Written by Arghya ChakravortyA low-pressure area is likely to form over the coastal areas of Gangetic West Bengal and the adjacent northwest Bay of Bengal during the next 24 hours, with the India Meteorological Department (IMD) forecasting heavy to very heavy rainfall over parts of south Bengal and extensive thunderstorms across the state in the coming days. According to the Met, an upper-air cyclonic circulation persists over south Gangetic West Bengal and neighbouring Bangladesh, reaching up to about 7.6 km above mean sea level and leaning southwards, resulting in the likely formation of a low-pressure area during the next 24 hours. The IMD said that the prevailing synoptic conditions are likely to enhance rainfall activity. For south Bengal, IMD warned of heavy to very heavy rainfall (7-20 cm) at one or two places over Purba and Paschim Medinipur and South 24 Parganas districts on Thursday, while heavy rainfall (7-11 cm) is likely over Jhargram, North 24 Parganas, Kolkata, Howrah, Hooghly and Bankura. Thunderstorms accompanied by lightning and gusty surface winds reaching up to 30-40 kmph are also expected.