Meteorologists warn the storm may be one of the worst to hit the region in decades and could potentially be the worst to hit ever. "Inland flooding kills a lot of people, unfortunately, and that's what we're about to see", he said.
Airlines and hotels may waive change fees or cancellation fees for those affected by the storm. Before, the National Hurricane Center feared that Florence would make landfall as a Category 4 storm.
Steering currents - around clear-weather high-pressure systems and stormy low-pressure systems - redirect hurricanes, with the clear-weather systems acting as walls that storms have to go around. Water causes the most deaths during tropical storms and hurricanes, and Florence expected to cause unsafe flooding.
Hurricane Florence could flood thousands of buildings.
Florence's winds and rains began to batter the Carolinas on Thursday.
Winds and rain were arriving later in SC, and a few people were still walking on the sand at Myrtle Beach while North Carolina was getting pounded.
As of 11 p.m., Florence was centered about 85 miles (135 kilometers) east-southeast of Wilmington, its forward movement slowed to 5 mph (7 kph). Some 3,000 people died in the aftermath of that storm.
"Hurricane Florence was uninvited but she's just about here anyway", he said at a news conference. "Today the threat becomes a reality", he said.
"This is a very unsafe storm", said FEMA's Long, urging people still in evacuation zones to heed orders to flee to safer ground. The storm is expected to turn west and then north moving through the Carolinas and the Ohio Valley by Monday, the NHC said early on Saturday.
Antonio Ramirez, a construction worker from El Salvador living in Leland, North Carolina, said he planned to ride out the storm with his dog Canelo.
The Coast Guard said ocean-going vessels were told to prepare to leave.
"This rainfall will produce catastrophic flash flooding and prolonged, significant river flooding", the hurricane centre said. The damage is much more widespread-and while Florence's main targets appear to be the Carolinas, the storm could bring flooding to parts of Georgia and Virginia as well.
While the storm has since weakened, a storm surge of more than 12-feet and almost 30-inches of rain is still expected.
McMaster also said there may be water coming from rivers from North and SC, which could lead to flooding.
It is expected that the hurricane moves on or near the coastline during the night of Thursday through Friday.
However, forecasters warned that the enormous wind field has been growing larger, raising the risk of the ocean surging on to land.
A powerful high-pressure ridge is expected to keep Florence south through the weekend after its expected landfall Friday morning in the Myrtle Beach/Wilmington areas of South and North Carolina. The storm is moving northwest at 17 miles per hour (27 kph).
Hurricane Florence is expected to pack a potentially life-threatening punch as it continues its path toward the United States east coast. "Please heed the warnings", Mr Brock said: "Your time is running out".
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