Florence's flooding is expected to reach far inland, with more than one foot (30 centimeters) expected in some areas.
"But looking back at the forecast tracks for Hurricane Florence from the National Hurricane Center (NHC) and the ensemble members of the leading global forecast models a couple of days ago, what stood out was how relatively straightforward they were", RMS said.
The National Hurricane Center said in its 11 p.m. Thursday update that Florence had weakened to a Category 1 storm.
"We are ready, but this is going to be one of the biggest ones to ever hit our country", said the president. The NHS warned of "catastrophic" flash flooding from rainfall totals as high as 40 inches.
McMaster urged people in areas under Tuesday's mandatory evacuation order to leave now if they haven't already done so. As Florence moved inland, it was expected to pass near-enough to bring winds of up to 40 miles per hour to Charlotte, the second-busiest hub for American Airlines.
The National Hurricane Center's best guess was that Florence's eye would blow ashore as early as Friday afternoon around the North Carolina-South Carolina line.
Tropical storm Florence lumbered inland on Saturday, knocking down trees, flooding rivers, and dumping sheets of rain in the Carolinas where five people have died.
"Hurricane Florence was uninvited but she's just about here anyway", he said at a news conference.
The storm's centre was about 145 miles (235 km) east of Myrtle Beach, South Carolina as of Thursday night. "A slow motion across portions of eastern SC is forecast Friday night through Saturday night".
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After making landfall in the lower Outer Banks of North Carolina, the storm is expected to make a shift to the left toward SC before trekking west and then north.
It is unclear exactly how many people fled, but more than 1.7 million people in the Carolinas and Virginia were warned to clear out.
The Miami-based center says the center of Florence will approach the coasts of North and SC later today.
High tides along the James and York rivers are expected to be as much as 3 feet above normal, which could affect flood-prone areas and roads, the weather service said.
Scientists said it is too soon to say what role, if any, global warming played in the storm.
"The shelters are not taking dogs", Ramirez said.
In addition, the threat of storm surges looms for areas in the path of the storm, meaning life-threatening inundation from rising water moving inland is possible.
Florence was moving west-southwest at about 5 miles per hour (7 km/h), with its centre located over eastern SC.
NOAA's advisory also states that the southeastern and mid-Atlantic states should monitor the progress of Hurricane Florence closely.