MIAMI (CBS/AP) - Forecasters expect the storm, which is packing heavy rain and 60-mph winds, to move over Cuba today and become a hurricane tomorrow.

Florida Gov. Rick Scott declared a state of emergency and officials urged vacationers to leave the Florida Keys, after forecasters expanded hurricane warnings and watches for parts of Florida, just as the Republican Party gathers for its national convention in Tampa.

CBS News hurricane consultant David Bernard reports there is great concern in South Florida and the Keys - and for the rest of the peninsula as well - as the storm approaches.

Late Saturday morning the storm was about 40 miles east of Guantanamo, Cuba, moving northwest at 17 mph. Bernard says the future track of Isaac brings it to a category 1 on Sunday afternoon, with the possibility of becoming even stronger than that.

By Monday night or Tuesday morning, it will make its closest approach to the west coast of Florida including the Tampa area, with a second landfall possible as Wednesday or Thursday.

Organizers of next week's Republican National Convention in Tampa say they are monitoring the storm. Some 70,000 delegates, journalists and protesters are expected, and Florida Gov. Rick Scott said there are no plans to cancel the convention.

A hurricane warning is in effect for the Florida Keys including the Dry Tortugas; the west coast of Florida from Bonita Beach southward to Ocean Reef, and Florida Bay.

A hurricane watch is in effect for Florida's east coast from Golden Beach southward to Ocean Reef, Andros Island in the Bahamas and Haiti. A hurricane watch means that hurricane conditions are possible within the watch area within the next 24 to 36 hours.

The tropical storm warning has been extended northward along Florida's east coast to Sebastian Inlet. Tropical storm watches have been issued along Florida's east coast north of Sebastian Inlet to Flagler Beach, and for Florida's west coast, north of Bonita Beach to Tarpon Springs.

Tropical Storm Isaac swept across Haiti's southern peninsula early Saturday, bringing flooding and at least three deaths while adding to the misery of a poor nation still trying to recover from the terrible 2010 earthquake. At least three people were reported dead.

The tropical storm watch for Jamaica has been discontinued.

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