For a week Dhaka and almost every division of Bangladesh have had continuous rain and lightning. The weather has been cool, but lightning has killed about 56 people across the country so far this season despite advance warnings. On Tuesday the Bangladesh Meteorological Department (BMD) issued a 48-hour kalbaishakhi alert from 11am: storms with winds of 60 to 80 kilometres an hour from the west or north-west, with lightning, may sweep Rangpur, Rajshahi, Mymensingh, Dhaka, Khulna, Barishal, Chattogram and Sylhet divisions.

This April has been unusually gentle. Meteorologist Muhammad Abul Kalam Mallik said the month's average temperature is normally 33.2 degrees Celsius and often swings between 36 and 42, but this year 40 degrees was reached only once, at Rajshahi on 22 April. In 2024 the country endured a 35-day heatwave, the longest in 76 years; this year there has been none, because thunderstorms have been so frequent. "The cruellest month, April, has been quite tolerable this time," he said.

March, April and May make up the pre-monsoon season. Some 38 percent of the year's thunderstorms in Bangladesh and West Bengal fall in these months and are known locally as kalbaishakhi; the roughly 51 percent that occur from June to September are simply thunderstorms. On average March brings five or six kalbaishakhi, April nine and May 13. This April had already produced more than ten, with Sylhet hit hardest. Mr Mallik attributes the surge to a disruption in the interaction between local and global atmospheric conditions, and warned that thunder-cloud formation could increase over Rajshahi and Khulna divisions from Wednesday.

The BMD also issued a 96-hour heavy-rain warning on Tuesday morning: heavy falls of 44 to 88 millimetres in 24 hours and very heavy falls of 88 millimetres or more are possible in parts of all eight divisions, with temporary waterlogging and a risk of landslides in the hill areas of Chattogram division. Fishing boats and trawlers in the north Bay of Bengal have been told to stay close to the coast and move with caution until further notice, and the ports of Chattogram, Cox's Bazar, Mongla and Payra have been told to hoist local cautionary signal number three.

The five-day forecast to 2 May calls for moderate to very heavy rain in parts of Dhaka, Mymensingh, Chattogram, Sylhet and Barishal divisions and thundershowers with gusty winds across the country. After that the rain should ease and temperatures rise. Mr Mallik expects above-normal temperatures after the first week of May and through June, with spells of intense discomfort whenever humidity is high and wind is light.

May is cyclone season. Mr Mallik expects one or two low-pressure areas to form in the Bay this month, one of which could deepen into a depression, a deep depression or a cyclone, although nothing is expected in the next ten days. There is still no scientific way to say in advance where and for how long a kalbaishakhi will strike, because the storms build within a few hours.

The outlook lands in the middle of the boro harvest. Squalls and very heavy rain threaten ripe paddy in the field and grain on the threshing floor, and pre-monsoon lightning remains the deadliest hazard for the farm labourers who bring the crop in.

Source: BBC Bangla