They say it was now within 1000 kilometres of the Bangladesh coast, located between west central bay and east central bay of the Bay of Bengal.
Preparations are afoot to tackle the impact of cyclone in vulnerable areas, where the weekly holidays of government officials have been cancelled.
In the past four days, the route of 'Mahasen' was uncertain.
But, on Tuesday night, Bangladesh Meteorological Department official, Shamsuddin Ahmed, said the cyclone was headed towards the Teknaf coast.
Similar prediction was also made in BBC’s weather forecast.
The cyclone will cross the south-eastern coast of Bangladesh and Myanmar, accompanied by tidal waves of up to five metres high, rain and gusts, it said.
National Aeronautics and Space Administration (NASA) of the United States said the cyclone might sweep through Chittagong with wind speeds up to 129 kilometres per hour.
Already, the storm had reportedly left seven people dead and 3000 homeless in Sri Lanka.
A boat carrying about 100 Rohingya Muslims capsized off western Burma with many feared drowned at the start of a mass evacuation from low-lying regions ahead of Cyclone Mahasen, a UN official said on Tuesday.
The boat struck rocks off Pauktaw township in Arakan State and sank late on Monday, Barbara Manzi, head of the Burma
office at the UN Office for the Coordination of Humanitarian Affairs (OCHA), told Reuters.
She said an unknown number of people were missing.
The cyclone may hit the Bangladesh coast by Thursday, said Shamsuddin Ahmed, the Deputy Director of Cyclone Warning Centre.
"Four things are clear now. Mahasen will cross coastal areas of Banlgadesh, its intensity has not increased, it is moving slowly, and it will hit anytime after Wednesday or on Thursday."
At around 6:00pm on Tuesday, another Met Office official, Mohammad Shah Alam had told bdnews24.com that 'Mahasen' might head for Odisha in India and not hit Bangladesh if it stayed on its course.
But, the storm had changed course, officials said.
The cyclone appeared stagnant for three hours since 9:00am on Tuesday. From 3:00pm to 6:00pm, it had advanced up to 12 kilometres. After 6:00pm until Wednesday morning, it had forwarded 40 kilometres.
One Met official, seeking anonymity, said though the storm was expected to landfall at Teknaf and the adjoining Arakan coast of Myanmar, it would impact the Cox's Bazar-Chittagong area.
Officials say the storm is not yet high intensity but that may change when it is within 500 kilometres of the coast.
As of Wednesday morning at 6:00am, Mahasen was located 1,010 kilometres south-west of Chittagong port, 945 kilometres south-west of Cox’s Bazar and 895 kilometres south to south-west of Mongla port.
Bangladesh Meteorological Department (BMD) forecast the storm was likely to intensify further and move in a north – north-easterly direction.
Maximum sustained wind speed was said to be about 62 kilometres per hour rising to 88 kilometres per hour in gusts within 54 kilometres of the storm centre is. Sea is likely to remain very rough near the storm centre.
Ports of Chittagong, Cox’s Bazar and Mongla have been advised to keep hoisted warning signal number four ‘4’ and all fishing boats, trawlers and marine vessels have been asked to dock at coast until further notice.
Minister for Disaster Management and Relief Abul Hasan Mahmud Ali said maximum preparations have been taken ahead of the storm in 13 districts. Holidays for government officials have been cancelled.
He was speaking after an inter-ministerial disaster management coordination committee meeting in the afternoon.
It was still uncertain at that time whether Mahasen would hit Bangladesh.
The minister urged all to remain calm and be prepared ahead of the cyclone, saying 49,365 volunteers are working to spread updates in the areas. “Currently there are 3,770 effective shelter homes."
"If needed, primary schools will be closed and be made shelter homes," Mahmud Ali said.
All districts having shorelines were supplied with additional Tk 300,000 and 100 metric tons of rice in advance to cope with post-cyclone impact. One medical team will be working in each Union along the shorelines.
Volunteers of Chittagong City Corporation, district administration and several other orgnisations were ready for 'Mahasen', local bdnews24.com office reported.
Warning announcements were being made on behalf of the administration.
Besides launching a control room, preparations have been made for evacuation, if necessary, said SM Abdul Quader, Chittagong Additional Deputy Commissioner and Convenor of a committee formed for the cyclone.
"Evacuation will take place once the danger signal rises. Force will be used if necessary."
About 100 tonnes of rice were sent to seven coastal Upazilas with Swandip receiving 20 tonnes alone, he said.
As many as 520 cyclone centres were ready with 283 medical teams. Several schools and colleges were also prepared to become shelter homes, officials said.