The president cited his administration’s response to Hurricane Maria a year ago, which decimated Puerto Rico, as an “unsung success”. This despite the chorus of criticism at the time, accusing Trump of a slow and paltry responseto the devastation that ultimately is estimated to have cost almost 3,000 lives.

The almost 500-mile wide Hurricane Florence swirling towards the US east coast “could be the most dangerous storm in the history of the Carolinas”, the Federal Emergency Management Agency (Fema) administrator, Brock Long, warned on Tuesday afternoon.

Long cautioned coastal residents via Twitter of storm surges up to 12ft – “rapid rise of water that is overwhelming and deadly”.

Forecasters said the hurricane is not expected to change course in such a way that it will avoid a direct hit on the east coast late Thursday into Friday, threatening ocean surges and flooding from torrential rain inland.

Officials have called for the mandatory evacuation of more than 1.4 million coastal residents across the Carolinas and Virginia. Those states plus Maryland and Washington DC have all declared a state of emergency.

Craig Fugate, a former Fema director, said: “I’m afraid, based on my experience at Fema, that the public is probably not as prepared as everybody would like.” Many parts of the Appalachians have been saturated with rain over recent weeks, adding to concerns for flash flooding and mudslides inland.

“This one really scares me,” said the National Hurricane Center director, Ken Graham, who called the storm’s size “staggering”.

The storm was around 400 miles south of Bermuda on Tuesday afternoon and is trudging towards the east coast at 16mph. At more than 470 miles across, Florence is 56% wider than the typical Atlantic hurricane.

The eye of the storm is forecast to make landfall late on Thursday or early Friday along a coastline already saturated by rising seas, and then the system could meander over land for days. Seven-day rainfall totals are forecast to reach as much as 30in in some places.

“You’re going to get heavy rain, catastrophic, life-threatening storm surge, and also the winds,” Graham said.

Trump attempted on Tuesday to assure Americans that his government is “absolutely, totally prepared” for the storm, which he described as “tremendously big and tremendously wet”.

Ever since the federal government’s inadequate preparation and relief efforts during Hurricane Katrina in 2005, under president George W Bush, storm response has become a scrutinized measure of an administration’s efficiency.

Florence could hit the Carolinas harder than any hurricane since Hazel packed 130mph (209kph) winds in 1954 and killed 19 people in North Carolina. Since then, thousands of people have moved to the coast.

Ahead of Florence’s arrival, barrier islands were already seeing dangerous rip currents and seawater flowed over a state highway, the harbinger of a storm surge that could wipe out dunes and submerge entire communities.

“The water could overtake some of these barrier islands and keep on going. All you have to do is look up at your ceiling, and think about 12ft [of water]. That, folks, is extremely life-threatening,” said Graham.

Florence’s projected path includes half a dozen nuclear power plants, pits holding industrial waste, and numerous hog farms storing animal waste in open-air lagoons. Chinese-owned Smithfield Foods announced it will shut down the world’s largest slaughterhouse for pigs, which can kill 35,000 animals a day, in Tar Heel, North Carolina, during the storm.

Ryan Moser, a spokesman for the North Carolina-based electricity company Duke Energy, said operators would begin shutting down nuclear plants at least two hours before hurricane-force winds arrive.

A warm ocean gives hurricanes their energy, and Florence is moving over an area with water temperatures nearing 85F (30C), hurricane specialist Eric Blake reported. Hurricane-strength winds have been expanding to a range of 40 miles from the eye of the storm.Information gathered on Tuesday by a hurricane-hunting aircraft suggests it will intensify again as it nears the coast, approaching the 157mph threshold for a worst-case category 5 scenario.

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