Occasional light rains fell in the sprawling, mountain-cradled Haitian capital of Port-au-Prince, where more than 600,000 survivors of the 2010 earthquake are still living in fragile tent and tarpaulin camps.
Forecasters said Emily, the fifth named storm of the 2011 Atlantic hurricane season, could move across the Caribbean and possibly brush eastern Florida this weekend but with its core remaining offshore of the U.S. mainland.
Emily was about 60 miles south-southwest of the Haitian capital of Port-au-Prince at 2 p.m. EDT, the U.S. National Hurricane Center said.
The storm had sustained winds of 40 miles per hour and its center was expected to pass over southwest Haiti later on Thursday before tracking toward extreme eastern Cuba.
But Emily's movement across mountains on the Caribbean island of Hispaniola made up of Haiti and the Dominican Republic was "taking a toll" and the storm could "degenerate into a tropical wave later today," the center said in an afternoon advisory.
Haitian President Michel Martelly and civil defense officials issued public appeals for those living in low-lying or flood-prone areas of the hilly, quake-damaged capital to move to safer areas and not wait to be evacuated.
U.N. peacekeeping troops and civil defense authorities used buses to move some city residents from high-risk areas.
The Miami-based National Hurricane Center said Emily could dump as much as 20 inches of rain over parts of Haiti and the Dominican Republic.
As Emily moved over Haiti, authorities in the Dominican Republic issued flood alerts for some parts of the country after rainfall pushed up river levels.
Heavy rainfall poses a significant threat to Haiti, which is vulnerable to flash floods and mudslides because of its near-total deforestation. In June, at least 23 people were killed after rains unleashed flooding and mudslides.
Emily does not threaten oil and gas production facilities in the U.S. Gulf of Mexico. Some tracking forecasts show it crossing the Bahamas and approaching Florida by late on Saturday or early on Sunday.
While some earlier track predictions saw a possible south Florida landfall, others predicted the storm swinging north and staying away from the U.S. coast.
"Folks in eastern Florida should certainly be on their toes watching Tropical Storm Emily," said Dr. Gerry Bell, lead hurricane seasonal forecaster at the National Oceanic and Atmospheric Administration (NOAA).
Hurricane expert Jeff Masters of private forecaster Weather Underground said the further west Emily shifted, the larger the chance of the storm making landfall in Florida.
"If Emily's circulation can survive the mountains of Hispaniola and/or the terrain of Cuba, conditions are favorable for moderate intensification," Master wrote in his blog.
On Thursday, NOAA raised its outlook for activity in the 2011 Atlantic hurricane season, predicting it would produce between 7 to 10 hurricanes.
Three to five of those were expected to strengthen into "major" hurricanes of Category 3 or higher on the five-step Saffir-Simpson intensity scale, with top winds of at least 110 miles per hour, it said.
In May, NOAA projected 6 to 10 hurricanes.