The U.N. Mission in Haiti says it is preparing to distribute emergency supplies for more than 300,000 people in preparation for Tropical Storm Isaac.
It said some 5,700 U.N. troops stand ready to deploy once the storm passes to assess damage and clear roads for emergency response teams and evacuations.
Many people have refused to abandon their makeshift homes, apparently due to fears of theft, said Bradley Mellicker, head of disaster management for the International Organization for Migration.
"There's a lot of people who are resisting because they are scared of losing what little they have now," he said.
Many Haitians consider disaster an inevitable part of life in the poorest country in the Americas.
"We live under tents. If there's too much rain and wind, water comes in. There's nothing we can do," said Nicholas Absolouis, an unemployed 34 yea -old mechanic at one camp for homeless people on the north side of the capital.
"If he's coming, he's already on the way," added Juliette Jean-Baptiste, 26, another resident of the camp. "Our tents leak already."
Flooding could also help rekindle a cholera epidemic in Haiti, which has killed more than 7,500 people since the disease first appeared in October 2010, foreign aid workers said.