U.S. forecasters said Isaac was likely to approach Hispaniola, the island shared by the Dominican Republic and Haiti, as a hurricane late Thursday or early Friday after intensifying over the warm waters of the Caribbean Sea. It was predicted to move on to Cuba as a tropical storm and perhaps eventually menace Florida as a hurricane later in the week.
By Wednesday evening, the storm was 65 miles (110 kilometers) southwest of the French Caribbean island of Guadeloupe, with maximum sustained winds of 45 mph (75 kph). Isaac was moving west at 21 mph (33 kph), the U.S. National Hurricane Center said.
At the bar of the Fort Young Hotel in Dominica's coastal capital of Roseau, a few tourists and locals spent the evening drinking cold beer and chatting over the sound of white-crested waves just outside.
"The skies were very black and cloudy most of the day, but it's been pretty quiet so far. Some rain, very little wind," bartender Raymond Reynolds said at the 71-room hotel on the jagged, densely forested island. "We've been through this before."
In the foothills of Dominica's Morne Aux Diables volcano, Tess Hunneybell, owner of Manico River Eco Resort, said most of the day was "weirdly quiet" after she and others wrapped the resort's signature treehouses in tarpaulin and nailed shut louvre doors.
As a precaution, Prime Minister Roosevelt Skerrit urged people to stay home from work Wednesday. "I want us all to be safe," he said. "I don't want lives to be lost."
As the storm approached, military authorities at the U.S. base in Guantanamo Bay, Cuba, canceled several days of pretrial hearings in the case of five prisoners charged in the Sept. 11 attacks. They also planned to evacuate about 200 people, including legal teams and relatives of Sept. 11 victims.
Isaac also posed a possible threat to Florida during next week's Republican National Convention in Tampa, according to forecasters, though the storm's track was uncertain.
In the U.S. Virgin Islands, along the harbor in St. Croix's historic town of Christiansted, piers normally lined with pleasure boats were empty Wednesday. Business owners stacked sandbags around the doorways of the pastel-colored buildings that line the narrow streets. One bar advertised a "hurricane party."
Lia Studdard, who owns a 40-foot boat moored in the harbor, planned to spend the storm holed up in a hotel room with a view of her vessel.
"I don't think it's going to be as bad as everyone expects," Studdard said. "Worst case scenario, I'll take my dinghy and go out and drop another anchor."
The U.S. Virgin Islands commissioner of public works, Darryl Smalls, said crews distributed sandbags to residents in St. Croix, where schools and government offices were ordered to remain closed Thursday. St. Kitts announced similar closures for Wednesday.
On the U.S. island of Puerto Rico, Gov. Luis Fortuno declared a state of emergency and activated the National Guard. He also canceled classes and closed government agencies. Federal officials closed the popular San Felipe del Morro castle in Old San Juan. The storm was expected to pass just south of Puerto Rico on Thursday.
Authorities in Puerto Rico reported that a 75-year-old woman died Wednesday in the northern city of Bayamon when she fell from a second-floor balcony while filling a barrel with water in preparation for the storm.
The U.S. Coast Guard closed all ports in Puerto Rico and the U.S. Virgin Islands to incoming commercial ships and warned that all commercial vessels bigger than 200 gross tons must leave or obtain permission to remain in port.
As he campaigned in Nevada, President Barack Obama received an update from the Federal Emergency Management Agency on U.S. preparations for Isaac, deputy press secretary Josh Earnest reported.
"FEMA has been in close coordination with local officials and emergency managers in Puerto Rico and the U.S. Virgin Islands," Earnest told reporters as Obama flew to a later stop in New York. Earnest said FEMA had deployed teams to both locations.
The storm unleashed downpours on the French island of Guadeloupe on Wednesday, said local chief meteorologist Norbert Aouizerats. In Martinique, officials warned of swollen rivers and flooding. Meteorologist Jean-Noel Degrace said at least 3 inches (8 centimeters) of rain had fallen Wednesday morning. The leader of Martinique, Laurent Prevost, urged people in low-lying areas to evacuate, but there were no immediate reports of damage.
In the Dominican Republic, authorities banned boats from entering its waters and warned of heavy rains from Thursday through Saturday.
Liat airline and American Eagle canceled flights to islands including Dominica, the U.S. Virgin Islands, Guadeloupe and Martinique.
On the island of Vieques, which lies just east of Puerto Rico, people prepared for the government to temporarily shut off power.
Glenn Curry, an owner of Bananas Guesthouse, said he closed the restaurant and would move guests to a higher floor.
"I don't think this is going to be a major storm, but it's going to be noisy and unpleasant for a few hours," he said.
Associated Press reporters Jason Bronis in Christiansted, St. Croix; Danica Coto in San Juan, Puerto Rico; David McFadden in Kingston, Jamaica; Rodolphe Lamy in Fort-de-France, Martinique; and Mark S. Smith in Washington contributed to this report.