The power grid in the US territory of Puerto Rico was so badly damaged that repairs could take months, authorities on the island said. Irma's core was expected to reach southern Georgia on Monday afternoon before heading to Alabama.
A few hours later, it was downgraded again to Category 2, with maximum sustained wind gusts of 110 mph (175 kph), the National Hurricane Centre reported in Miami.
Jessica Chase, a meteorologist with the National Weather Service in Huntsville said areas of higher elevation, like DeKalb County, will experience strong winds.
- One person was found dead in Orange County in a single-car accident linked to the storm, police said without providing details.
Irma, however, continued to be a threat as it crossed the northern part of the state and because of lingering storm surges along both coasts. Floodwaters have also risen in areas as far as SC including Charleston.
Irma flooded portions of River Street in the tourist magnet city of Savannah, Georgia, and forced police to temporarily shut Highway 80 leading to the barrier island community of Tybee Island.
If the water hadn't pushed out, Shiveley said, storm surge could have been in the eight or nine-foot range.
The islands of the Florida Keys and western parts of the state bore the brunt of the category-four hurricane. Cities as far inland as Atlanta are under a tropical storm watch Monday and Tuesday. Many classrooms also were closed in Georgia, which was was under a tropical storm warning for much of Monday.
Irma, weakened to a tropical depression, is expected to push into Alabama, Mississippi and Tennessee over the next two days.
Meanwhile, a boat that became a coastal SC icon when Hurricane Hugo washed it 2 miles onshore in 1989 now has been relocated by tropical storm Irma.
It cut a devastating track across 10 Caribbean countries and territories, killing at least 28 people there.