Tropical Storm Isaac getting better organized in the Atlantic as it approaches the Caribbean

ROSEAU, Dominica — Leaders across much of the Caribbean closed schools and government offices on Wednesday and urged people to stay at home as Tropical Storm Isaac swept toward the region, threatening to soon become a hurricane and perhaps eventually to menace Florida.

The storm was 210 miles (340 kilometers) east of the French Caribbean island of Guadeloupe on Wednesday morning with maximum sustained winds of 45 mph (75 kph). Isaac was moving west at 19 mph (31 kph) and was expected to become a hurricane by Thursday, according to the U.S. National Hurricane Center.

In Dominica, one of the first islands in the storm's path, Prime Minister Roosevelt Skerrit urged people to stay home from work on Wednesday.

"I want us all to be safe," he said. "I don't want lives to be lost. I have listened to the advice of the experts and so I am asking all to stay indoors."

In Puerto Rico, Gov. Luis Fortuno declared a state of emergency and activated the National Guard. He also canceled classes and closed government agencies on Wednesday. The U.S. Coast Guard ordered all commercial vessels bigger than 200 gross tons to leave the port or obtain permission to remain in port.

The Liat airline said it expected to cancel flights to and from Dominica by Wednesday afternoon, and American Eagle has already canceled all its flights, according to Benoit Bardouille, CEO of the island's Air & Seaport Authority. The fast ferry that runs to Guadeloupe and Martinique also will temporarily suspend service, he said.

Disaster Coordinator Don Corriette warned of landslides and asked people in low-lying areas to seek shelter if needed.

The storm's center was expected to move over the Leeward Islands on Wednesday evening, and forecasters said it is expected to hit the Dominican Republic, Haiti and Cuba as a hurricane later in the week.

Isaac also poses a possible threat to Florida during next week's Republican National Convention in Tampa.

Tropical storm warnings are in effect for Puerto Rico, the U.S. and British Virgin Islands and a swath of islands across the Caribbean including Martinique, Dominica, Guadeloupe, St. Martin, St. Kitts, Nevis, Antigua, Barbuda, Montserrat, Anguilla, Saba, St. Eustatius, St. Maarten, Culebra and Vieques.

A hurricane watch is in effect for Puerto Rico, Vieques, Culebra, the U.S. and British Virgin Islands and the south coast of the Dominican Republic.