This satellite image taken early Wednesday shows a tropical depression forming in the northwestern Caribbean Sea. ((Weather Underground/Associated Press))

Tropical storm Nicole has lost strength over the Florida Straights, the U.S. National Hurricane Center said, but not before causing deadly flooding in Jamaica.

A family of six and two elderly men drowned in Jamaica during the storm, Reuters reported.

The hurricane centre said while the storm isn't a risk for the U.S., it continues to pose a flooding risk for Cuba, the Cayman Islands, Jamaica and the Bahamas.

Tropical storm Nicole started blowing over Cuba early Wednesday, after developing quickly from a tropical depression in the Caribbean, and was headed toward southeastern Florida.

Early Wednesday, the storm's centre was about 160 kilometres south of Marathon, Fla., moving north-northeast at 22 km/h, according to the U.S. hurricane centre, which is in Miami.

Maximum sustained winds were 55 km/h, but the storm has since strengthened to a tropical storm. It was expected to be near or over southeastern Florida by Wednesday evening.

Jose Rubiera, Cuba's chief meteorologist, said the weather system was large but disorganized and weak. He predicted the rainfall would cause more problems in some mountainous regions and low-lying areas than the winds associated with the storm.

'Don't be afraid'

"Don't be afraid," Rubiera said during the Tuesday evening newscast on state television, pointing to a model showing dark moisture associated with the storm moving over the heart of the island. "This means little in practical life."

He went on to forecast that top wind speeds would rise to no more than 80 km/h.

"Those winds will not cause any damage, except possibly to sensitive crops or weak structures," he said.

An official bulletin issued by the government warned citizens in areas facing heavy rains to be especially vigilant, keeping a close eye on the storm's trajectory.

Cuba has a well-trained civil defence force noted for its fast response to natural disasters. The country often orders large-scale evacuations ahead of even moderate storms. But no such evacuations were immediately announced this time, and state media had no word on the activation of emergency plans.

While the 2010 Atlantic hurricane season has been unusually active, tropical storm Nicole is the first to directly threaten Cuba. The island was devastated by three hurricanes in 2008 but was spared last year.

Serious damage from a hurricane this year could be a major blow to the cash-strapped government as it attempts to right its weak economy. This month, Cuba's communist leaders announced that 500,000 state employees would be laid off and reforms implemented to allow more private enterprise.

A tropical storm warning was in effect from Matanzas province eastward to Ciego de Avila in Cuba, as well as the northwestern and central Bahamas and in Florida from Sebastian Inlet to the Keys.