MIAMI -- Hurricane Irma has strengthened into an "extremely dangerous" Category 5 storm, the National Hurricane Center said Tuesday, threatening to slam into northeastern Caribbean islands and Puerto Rico by Wednesday before possibly taking aim at the U.S. mainland.
Irma was churning Tuesday morning in the Atlantic about 270 miles east of Antigua and Barbuda, heading west with maximum sustained winds of 175 mph -- well above the 157 mph threshold for a Category 5 -- the hurricane center said.
The storm's forecast track has it near or over Antigua and Barbuda by late Tuesday or early Wednesday, and the Virgin Islands and Puerto Rico on Wednesday afternoon.
"Some fluctuations in intensity are likely during the next day or two, but Irma is forecast to remain a powerful Category 4 or 5 hurricane during the next couple of days," the center said.
It is still too early to tell the exact impact Irma will have on the United States.
Computer models show the system eventually heading toward Cuba and possibly turning north toward Florida by the weekend.
While Irma's exact path is uncertain, several islands in the Caribbean as well as Florida are bracing for the storm.
After declaring a state of emergency all across Florida, Gov. Rick Scott said President Donald Trump had "offered the full resources of the federal government as Floridians prepare for Hurricane Irma."
"In Florida, we always prepare for the worst and hope for the best, and while the exact path of Irma is not absolutely known at this time, we cannot afford to not be prepared," Scott said in a statement.
Hundreds of people rushed to the stores in Puerto Rico, emptying shelves of food and drinking water just as the governor of Puerto Rico, Ricardo Rossello, declared a state of emergency and activated the National Guard on Monday.
For hours, people also lined up outside hardware stores hoping to get plywood, batteries and power generators. If Irma knocks out power, Puerto Ricans said they are worried it would take weeks or months before the power is restored.
"(Power) is something absolutely necessary, especially due to Puerto Rico's weather. We need to have the A/C or a fan on all night," a woman told WAPA.
Last month, the director of Puerto Rico's power utility Ricardo Ramos Rodríguez, said several factors have made the island's electric system "vulnerable and fragile," WAPA reported.
One of those factors is the shortage of employees. Many workers recently retired or left their jobs for better prospects in the U.S. mainland, Ramos Rodríguez said.
Public schools and officials at the University of Puerto Rico campuses have canceled classes, and many businesses remain closed.
Puerto Rico and a string of Caribbean islands are under hurricane warnings, including the British and U.S. Virgin Islands, Antigua, Barbuda, Anguilla, Montserrat, St. Kitts, Nevis, Saba, St. Eustatius, St. Martin/Sint Maarten and St. Barts, the hurricane center said.
By the weekend, it's possible Irma could start heading to the eastern coast of Florida and also farther up the East Coast, Javaheri said.
"Everyone wants to see this at least meander away from the United States. The strength, the positioning, the timing of that troughs coming in to the eastern coast line will dictate exactly where Irma ends up," Javaheri said.
In Miami, supermarkets are already selling out on water and nonperishable food. People are trying to beat the rush in case Irma makes landfall in Florida.
"I've been through hurricanes and they're like 'oh it's going to hit right here' and then it hits 30, 40 miles up the coast and it kind of changes the way everything goes so, better safe than sorry," Florida resident Greg Andrews told WPLG.