The system swept through the Dominican Republic late on Thursday with similarly devastating effects and by Friday afternoon generated maximum sustained winds near 75 mph, passing the 74 mph threshold to be classified as a hurricane.
From Friday night through to Monday South Florida and east-Central Florida could expect between two to four inches of rain, with isolated maximum totals of six inches.
"There is a risk of impacts from winds, heavy rainfall, and storm surge beginning late this weekend along the northeastern Florida coast and spreading northward along the remainder of the US east coast through early next week," the National Hurricane Centre (NHC) said.
"Interests along the entire US east coast should monitor the progress of Isaias and updates to the forecast."
The NHC has issued a hurricane watch for portions of the Florida east coast, warning that hurricane conditions could are possible within the area. Large areas of the Bahamas are under a hurricane warning as of Friday morning.
Goverrnor Ron DeSantis said “Florida is fully prepared for this and any future storm during this hurricane season”, adding that there are stockpiles of personal protective equipment, generators, bottled water, and meals ready to be distributed.
Officials in the state have made moves to close beaches, marinas, and parks in Miami-Dade County as of Friday and the county has prepared 20 evacuation centres on standby that could be set up with Covid-19 safety measures.
The hurricane forecast comes at one of the worst possible times for the state as it continues to see a large rise in fatalities from Covid-19 after a surge in infections through June and July.
2 PM EDT 7/31: Isaias getting better organized as tropical storm conditions and heavy rains spread into the Central Bahamas. Radar imagery from Bahamas. More info: https://t.co/tW4KeGdBFb #hurricaneIsaias pic.twitter.com/1lYIrxUzzm
— National Hurricane Center (@NHC_Atlantic)
Fears of the unknown extent of the impact the unpredictable system could cause have forced Florida to close a large amount of its coronavirus testing sites over the weekend.
The Florida Division of Emergency Management announced on Friday that state-supported Covid-19 testing sites will remain open in 11 counties.
“Look, if we have a major hurricane here then we’re going to have to evacuate a number of people and then we’re going to have to ... try to keep them separated as much as possible,” Miami-Dade County Mayor Carlos Giménez told CNN. “That’s a concern.”
“When you’re not testing is also a concern,” Mr Giménez said. “But the greater danger, the immediate danger has to be taken care of first, and that’s getting our people out of harm’s way."
Additional reporting by Associated Press.