Hurricane Charley drenched Jamaica as it moved through the Caribbean toward Key West while Tropical Storm Bonnie is poised to strike the northwest of Florida.
The twin storms put millions of people on alert in the Caribbean and on the Florida peninsula, and forced the evacuation of oil rigs in the Gulf of Mexico.
Charley had sustained winds of 121 kilometres per hour, just at the threshold for hurricane status, as it passed south of Jamaica and headed toward the Cayman Islands and Cuba. It is expected to hit the low-lying Florida Keys by Friday, the US National Hurricane Center said.
Rainfall of up to 15 centimetres caused flooding and mudslides in some villages of eastern Jamaica, but there had been no reports of casualties by nightfall.
Hurricane or tropical storm alerts were in force for parts of Haiti, Jamaica, the British colony and offshore finance center of the Cayman Islands, Cuba and Florida.
Although attention focused on Charley because of its strength, the more immediate threat was the looming arrival of Tropical Storm Bonnie - potentially as a brief hurricane - in the relatively sparsely populated Florida Panhandle this morning.
Energy companies evacuated workers from 108 production platforms and 37 rigs in the Gulf of Mexico.
Florida Governor Mr Jeb Bush declared a state of emergency and around 8,000 National Guardsmen were on alert.
Authorities in the Florida Keys ordered visitors to pack up and go before the arrival of Charley.