The heavy rainfall, driven by a low-pressure system in the Bay of Bengal and strong southeasterly winds, impacted several districts of West Bengal this week. As per India Meteorological Department (IMD) data released on May 1, Canning recorded 108 mm of rainfall within a 24-hour period, till Thursday noon. The IMD has warned that the wet spell is likely to persist until the first week of May in West Bengal due to a combination of active pre-monsoon systems.In Kolkata (Alipore), the maximum temperature reached 28.2°C, while the minimum was recorded at 19.8°C, accompanied by 31.8 mm of rainfall.The state experienced a highly active weather pattern, with the average cumulative rainfall for the state standing at 18.9 mm.Additionally, a squall was reported by the Met office Kolkata on the evening of April 30, with wind speeds reaching 55 kmph from a westerly direction.As per the weather office, Kolkata has set a new record for rainfall this April. The rain, which began after 8.30 pm on April 29 across Kolkata and South Bengal, did not remain confined to the southern districts. Moving from Nepal through Bihar and North Bengal, it resulted in several hours of continuous heavy rain across South Bengal and large parts of Odisha. The Alipore weather office reported that Kolkata recorded 54.2 mm of rainfall during this period.According to records from the Indian Institute of Tropical Meteorology (IITM) in Pune, there have been only six instances where Kolkata received more rain in a single day in April.Story continues below this adAccording to the Meteorological Department’s calculations, 9.1 mm of rain fell on Wednesday morning, followed by 62.8 mm after 8.30 pm. This continuous downpour caused Kolkata’s temperature to drop by 8 to 10 degrees Celsius. On Wednesday, the city’s maximum temperature reached 32.2 degrees.The distribution of rainfall was particularly heavy in South Bengal compared to the North. While Newlands in Alipurduar saw the highest northern rainfall at 26.8 mm, several locations in the south recorded much higher volumes, led by Jhargram with 52.4 mm and Digha with 51.9 mm.The IMD claimed that an upper air cyclonic circulation, located at around 0.9 km above sea level, is responsible for the current weather pattern over Gangetic West Bengal and neighboring Bangladesh. Alongside this, there has been a trough that stretches from southeast Uttar Pradesh to north interior Odisha to Chhattisgarh.Meteorologists explained that these systems, combined with a steady inflow of moisture from the Bay of Bengal, are fuelling cloud formation and sustained rainfall activity. The interaction between warm surface conditions and moisture-laden winds has further intensified convection, leading to repeated spells of thunderstorms, typical of the pre-monsoon ‘Kalbaishakhi’ pattern, but currently more widespread and persistent due to multi-layer atmospheric support.Story continues below this adAs a result, rainfall activity has increased across both South and North Bengal, with several districts already recording significant precipitation over the past 24 hours.In South Bengal, districts including Kolkata, Howrah, Hooghly, North and South 24 Parganas, and Nadia have witnessed light to moderate rain accompanied by thunderstorms. IMD has warned that heavy rainfall is likely at isolated places in Nadia and the 24 Parganas, along with gusty winds with speeds reaching 50-60 kmph.Rainfall data shows notable accumulations, with Amta in Howrah recording 10 cm, while Salt Lake and several locations in the 24 Parganas received around 5-6 cm. Kolkata’s Alipore observatory recorded 5 cm during the same period.Weather along the coastsCoastal and adjoining districts such as East and West Midnapore and Jhargram are also experiencing frequent thunderstorms with wind speeds ranging between 40-50 kmph. Kalaikunda recorded 8 cm of rainfall, while Digha and Contai reported 5-6 cm. The IMD has cautioned that these conditions may lead to localised disruptions, particularly in coastal areas.Story continues below this adThere have been reports of occasional rainfall and thunderstorms in the western districts of Bankura, Purulia, and the East and West Bardhaman districts. In recent days, these areas have also seen extreme weather, such as isolated hailstorms and a squall with winds as high as 62 kmph, underscoring the instability of the current weather system.The situation is more intense in North Bengal, where districts such as Jalpaiguri, Alipurduar, and Cooch Behar are emerging as the heaviest rainfall zones. The IMD has forecast heavy to very heavy rainfall of 7-20 cm in these areas over the next few days.This perspective is supported by recent observations. While some tea garden locations in Jalpaiguri and Alipurduar reported between 4-7 cm of rainfall, Maynaguri in Jalpaiguri recorded 7 cm. Concerns over waterlogging, rising river levels, and potential flooding are raised by the extensive rainfall in these locations.Risk of landslides in hilly districtsHilly districts such as Darjeeling and Kalimpong are also expected to receive widespread rainfall. Authorities have flagged the risk of landslides and reduced visibility in these areas.Story continues below this adFurther south, thunderstorms with heavy rainfall and strong winds up to 60 kmph are expected in Malda and the two districts of Dinajpur.The persistent cloud cover and rainfall have led to a noticeable drop in temperatures across the state. IMD data indicates that maximum temperatures are currently 2-3 degrees Celsius below normal in many districts. Kolkata, for instance, is expected to see daytime temperatures hovering around 30-32°C over the next few days which is lower than typical early May conditions.Residents have been advised to remain cautious, particularly during lightning activity and intense spells of rain.Alert to fishermenA specific warning has been issued for fishermen, with squally winds of 40-50 kmph, gusting up to 60 kmph, expected along and off the West Bengal coast between May 1 and May 4. According to the IMD, both North and South Bengal will experience fairly widespread to extensive rains and thunderstorms throughout the first week of May, with activity progressively decreasing but continuing into the second week.(Avantika Basu is an intern with The Indian Express)