Tropical Storm Florence is practically stalled over the Carolinas and the monster storm could dump drenching rains of up to 1 metre.
That, in turn, could trigger epic flooding well inland.
North Carolina Gov. Roy Cooper calls Florence the ``uninvited brute'' that could wipe out entire communities.
The storm is some 645 kilometres wide. Power outages are widespread including over 740,000 in North Carolina and 163,000 in South Carolina. Rescue crews have used boats to reach hundreds besieged by the rising waters.
Early Saturday morning Florence's winds weakened to 100 kph as it moved west northwest of Myrtle Beach, South Carolina.
The intense rain is also expected to cause major river flooding into early next week.
So far, the storm is blamed for at least four deaths.