The NHC warned that the storm would bring "potentially life-threatening storm surges, catastrophic winds and flooding" across the United States. Parts of Florida, Georgia and the coast of South Carolina are affected.
Florida's governor Ron DeSantis had already declared a state of emergency for all 67 counties because of "Ian" as a precaution and asked the population to create emergency supplies. "You have to evacuate now," he said, addressing people in what is likely to be the hardest hit areas. Cities on the southwest coast of the state in particular were preparing for storm surges and strong winds.
US President Joe Biden also warned people in advance of a "very violent hurricane" with "life-threatening and devastating effects". As a precautionary measure, he approved emergency aid via the US civil protection agency Fema.
The evacuation of people in a dozen regions along the Florida coast was ordered on Wednesday, according to the state's civil protection agency. Several other regions recommended evacuation for their residents.
Because of the approaching tropical storm, the US space agency Nasa had also rolled a rocket back into its hangar. She said she had previously canceled the launch of the unmanned lunar mission Artemis 1 scheduled for Tuesday.
"Ian" made landfall in western Cuba on Tuesday as a category 3 hurricane and, according to the weather service, raged in the region for five hours with wind speeds of more than 200 kilometers per hour before moving on to the Gulf of Mexico.
The hurricane caused a nationwide power outage in the Caribbean country. The Cuban Ministry of Energy spoke of an "extraordinary situation" and announced that the power supply would be gradually restored. According to Cuban state media, at least two people died in the Pinar del Río region as a result of the storm.
"Everything we own is damaged," said 65-year-old Caridad Fernández in Consolación del Sur, southwest of the capital, Havana. In the cigar stronghold of San Juan y Martínez, Hirochi Robaina of the Robaina tobacco plantation described the storm damage as "apocalyptic, a real disaster".
A few days ago, hurricane Fiona devastated parts of the Caribbean and Canada. At least ten people were killed.