PORT-AU-PRINCE (AFP) - Haiti hunkered down Friday as forecasters warned that Tropical Storm Isaac could dump large amounts of rain on the impoverished country still recovering from a killer earthquake.
Packing maximum sustained winds of 75 kilometers (45 miles) per hour, Isaac was centered some 265 kilometers south of Santo Domingo in the Dominican Republic at 0900 GMT, the Miami-based US National Hurricane Center said.
"Tropical storm conditions are expected over portions of the Dominican Republic and Haiti today," it said.
Earlier Friday, the NHC had projected that parts of Haiti could see hurricane conditions.
The fierce weather could spell misery for the roughly 400,000 residents of the western hemisphere's poorest country who live in makeshift squatter camps two years after the earthquake that killed an estimated 250,000 people.
"They remain amongst the most vulnerable, should the storm hit the city," said Jean-Claude Mukadi, Haiti's national director for the humanitarian group World Vision.
"Without a stable sanitation system or permanent housing, heavy rain and wind can create much larger problems like disease from water contamination," he added.
Residents in the neighboring Dominican Republic and nearby Puerto Rico rushed to erect defenses against the expected wind and rain, set to churn on to Cuba and the southern United States by the weekend.
The NHC said the eye of the storm would near or pass over Hispaniola, the island shared by Haiti and the Dominican Republic, on Friday before heading to southeastern Cuba, home to the US naval base at Guantanamo Bay, on Saturday.
Isaac could reach Florida as a hurricane early next week, just in time for the Republican Party's National Convention.
"Some strengthening is forecast while the center remains over water," the NHC said.
Republican delegates from around the country will be in Tampa for four days to formally nominate former Massachusetts governor Mitt Romney to challenge President Barack Obama in the November 6 election.
City officials have urged residents to prepare for the worst, and Republican National Committee chairman Reince Priebus has expressed concern about the storm but insisted the show would go on.
Isaac is approaching Florida as the state marks the 20th anniversary of Hurricane Andrew, a maximum level category five storm that killed 26 people and left some $26 billion in material damage.
Governor Rick Scott, while stressing that it was still early to predict Isaac's path, urged Florida residents to prepare for the worst, saying: "Every family should be prepared to sustain themselves for up to 72 hours."
Isaac could dump up to 20 inches (51 centimeters) of rain on Hispaniola, the NHC said, adding: "These rains could cause life-threatening flash floods and mudslides."
Classes were canceled and hospitals boosted their staff levels in at-risk areas of the Dominican Republic. Authorities have urged locals to prepare to face floods, rising waters and mudslides due to heavy rains.
In southwestern Puerto Rico, locals stocked up on water, fuel and supplies ahead of the storm, and restaurants, hotels and homes tied down outdoor chairs and tables. Heavy rain could be seen far out to sea.
Several hundred people were evacuated Thursday from Guantanamo, which houses the alleged September 11 plotters and other detainees from the so-called "war on terror."
Legal proceedings against the alleged masterminds of the 2001 attacks on New York and Washington were postponed as the base buckled down for the storm.
Meanwhile, forecasters said former tropical storm Joyce was now a weak tropical depression situated about 1,785 kilometers east of the Leeward Islands.