A simulation weather video is showing what the life-threatening Hurricane Florence storm surge might look like if it reaches a frightening nine feet (2.7m).

Life-threatening storm surges of up to 13 feet (4m) have been forecast in some areas when the monster storm eventually makes landfall in North and South Carolina.

The Weather Channel's forecast video shows the potential damage such surges could inflict on the southern states.

The video shows Weather Channel presenter Erika Navarro standing in front of a screen showing a suburban street as water rises.

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Yesterday, Dr Greg Postel, the network's hurricane specialist, said three feet (0.9m) of water was enough to knock people off their feet, potentially carry cars away and flood lower levels of buildings.

Six feet (1.8m) of storm surge could carry large objects like cars underwater and leave lower levels structures submerged in water, according to Dr Postel.

The video also gives a frightening indication of what nine feet (2.7m) of water looks like - completely submerging lower buildings.

In addition to the life-threatening storm surge, Florence is also forecast to dump up to 40 inches (1m) of rain after it makes landfall in North and South Carolina Thursday night or Friday.

Florence's winds had dropped from a peak of 225km/h to 169km/h by Thursday, reducing the hurricane from a terrifying Category 4 to a 2.

But forecasters warned that the widening storm - and its likelihood of lingering around the coast for days - will bring life-threatening storm surge and torrential rains.

The simulation has been trending on social media.
The simulation has been trending on social media.

The centre of Florence is expected to hit North Carolina's southern coast Friday, then drift southwest before moving inland on Saturday.

Georgia joined North and South Carolina, Virginia and Maryland in issuing an emergency declaration as forecasts showed Florence dumping historic amounts of rain - potentially 37 trillion litres - on the southern states.

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The storm was already generating 83-foot (25m) waves at sea on Wednesday.

The Weather Channel simulation shows the water level at nine feet.
The Weather Channel simulation shows the water level at nine feet.

Forecasters at the National Hurricane Centre warned that Florence remained deadly because of its size and slow forward speed, even if its top sustained winds have dropped it to Category 2 status as a hurricane.