People in parts of Florida could face an “unsurvivable” storm surge when Hurricane Helene makes landfall on Thursday.
High winds, possibly in excess of 130mph (209kph), rains and flash floods are possible across areas of the southeastern US, the US National Weather Service in Tallahassee has said.
Helene is expected to be a major hurricane – a Category 3 or higher – when it hits Florida’s northwestern coast on Thursday evening.
At lunchtime, UK time, on Thursday, the US National Hurricane Centre placed Helene around 365 miles (585km) south of Apalachicola, in the Big Bend area, and was crossing the Gulf of Mexico at sustained wind speeds of up to 100mph (155kph).
It had already intensified into a Category 2 hurricane, the centre said, and is expected to grow stronger before it hits Florida.
States of emergency have been declared in Florida, Georgia, and the Carolinas, with hurricane and flash flood warnings in place as far away as south-central Georgia.
Several Florida counties are under mandatory evacuation orders, and millions of people are under flood watches.
Storm surges of up to 20 feet (6m) are possible, the weather service said, adding they could be particularly “catastrophic and life-threatening” in Florida’s Apalachee Bay, on the state’s Big Bend coastline, south of Tallahassee.
There is also a risk of high winds and heavy rains, the office said, calling the forecast “a nightmare surge scenario” for the bay and urging residents to “please, please, please take any evacuation orders seriously!”
Tallahassee residents have been preparing to leave their homes and spent some of Wednesday stocking up on sandbags, food and supplies, NBC, Sky’s US partner, said.
The city’s mayor John Dailey urged people to take the warnings “extremely seriously”, calling Helene “the biggest storm in the history of the city to hit us head-on”.
Speaking to NBC on Wednesday, he said that though they are “very prepared”, he was also “very nervous, and I hope everyone is nervous”. He added: “This is a big storm. It is going to cause a lot of damage.”
Christine Nazworth, from Crawfordville, about 25 miles (40km) northwest of Apalachee Bay, said her family would be sheltering in place, despite Wakulla County issuing a mandatory evacuation order.
She said: “I’m prayed up. Lord have mercy on us. And everybody else that might be in its path.”
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Leslie Powell, from Quincy, a city a similar distance from Tallahassee, told NBC she was leaving her mobile home to go to a shelter with her 8-month-old baby and six-year-old daughter.
She said simply: “I’m scared. I’ve got a lot of trees around my home, so it’s not safe for me and my kids.”