Kolkata: West Bengal is set to witness widespread rainfall over the next seven days, with the India Meteorological Department (IMD) forecasting scattered to moderate showers across almost all districts due to a strong influx of moisture from the Bay of Bengal.

Several districts in South Bengal are likely to receive heavy rainfall, while the hilly and adjoining districts of North Bengal remain under the threat of heavy to very heavy rain.

According to the IMD, thunderstorms accompanied by lightning and gusty winds of 30 to 40 kmph are also likely over the coming days.

In South Bengal, districts including Kolkata, Howrah, Hooghly, North and South 24 Parganas, East and West Midnapore, East and West Bardhaman, Nadia, Murshidabad, Birbhum, Bankura, Purulia and Jhargram are expected to remain under predominantly cloudy skies over the next week.

The weather office has predicted one or more spells of rain or thundershowers during the day, with heavy rainfall warnings issued for several districts on July 22 and 23.

Meteorologists said weather conditions have become increasingly favourable for widespread rainfall due to the presence of multiple active weather systems over eastern India.

The Monsoon Trough currently extends from Bikaner through Barkui, Vidisha, Pendra Road in Chhattisgarh and Jharsuguda to the northeast Bay of Bengal. In addition, a cyclonic circulation persists over the north Bay of Bengal, extending up to about 3.1 km above mean sea level.

An active East-West Shear Zone along around 11 degrees North latitude is also influencing the weather. The system is positioned between 5.8 km and 7.6 km above mean sea level and is tilted south-westward with height.

The combined impact of these systems is expected to trigger thunderstorms, lightning, gusty winds of 30 to 40 kmph and isolated heavy rainfall of 7 to 11 cm across most districts of South Bengal over the next three days.

While more districts in North Bengal are under a yellow alert on the first day, weather conditions are expected to improve slightly during the second and third days.

However, South Bengal is likely to continue experiencing favourable conditions for rain throughout the forecast period.

The IMD has advised residents, particularly in districts likely to receive heavy rainfall, to remain alert for waterlogging, reduced visibility, lightning and strong winds during thunderstorms.