The storm that had been drifting south and east finally swung toward the north on Wednesday and authorities issued a hurricane warning for northwest and central Bahamas.
Hanna was expected to sweep across the Bahamas and then start climbing along the U.S. coastline by the weekend, according to the U.S. National Hurricane Center in Miami with a 20 percent chance it could bring tropical storm force winds to New York City.
Haitian authorities on Wednesday reported five more deaths caused by Hanna, raising the toll to 26.
Floodwaters swamped a hospital in the Les Cayes area, forcing nurses to move patients to higher floors. At least 5,000 people in Les Cayes remained in shelters, said Jean-Renand Valiere, a coordinator for the civil protection department.
High water still prevented U.N. soldiers from reaching the western city of Gonaives, where the rise of muddy water drove people to seek refuge on rooftops Tuesday as wind gusts drove horizontal sheets of rain.
"They are screaming for help," said Iris Norsil, 20, who managed to escape the city.
Water rose so much overnight near Gonaives that a bridge people crossed on Tuesday night was under water on Wednesday.
A convoy carrying Prime Minister Michele Pierre-Louis had to abandon efforts to reach Gonaives when one of the cars was nearly swept away, said Julian Frantz, a Haitian police officer with the group.
"The situation is as bad as it can be," said Vadre Louis, a U.N. official in Gonaives. "The wind is ripping up trees. Houses are flooded with water. Cars can't drive on the street. You can't rescue anyone, wherever they may be."
Haiti already had suffered scores of deaths due to flooding cause by Tropical Storm Fay and Hurricane Gustav in late August.
Hanna was centered about 60 miles west-northwest of Grand Turk Island Wednesday afternoon, with maximum sustained winds of near 60 mph (95 kph), the hurricane center said. Tropical storm force winds extended out as far as 290 miles in some areas.
It was moving north at about 12 mph and it was expected to cut through or near the central and northeastern Bahamas over the next couple of days. It could regain hurricane force by Thursday.
Rain and wind were picking up in the Bahamas, where officials told residents they would shut down the water system Wednesday night.
"Even though we're not feeling the full effects of the storm, it is rough out there," said Chrystal Glinton, a spokeswoman for the National Emergency Management Agency. "Persons have been warned to stay indoors. That's what they're doing. Waiting."
Haiti is particularly vulnerable to devastating floods because of its steep hillsides that have been deforested to plant crops or make charcoal.
Meanwhile, Ike strenghtened into the fifth hurricane of the Atlantic season as it cruised northwestward at 18 mph across the Atlantic with top winds near 80 mph. Forecasters cautioned that "it is too early to determine what, if any land areas might be directly affected by Ike."
Ike was located 670 miles east-northeast of the Leeward Islands.
Following behind was Tropical Storm Josephine, which grew slightly weaker, with top winds near 60 mph.
And in the Pacific, Tropical Storm Karina weakened to a fading tropical depression on Tuesday.