The system had top sustained winds near 35 mph and was expected to strengthen into Tropical Storm Nicole later on Wednesday, the U.S. National Hurricane Center said.
“The depression is very near becoming a tropical storm,” the center said in a 5 a.m. ET advisory.
Tropical cyclones become named storms when their sustained winds reach 39 mph (63 km per hour).
The system was centered about 190 miles south of Miami and was moving north-northeast at 14 mph/22 kph, the Miami-based hurricane center said. It was expected to move over the Florida Straits later in the morning.
The storm was projected to stay well clear of the Gulf of Mexico, where U.S. oil and gas operations are concentrated. The heaviest rains were on the east side of the system, which would reduce the threat to the central Florida orange groves.
The system was not expected to strengthen beyond a minimal tropical storm and forecasters predicted it would dissipate into a wide blob of thunderstorms by the weekend.
The main threat was from flash flooding and mudslides. The depression was expected to dump 5 to 10 inches of rain in its path, including over the Cayman Islands, Jamaica and Cuba.
A tropical storm warning was in effect along the Florida eastern coast, the Cayman Islands and parts of Cuba and the Bahamas. A warning means tropical storm conditions were expected between 12 to 24 hours.