The 2018 hurricane season blew into high gear on Sunday.
In its 11 p.m. Sunday advisory, the National Hurricane Center upgraded Tropical Storm Isaac to a Category 1 hurricane, with winds of nearly 75 mph.
Isaac became the fifth hurricane of the 2018 Atlantic Season and the third storm being actively tracked in a busy weather weekend.
But the gravest threat to the U.S. remains Hurricane Florence, which is expected to strengthen considerably by Monday night and remain "an extremely dangerous major hurricane" through Thursday, according to the Hurricane Center.
Florence continued its west-northwest crawl toward the southeastern U.S. coast, packing maximum sustained winds of 90 mph.
The center of the hurricane is predicted to move over the southwestern Atlantic Ocean between Bermuda and the Bahamas by Wednesday and could intensify into a Category 4 storm, with winds reaching 130-156 mph, before it makes U.S. landfall sometime Thursday or early Friday.
Forecasters said it was too soon to determine the exact timing, location and magnitude of storm surges and flooding Florence will cause.