The India Meteorological Department (IMD) on Monday forecast heavy to very heavy rainfall in parts of south Bengal from July 23 to 27, owing to the likely formation of a low-pressure area over north Bay of Bengal around July 24.

In its bulletin, the IMD said, “The monsoon trough at mean sea level now passes through Jammu, Chandigarh, Sarsawa, Fatehgarh, Varanasi, Ranchi, Digha and thence east-southeastwards to northeast Bay of Bengal. The upper air cyclonic circulation over west central and adjoining northwest Bay of Bengal off south Odisha–north Coastal Andhra Pradesh now lies over south Odisha and neighbourhood and extends up to 5.8 km above mean sea level, tilting southeastwards with height. A low-pressure area is likely to form over North Bay of Bengal around 24th July, 2025.”

Due to the anticipated low-pressure area, rainfall activity is likely to increase with isolated heavy to very heavy rain expected over districts of South Bengal from July 23 to 27.

According to the IMD, “Light to moderate rain/thundershower likely to occur at a few places over districts of South Bengal with gusty wind speed reaching 30 to 40 kmph and lightning very likely to occur at one or two places over North & South 24 Parganas, Howrah, East & West Midnapore, Jhargram, Purulia, West Burdwan, Birbhum and Bankura districts” on July 21 and July 22.

From July 23 onwards, rainfall intensity is expected to rise. “Heavy to very rainfall (07-20 cm) very likely to occur at one or two places over South 24 Parganas, East & West Midnapore, Bankura, Purulia and Hooghly districts and heavy rainfall (07-11 cm) very likely to occur at one or two places over rest districts of South Bengal,” the bulletin said.

The possible impacts in South Bengal during July 23-27 include waterlogging in low-lying areas, traffic disruption, damage to vulnerable structures, rise in river water levels, risk of lightning strikes in open fields, and potential harm to crops and vegetables.

Advisories issued include avoiding waterlogged areas, taking shelter during heavy rain or thunderstorms, and avoiding shelter under trees or electric poles.

For north Bengal, the IMD predicted “light to moderate rain/thundershower at many places” over most districts till July 27. Heavy rainfall is likely at isolated places in Darjeeling, Kalimpong, Jalpaiguri, Alipurduar and Coochbehar between July 25 and July 27.

The IMD also warned fishermen of squally weather over north and central Bay of Bengal, along and off West Bengal–Odisha coast from July 24. “Squally weather with surface wind speed reaching 35 to 45 kmph gusting to 55 kmph very likely to prevail. Fishermen are advised not to venture into the sea from 24/07/2025 till further notice,” it said.

In the last 24 hours till 8.30 am on Monday, Balurghat recorded the highest rainfall in the state at 45 mm, the IMD added.