Tropical Storm Isaac has killed at least four people in different parts of Haiti, with more than 4,000 people still remaining in temporary emergency shelters.
Lashing rains and gale-force winds and high winds were reported along parts of the country on Saturday. The impoverished Caribbean nation is still reeling from the effects of a devastating 2010 earthquake that killed more than 250,000 people.
In addition to those in temporary shelters, more than 350,000 survivors of the last earthquake are still living in fragile tent and tarpaulin camps near the capital.
Intermittent power outages affected the greater areas of the capital city of Port-au-Prince area as Isaac bore down on the impoverished Caribbean country.
The storm had sustained winds of 110 kmh and its centre was expected to pass over Haiti's southern coast.
Life-threatening flash-floods and mudslides, which are common in Haiti, could add to the misery of the displaced Haitians.
The storm was forecasted to "move near or over southeastern Cuba on Saturday, move near or over central Cuba on Saturday night and approach the Florida keys on Sunday", the US-based National Hurricane Center (NHC) said in its 21:00 GMT bulletin on Friday.
Long lines had formed outside supermarkets in the Haitian capital on Friday as people filled stores to stock up on supplies.
Those still without proper shelter after the quake "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."
President Michel Martelly, who canceled a trip to Japan, earlier took to the airwaves with safety advice and to urge Haitians to follow the directions of civil defence personnel.
Laurent Lamothe, the Haitian prime minister, said the whole government, including security forces, has mobilised to prepare for the storm.
"We are going to work with our international partners to co-ordinate response actions," Lamothe said.
The Haiti director for Oxfam, another humanitarian group, said that his group was preparing clean water and hygiene kits to help prevent the spread of cholera and other water-borne diseases.
Haiti has always struggled to cope with the aftermath of natural disasters. Deforestation has made the country highly vulnerable to landslides and flash flooding.
"These rains could cause life-threatening flash floods and mudslides," the NHC said.
If this storm follows the forecast, then it will cause widespread flooding and potentially landslides as well.
Residents in the neighbouring Dominican Republic and on nearby Puerto Rico rushed to erect defences against the expected wind and rain, set to sweep on to Cuba and the southern US by the weekend.
Isaac has already churned over the tiny Caribbean islands of Guadeloupe, Martinique and Dominica.
Flights were canceled, and some restaurants were closed, but fortunately Isaac was not particularly powerful when it hit the islands. Generally, the winds were under 75kph, and no more than 80mm of rain was reported.
As a precaution, hearings at the US military base at Guantanamo Bay in Cuba have been postponed.
It is thought Isaac may hit Florida on Monday, the same day the Republican National Convention starts.