A waiting game for Tropical Storm Isaac

Most of Florida remained inside Tropical Storm Isaac’s very broad risk “cone’’ on Thursday morning, but the threat to a string of Caribbean nations was clearer, more immediate and serious.

The biggest concern was Haiti. The capital city of Port-au-Prince, where some 400,000 earthquake refugees still live in tents, sat dead-center in Isaac’s path. Beginning Friday, Haiti and the Dominican Republic could both see a foot or more of rain. Far less has historically triggered deadly flooding and mud slides.

The storm appeared to have spared Puerto Rico, but authorities feared that the storm's slow pace could flood cities around the island, as the storm lasts longer than expected.

“We are worried about flooding," Gov. Luis Fortuño said at an early morning press conference. "The storm slowed to 12 mph, so we could be getting a lot of rain in the next 12-24 hours. We ask the citizenry: don't lower your guard."

By 6 a.m., only 58 people had turned to one of the island's 422 shelters. The vast majority of the island still had water and power, he said. All the ports in the south remained closed, although the San Juan port remained open. Flights to the Caribbean were canceled. Fortuño said Isaac had claimed one victim, a woman preparing her home in Bayamon had slipped and fallen off a second floor.

It appeared increasing likely that South Florida would feel some effect from Isaac, but whether it would amount to soggy side-swipe or a damaging direct hit from a hurricane remained uncertain, said Robbie Berg, a hurricane specialist at the National Hurricane Center in West Miami-Dade County.

“Really, the whole state of Florida has an equal chance of feeling tropical storm-force winds,” Berg said. That includes Tampa, where the Republican National Convention is scheduled to begin Monday in a low-lying section of the city vulnerable to storm surge. If the center’s forecast remained unchanged, which is unlikely, Isaac would be churning just off the coast early Tuesday.

Gov. Rick Scott said state and local emergency managers were monitoring the storm and had contingency plans in the event of a hurricane threat or evacuation.

“I am confident in our preparation, and the decision process in place to ensure the safety of both our residents and visitors during the convention,” Scott said in a statement.

Emergency managers in Miami-Dade, Broward and Monroe counties were also watching Isaac closely but said it would take another day, or even two, to evaluate the threat from the storm. Curtis Sommerhoff, Miami-Dade’s director of emergency management, said some special needs residents, such as the elderly or infirm, might be moved along with mobile home residents, but he didn’t anticipate a large evacuation unless significant strengthening is forecast.

“I don’t think we’ll be concerned about [storm] surge with the current scenario,” he said.

Isaac’s maximum winds dropped to 40 mph overnight and forecasters shifted its poorly defined center slightly south. But they still expected the massive storm to begin drawing power from the warm Caribbean over the next few days, potentially reaching Category 1 wind speeds before it strikes Hispaniola on Friday. But the mountains of Haiti, as well as a passage across Cuba, could knock at least some of the air out of Isaac, Berg said. The hurricane center expects it to exit the coast of Cuba early Sunday as a tropical storm, with a chance of re-strengthening into a Category 1 hurricane as it approaches the Florida Keys.

Whether Isaac skirts the Gulf or Atlantic coasts or makes landfall, the storm is large enough that its outer bands will likely be felt somewhere in South Florida, Berg said.

In the Caribbean, Haiti’s Office of Civil Protection and National Meteorological Center warned residents in flood-prone areas to monitor the radio and "remain vigilant."

In advance of the storm, Puerto Rico suspended classes Wednesday and closed all government offices except those engaged in emergency operations and the governor declared a state of emergency.

Eight flights were canceled from San Juan to neighboring Caribbean islands. The airport was not expected to close Thursday although airlines could cancel flights.

Warning Coordinator Meteorologist Ernesto Morales said the storm’s outer bands were already being felt in the afternoon, with gusts of up to 37 mph detected at San Juan’s airport about 5 p.m. Wednesday. He said the storm promises plenty of rain island-wide, from four to six inches and up to 10 inches possible in some areas.

In Cuba, the Pentagon is evacuating about 200 people -- lawyers, staffers, 911 victims -- from the U.S. Navy base in Guantánamo on Thursday in advance of the arrival of Isaac at Guantánamo. They all were brought to the base earlier this week for a hearing in the Sept. 11 terror trial that the judge cancelled in consideration of the storm.

The Cuban Institute of Meteorology also put out advisories about the storm and Radio Havana Cuba reported that Isaac "represented a potential danger to the island,’’ but for the most part, the Cuban media stuck to disseminating the advisories. The closest Cuban city to the storm track is Baracoa on the mountainous eastern tip of the island, just across the Windward Passage from Haiti. The last time Baracoa was affected by a hurricane was Nov. 5, 2010, when Hurricane Tomas passed just east of the small city with 80 mph winds and caused a minor storm surge.

Miami Herald staff writers Jacqueline Charles and Carol Rosenberg, reporting from Guantánamo, contributed to this story.