(RNN) – Though Hurricane Irma weakened to a Category 3 storm as it moved over Cuba, it regained strength early Sunday morning, once again becoming a Category 4 hurricane.
Irma is located about 40 miles south-southeast of Key West, FL, moving northwest at 8 mph, according to the National Hurricane Center.
The storm has maximum sustained winds of 130 mph.
Late Saturday night, the NHC announced the first hurricane-force wind gusts had been recorded in the Florida Keys.
According to the NHC, Irma is expected to gain more strength before crossing the Florida Keys in the early hours Sunday and hitting the mainland U.S. around 7 a.m.
Florida has already experienced heavy rains and winds, bringing flooding and power loss to residents. Florida Power and Light told the Associated Press it expects millions to lose power.
Almost the entire state of Florida is under a hurricane warning, with life-threatening and historic storm surge likely in parts of south Florida, according to the National Weather Service.
Irma is expected to travel along the southwestern coast of Florida through Monday morning, but portions of Georgia, South Carolina and Alabama are also under advisories, covering everything from hurricane watches to tropical storm watches.
When Irma reaches Florida, it will be the state's strongest hurricane strike since Hurricane Charley made landfall as a Category 4 storm in 2004, according to the Weather Channel.
Hurricane Irma proved catastrophic in the Caribbean, killing 24 people and leaving entire islands, like Barbuda, in ruins.
The NWS warns areas of Florida covered by the hurricane warning could be uninhabitable for weeks or months.