For Haiti, Isaac’s rains are what will add to the misery of some 400,000 refugees of the 2010 earthquake who still live in makeshift tent cities around the capital.

The danger from flash floods and mudslides is even greater outside the capital, where crumbling hillsides stripped of vegetation have made much of the country’s often poorly built homes vulnerable to floods and lethal landslides. Storms in 2008 left hundreds dead and thousands homeless. In 2004, Tropical Storm Jeanne killed some 3,000 people in Gonaives when three rivers spilled over.

Forecasters are predicting from eight to 12 inches of rain across Haiti, with up to 20 inches in some spots.

Haiti’s government mobilized disaster committees and warned the entire country could be affected.

“Do not panic,” Prime Minister Laurent Lamothe said. “Panic can create more problems. It’s best to remain calm.”

Isaac appeared to have spared the Virgin Islands and Puerto Rico of serious damage, but authorities feared there still could be flooding,

In Cuba, the news agency Prensa Latina reported civil defense agencies in the eastern part of the country have been activated and are in the process of evacuating people from low-lying areas and protecting “economic and social’’ resources.

Tropical Storm Joyce also formed Thursday briefly, but forecasters downgraded it to a depression at 11 p.m. and expected it to curve into the Atlantic — with only Bermuda potentially in its path early next week.

Miami Herald staff writers Toluse Olorunnipa in Tallahassee, Frances Robles in San Juan, Cammy Clark in the Keys and Mimi Whitefield in Miami contributed to this report.