Hanna's maximum sustained winds slipped to 70 mph (110 kph), but the U.S. National Hurricane Center in Miami said it could regain hurricane strength of 74 mph (119 kph) within a day. Forecasters say it could hit the U.S. coast by Friday or Saturday.
"It is important to note that Hanna is expected to continue to intensify" before it hits land, the U.S. National Hurricane Center said Tuesday morning. "Hanna could be a major hurricane."
Forecasters said the storm could hit the U.S. anywhere from Florida to North Carolina -- and projections indicated it could then spread rain into the Northeast even after it weakens. "There is an extremely high uncertainty associated with this storm," said Karina Castillo, a meteorologist with the hurricane center.
Hanna's movement has been agonizingly slow for people in the tourist magnets of the Bahamas and the Turks and Caicos, directly under its winds.
The storm was near Great Inagua island in the Bahamas Tuesday morning and was expected to slowly roll across it throughout the day.
The storm had not caused major injuries on the island, home to about 1,000 people, but it knocked out power, downed trees and tore shingles from roofs, said Stephen Russell, interim director of the Bahamas National Emergency Management Agency.
"I'm not anticipating any major structural damage," Russell said.
Newly formed Tropical Storm Ike was cruising westward across the Atlantic and was projected to near the storm-weary Bahamas by Sunday. It had winds of 50 mph (85 kph) and was expected to grow stronger.
A man from Colombia died and a Brazilian woman was missing on Monday after they were swept away in a river swollen by Hanna's rains. The two were students at the University of Puerto Rico on a trip to the island's east.
People living near the northwestern Haitian city of Gonaives told Radio Caraibes that floods there sent residents fleeing to their roofs.
More than 8,000 Haitians remain homeless in the wake of Hurricane Gustav, which was downgraded to a tropical storm as it moved over central Louisiana late Monday.
At least 95 people have been killed by storms in Haiti in the last month alone.
Hanna prompted NASA to put off shifting the space shuttle Atlantis from an assembly building at Florida's Kennedy Space Center to the launch pad for at least a day. The move had been scheduled for Tuesday in preparation for an October mission to the Hubble Space Telescope.