At 23:00 Thursday local time (03:00 GMT Friday) the hurricane was still off the Florida coast, centred about 37 miles (60km) east of West Palm Beach and was moving north-west at about 20km/h, the National Hurricane Center said.
The hurricane has again been upgraded to a Category Four storm, the second highest hurricane classification, as it heads for the US state of Florida.
The death toll in Haiti as a result of Hurricane Matthew – the most powerful Caribbean storm in a decade – has soared to more than 300, officials say.
Some 50 people were reported killed in the town of Roche-a-Bateau alone.
The nearby city of Jeremie saw 80% of its buildings levelled. In Sud province 30,000 homes were destroyed.
