Officials in North Carolina have already issued mandatory evacuation orders for coastal Dare County and Hatteras Island. Trump said the hurricane was "one of the worst storms to hit the East Coast in many years". "We're liable to have a whole lot of flooding".
North Carolina should brace for three dangers from Florence, Cooper said: coastal ocean surges, strong winds and flooding.
Classified as a Category 4 on the five-step Saffir-Simpson scale of hurricane strength, Florence was the most severe storm to threaten the US mainland this year and the first of its magnitude to target the Carolinas since 1989, when Hurricane Hugo barrelled over Charleston, South Carolina.
Hurricane-force winds are extending up to 65 kilometres from the storm's centre, while tropical-storm-force winds are blowing out at up to 240 kilometres.
The hurricane center said the storm is expected to strengthen and speed up as it approaches the Carolina coast in the coming days.
In Charleston, South Carolina, people filled sandbags and stocked up on food. "We are going to put everything else away and then we are going to put some concrete blocks in front of the doors just so rushing water and wind can't blow the doors back in", said Matthew Littleton with Casper's Marina.
Florence will hit the mid-Atlantic states later in the week. "This is probably the only exercise I get this week".
As a result, Florence "is expected to be an extremely risky major hurricane through Thursday", Sept. 13, said the NHC.
Arnold also shot the image below of Florence from directly above the storm.
Evacuations were also ordered along the Virginia coast for about 245,000 people, according to Gov. Ralph Northam.
In Virginia, home to the world's largest sea base, the USA navy has ordered all ships to sea in preparation for the storm, where they can more safely ride out the violent wind and waves.
A tropical storm warning is in effect for Maui County and Hawaii County and a tropical storm watch is in effect for Oahu. "The potential there for catastrophic consequences definitely exists", said Dennis Feltgen, a meteorologist and spokesperson with National Oceanic and Atmospheric Administration's National Hurricane Center (NHC).
North Carolina Governor Roy Cooper told a news conference his state was in "the bull's eye".
RAINFALL: Olivia is expected to produce total rainfall accumulations of 10 to 15 inches. "So we don't want anyone comparing storms".
Quagliariello advised the public to consider the path's "cone of uncertainty", which shows where the hurricane is likely to go two-thirds of the time. "With Florence strengthening into a hurricane this morning and continuing to move west, Florida families need to remain alert and remember that storms like this can change course and strengthen at any moment", said Gov. Rick Scott.
Hurricane conditions may arrive by late Thursday or Thursday night. Arnold shared his first photos of Hurricane Florence, taken when it was still a Category 2 storm. There is the chance that Isaac will strike Puerto Rico - still recovering from the deadly Hurricane Maria last September - as a tropical storm.