MIAMI -- Tropical storm Dennis swiped the island nations of Cuba and Jamaica Saturday, threatening the Florida Keys, and forecasters said the storm could become a hurricane by Sunday.
The storm's center was reforming near the north coast of Cuba, according to the National Hurricane Center, and the threat to the Florida Keys had increased.
'I think it is possible Dennis will become a hurricane by Sunday sometime,' hurricane forecaster Joe Pelissier said.
Top sustained winds were 40 miles per hour but Pelissier said the storm was expected to gain in strength as it passed Cuba.
The storm's motion became erratic over Cuba but it appeared to be moving toward the north northwest at 8 mph, forecasters said.
The advisory warned all residents in extreme South Florida to monitor Dennis closely and those in the Keys to be prepared to take quick action if warnings were issued.
'Small craft around extreme south Florida should exercise caution and those in the lower keys should stay near safe harbor,' an advisory said.
Dennis formed in the far east Atlantic last weekend and by Monday had 65-mph winds. It appeared destined to reach hurricane force at that time, but it then broke up into a band of disorganzied clouds as it moved through the windward islands of the Caribbean.
The disturbance began regaining strength Friday and was again designated a tropical storm Saturday morning.
The hurricane center officially redesignated Dennis a tropical storm in its noon advisory, which reported its highest sustained winds had hit 45 mph. Winds were higher in squalls.
Forecaster Bob Sheets said heavy rains over Cuba would continue at least through Sunday and were spreading into the Florida Keys Saturday night. Residents of Marathon in the Florida Keys reported heavy rain and gusts up to 35 miles an hour.
Dennis poured up to 7 inches of rain on Jamaica and officials estimated at least 50 people lost their homes as scores were evacuated from flooded areas.
At 9 p.m. EDT Saturday, Dennis was located over Cuba near latitude 22.5 north and longitude 80.5 west, or about 130 miles east southeast of Havana.