Hurricane Irene weakened from an expected Category 2 or Category 3 storm to Category 1 before hitting the North Carolina coast this morning.
Click HERE to download graphic: Irene's Path (116.32kB)
The National Hurricane Centre in Miami said sustained winds of 80mph were recorded near Jacksonville with gusts of up to 94mph at the storm's leading edge.
Irene caused relatively little damage strafing the Bahamas and other Caribbean islands, but the fierce storm was threatening to pound a far larger area this weekend, extending north over the densely populated metropolitan areas of Washington DC, Philadelphia, New York and possibly Boston.
For many in those cities, Irene represented an unfamiliar threat. While most New Yorkers know that their city is potentially vulnerable, in the last 200 years it has been hit by only a handful of significant hurricanes. Very few remember the storm of 1938, dubbed the Long Island Expressway, that barrelled into the city and neighbouring states, killing 600 people, with serious flooding and 17ft storm surges.
In September 1821, a hurricane raised tides in New York Harbour by 13ft in just an hour and inundated the southern tip of Manhattan, including the areas that now include Wall Street and the new World Trade Centre memorial.
"One of my greatest nightmares was having a major hurricane go up the whole north-east coast," Max Mayfield, the National Hurricane Centre's retired director, told the Associated Press. "This is going to be a real challenge... there's going to be millions of people affected."
President Barack Obama warned Americans to obey orders to evacuate from the path of what is likely to be an "extremely dangerous and costly" storm. "All indications point to this being a historic hurricane," he said in a statement to reporters from the farm where he is vacationing on an island off the Massachusetts coast.
"I cannot stress this highly enough, if you are in the projected path of this hurricane you have to take precautions now," Mr Obama said.
States of emergency were in effect in multiple eastern states last night, including New Jersey, Maryland and Connecticut. In New York, Mayor Michael Bloomberg ordered the evacuation beginning at 8am yesterday of hospitals and seniors' care homes in lower-lying areas of the city, including Coney Island in Brooklyn.
He also called for the evacuation of parts of the Financial District of Lower Manhattan and coastal areas of the outer boroughs. The order affects 250,000 people the Mayor wants out of their homes by 5pm today, to protect them from floods that might be caused by a storm surge. Officials warned that a general-population evacuation order for those areas could come this morning. The city's public transport system, including the subway, will also be shut down completely today.
While the storm had weakened a little early yesterday there were concerns that it could strengthen again before making landfall. Forecasters were warning that the dangers from Irene were intensified because it was moving unusually slowly and covered an extremely wide area, increasing the threat not just of wind damage but also of serious and widespread flooding, extending inland by 100 miles or more.
For certain, the most populous area of the US could expect at least 48 hours of travel chaos. In New York there were concerns that much of the subway system might be flooded, while all the city's airports were threatened because they lie on or close to the water.
Only when the mopping up begins on Monday and the storm heads into eastern Canada will the full extent of the hurricane's effect become clear. But there were fears that Irene could cause billions in damage in 48 hours.
Additional reporting by Independent staff.Reuse content