The Meteorological Department has asked local authorities and two ports to raise their highest alert, as the cyclone is set to unleash a storm surge as high as two metres (seven feet) in coastal districts on Saturday evening.
Packing a maximum wind speed of 120km/h (75m/h), Bulbul is on course to make landfall in the southwestern Khulna region, near the Sundarbans, the world’s largest mangrove forest, which straddles Bangladesh and part of eastern India and is home to the endangered Bengal tigers.
The cyclone is expected to hit the Bangladesh coast at about 8pm (14:00 GMT), Shah Kamal, the country’s disaster management secretary, told AFP news agency, adding there were plans to evacuate about 1.5 million people before that.
About 55,000 volunteers have been mobilised to go door-to-door and alert people about the storm.
Authorities have suspended a nationwide school test, cancelled the holidays of officials posted in coastal districts and called off a traditional fair that draws tens of thousands of people in the Sundarbans.
Operations at the country’s two major ports – Mongla and Chittagong – have been suspended, Kamal said.
Bangladesh’s low-lying coast, home to 30 million people, is regularly battered by powerful cyclones that leave a trail of devastation in their wake.
Hundreds of thousands of people have been killed over the last few decades in cyclones, whose frequency and intensity have increased.
Bangladesh has, however, improved its preparedness in recent years, cutting the number of casualties since Cyclone Sidr killed more than 3,000 people in 2007.
In May this year, Fani became the most powerful storm to hit the country in five years, but just over a dozen people were killed.