaur Garai (70), a resident of Rangadi village under Balrampur police station, died after lightning struck him while he was grazing cattle in a field. In Lachmanpur village under Arsha police station, Bharati Mahato (51) was fatally struck while returning home after grazing goats. A fourth fatality, Sachinath Mahato (45), died after being struck by lightning while working in a field in Kanchanpur village under the same police station jurisdiction.

Kolkata Temperature and Conditions

On Tuesday, Kolkata recorded a maximum temperature of 32.06 degrees Celsius — marginally 0.02 degrees above normal — while the minimum temperature stood at 25.07 degrees Celsius, which is 1.01 degrees below normal. The combination of high humidity and approaching rain bands is expected to keep conditions oppressive through the week.

Authorities have urged residents in low-lying coastal districts and agricultural workers across the affected zones to exercise extreme caution, particularly given the elevated lightning risk that typically accompanies such Bay of Bengal weather systems.