The Wilmington airport had a wind gust clocked at 105 miles per hour (169 kph), the highest since Hurricane Helene in 1958.
Hurricane-force winds extended 130km from its centre, and tropical storm-force winds reached out to 315km.
The powerful storm has caused countless trees to collapse, including the one that killed the mother and her son.
The wind howled and sheets of rain splattered against windows of a hotel before dawn in Wilmington, where Sandie Orsa of Wilmington sat in a lobby lit by emergency lights after the power failed.
More trees will come down, more power lines will fall, and the number of power outages will go up, said Ken Graham, director of the National Hurricane Center.
A gust of 169km/h was recorded at Wilmington airport, surpassing the power of Hurricane Fran two decades ago.
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Hundreds more had to be rescued elsewhere from rising waters. The city said two FEMA teams were working on swift-water rescues and more were on the way.
"We've got nearly 20,000 people in 157 shelters", Cooper said.
"There is still time, but not a lot of time", said Derrec Becker of the South Carolina Department of Emergency Management.
U.S. Southeast power companies said almost 440,000 homes and businesses in North Carolina and SC were without power on Friday as Hurricane Florence hit the coast.
Officials said some 1.7 million people in the Carolinas and Virginia were warned to evacuate, but it's unclear how many did. Winds knocked down trees all over.
As Florence raged, a tropical disturbance in the Gulf of Mexico brought heavy rain to already saturated areas along the Texas coast, resulting in street flooding and prompting some schools to cancel or cut short classes.
Officials in several states have declared states of emergency, including in the Carolinas, Georgia, Virginia and Maryland, where coastal areas are still recovering from summer storms.
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Life-threatening storm surge is being reported along the coast of the Carolinas.
Florence had been a Category-3 hurricane on Thursday but dropped to Category-1 before coming ashore.
Top winds were holding at 90 miles per hour - that's just a Category 1 hurricane - but some communities were already submerged in more than six feet of water as the storm drenched the coast.
At time of writing, Hurricane Florence is inching towards the coastline, and the combination of intense rainfall and gnarly swell threaten to engulf low-lying land in the region.
Not everyone was taking Florence too seriously: About two dozen locals gathered Thursday night in the U.S. behind the boarded-up windows of The Barbary Coast bar as Florence blew into Wilmington. And others could only hope someone would come for them.
"This is our only home".
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Met Éireann said: "Current indications are that (ex-) tropical storm Helene will approach Ireland's south coast during Tuesday". On the forecast track, Isaac will move over the eastern and central Caribbean Sea during the next few days.