The hurricane has moved at only 3-6 miles per hour on Friday, increasing the effect of its torrential rains.
"And it's just a Category 1 hurricane", Tarr said.
At a briefing, North Carolina Gov. Roy Cooper said the risk of fatality will only grow when people venture out once the winds die down. "I made sure ahead of time that we had adequate space for anybody that wanted to try that".
As the storm sat along the edge of the Atlantic, some stretches along the coastal Carolinas received close to 20 inches of rain. Hurricane-force winds extended 80 miles (130 kilometres) from its centre, and tropical-storm-force winds reached out 195 miles (315 kilometres).
Ken Graham, the NHC's director, warned the slow pace of the storm exacerbated its danger even to areas outside its immediate path.
That kind of scenario is likely to repeat itself all over communities in Eastern North Carolina, as swollen rivers flood towns and the pouring rain adds to the misery.
Forecasters said Florence's surge could cover all but a sliver of the Carolina coast under as much as 11 feet of sea water.
Along the coast, floodwaters have been hitting inland towns near rivers that normally discharge into the ocean.
Florence's storm surge and the prospect of 1 to 3½ feet of rain were considered a bigger threat than its winds, which dropped off from an alarming 140 miles per hour earlier in the week.
"The water kept rising and kept rising", he said.
"Rescue workers are working in risky conditions that will only get worse today", he said.
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Officials in SC reported the state's first fatality due to Florence on Saturday.
The No. 1 mission right now, Cooper said, is to save lives.
In nearby New Bern, where water levels reached at least 10 feet overnight, 150 people requested a rescue. Ballance called the rainfall "biblical", saying he's gotten reports from friends that his downtown seafood restaurant was flooded, just like the rest of the small city's historic downtown, and he's anxious about the hundreds of people who needed to be rescued overnight in the city.
As of Friday morning, some 12,000 North Carolinians have gone to stay in shelters as they brace for Florence to make landfall.
In Jacksonville, North Carolina, more than 60 people were evacuated from a hotel after part of the roof collapsed, city officials said. In order to combat any outages, Duke Energy has gotten more than 10,000 of their own employees on standby and requested and received assistance for more than 2,000 workers from other states not being hit by the hurricane. But it was clear that this was really about the water, not the wind.
"This storm has been hovering over us for a while, and we expect it to continue to hover over us", she told the newspaper.
A gust of 169km/h was recorded at Wilmington airport, surpassing the power of Hurricane Fran two decades ago.
More ominously, forecasters said the onslaught on the coast would last for hours and hours because Florence had come nearly to a dead halt at just 3 mph (6 kph) as of midday.
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.
Florence was one of two major storms on Friday.
Forecasters said that given the storm's size and sluggish track, it could cause epic damage akin to what the Houston area saw during Hurricane Harvey just over a year ago, with floodwaters swamping homes and businesses and washing over industrial waste sites and hog-manure ponds.
To prepare for this storm, businesses have been boarding up, and supplies have been readied for what is expected to be a large-scale relief operation.
Meteorologist Ryan Maue of weathermodels.com said Florence could dump a staggering 18 trillion gallons of rain over a week on North Carolina, South Carolinas, Virginia, Georgia, Tennessee, Kentucky and Maryland. Thousands of soldiers from their National Guard forces have been mobilized.