Governments in the northeast Caribbean urged islanders to prepare for Hurricane Irma, a potentially catastrophic Category 5 storm that was forecast to begin buffeting the region as soon as late Tuesday, and could also affect Puerto Rico and Florida by the weekend.
Irma's winds strengthened to 185 mph on Tuesday morning, the U.S. National Hurricane Center reported, making it one of the most powerful storms ever observed. Its wind strength was almost off the charts, far surpassing the 157 mph threshold for a Category Five storm on the Saffir-Simpson scale. There is no Category Six.
Forecast track models show Irma will graze the coast of Puerto Rico and Cuba before turning north over the Florida Keys and into the Gulf of Mexico. But experts say the models can't be fully trusted at this stage and a small change could put Irma over heavily populated South Florida, home to more than six million people.
Irma poses the most serious hurricane threat to northern Cuba and Florida since at least Hurricane Andrew (1992), according to meteorologist Jeff Masters with Weather Underground. Hurricane-force winds extend outward up to 50 miles from the center and tropical-storm-force winds extend outward up to 175 miles.
Puerto Rico's San Juan airport cancelled 85 flights on Wednesday, about 40 percent of services. The island's governor Ricardo Rossello described the hurricane to reporters as "something without precedent" for the island of 3.4 million people.
Miami-Dade County announced it was closing all its publicly run schools and offices on Thursday and Friday.
" Satellite images on Tuesday morning showed a spectacular hurricane with a large eye surrounded by extremely intense eyewall thunderstorms," said Masters.
Irma's winds are the most powerful ever measured in an Atlantic hurricane outside the Caribbean and east of the Gulf of Mexico, Masters added. He cited a table of the strongest hurricanes by Phil Klotzbach at Colorado State University showed Irma was tied with Wilma (2005) and Gilbert (1988) as the second strongest hurricane in Atlantic records going back to 1851.
Emergency officials in the Caribbean warned that Irma could dump up to 10 inches (25 centimeters) of rain, unleash landslides and dangerous flash floods and generate waves of up to 23 feet (7 meters) as the storm draws closer.
A hurricane warning was issued for Antigua and Barbuda, Anguilla, Montserrat, St. Kitts and Nevis, St. Martin, Saba, St. Eustatius, St. Maarten and St. Barts.
"We're looking at Irma as a very significant event," Ronald Jackson, executive director of the Caribbean Disaster Emergency Management Agency, said by phone. "I can't recall a tropical cone developing that rapidly into a major hurricane prior to arriving in the central Caribbean."
Florida and Puerto Rico have also declared a state of emergency to help prepare for Irma. The latest forecast models predict Irma could miss a direct hit on heavily populate south Florida as the storm is pushed further west before sharply turning north early next week up the Gulf of Mexico towards north west Florida.
A hurricane watch was in effect for Puerto Rico, Vieques, Culebra, the British and U.S. Virgin islands and Guadeloupe. A tropical storm watch was issued for Dominica.
Antigua and Anguilla shuttered schools on Monday, and government office closures were expected to follow.
On the tiny island of Barbuda, hotel manager Andrea Christian closed down the Palm Tree Guest House as Irma approached. She said she was not afraid even though it would be her first time facing a storm of that magnitude.
"We can't do anything about it," Christian said by phone, adding that she had stocked up on food and water. "We just have to wait it out."
Antigua Prime Minister Gaston Browne urged preventative measures such as cleaning drains and securing objects that could be sent flying by high winds. Workers began pruning branches that could potentially tear down utility lines.
Latye Tuesday the U.S. hurricane center said Irma was centered about 50 miles east of Antigua and moving west at 15 mph.
Puerto Rico Gov. Ricardo Rossello said 4 inches to 8 inches (10-20 centimeters) of rain were expected, as well as winds of 40-50 mph with gusts of up to 60 mph. He warned of flooding and power outages.
"It's no secret that the infrastructure of the Puerto Rico Power Authority is deteriorated," Rossello said. He activated the National Guard, canceled classes for Tuesday and declared a half-day of work.