Hurricane Isabel weakened yesterday but tens of thousands of people on the North Carolina coast were urged to evacuate as the storm threatened the eastern US seaboard.
The hurricane was still hundreds of miles out in the Atlantic Ocean but moving steadily on a path that would bring its centre ashore tomorrow on North Carolina's fragile Outer Banks island chain, then north through Virginia and close to Washington DC.
By yesterday evening, Isabel's top winds were 105 mph. It had weakened from a Category 3 to a Category 2 storm on the Saffir-Simpson scale of 1 to 5 that measures hurricanes' destructive power, the National Hurricane Center said.
"I really do have a concern that people are letting their guard down somewhat," center director Mr Max Mayfield told CNN last night. "We can't afford to let that happen. We do think there's another window of opportunity for some strengthening before landfall."
The US Census Bureau said nearly 50 million people could be affected by Isabel's large reach as hurricane-force winds extended up to 160 miles from its centre.
Isabel's first encounter with land could take it over the Outer Banks, a narrow, low-lying North Carolina island chain jutting out into the Atlantic that is a popular vacation spot and home to 55,000 permanent residents.
Officials in Dare County, which includes the central islands, issued a mandatory evacuation order for the 75,000 people in the low-lying county, and closed schools. The governors of North Carolina and Virginia declared states of emergency, enabling them to mobilise workers for the storm and activate the National Guard.
Isabel is the first major hurricane to threaten the mid-Atlantic region since Floyd hit the East Coast in September 1999. Although only a Category 2 storm, Floyd caused massive flooding, killed 56 people and cost $4.5 billion in damage.