The hurricane's winds will likely continue to fluctuate.
"Isabel could still be a major hurricane at landfall," according to a statement released by the National Hurricane Center (NHC). Major hurricanes are those with sustained winds of at least 111 mph. That view did not change during the day, even as the storm weakened.
Forecasters stressed that the storm's expected path remains highly uncertain.
"Interests from the Carolinas through the northeastern states should closely monitor the progress of Isabel," said NHC forecaster Jack Bevin.
At 5 p.m. ET, the hurricane was 740 miles south-southeast of Cape Hatteras, North Carolina and on an apparent course to strike there. It was 470 miles east of Nassau in the Bahamas, moving northwest across the Atlantic at about 8 mph. It had been scooting along at 12 mph over the weekend.
The best estimate by the NHC has Isabel coming ashore along the Outer Banks of North Carolina sometime Thursday and tracking inland through Virginia and Pennsylvania.
"A small change in direction could result in a landfall well to the north of the mid-Atlantic coast," Bevin said. New York City and other major metropolitan areas in the Northeast could be targets.
For now, Florida and its Space Coast are not expected to be severely impacted by the storm. However, forecasters say, hurricanes cannot be discounted until they've moved north of a particular location.
Isabel is following a classic path around the southern and western fringes of the Bermuda high-pressure system, which typically dominates the air over the mid-Atlantic this time of year.
There is always a chance that a storm on Isabel's general path will curve out to sea. Forecasters do not expect Isabel to do so, however.
Exactly when Isabel comes ashore, if it does, depends in part on its forward speed, which can increase dramatically as the storm moves farther north. Hurricanes frequently speed up to 15 mph or more as the approach the Carolinas. In extreme cases, they can race along at more than 50 mph, scientists say, if they stay over the ocean and head toward the Northeast under the right conditions.
Depending on how quickly Isabel moves north, the Bermuda high and other weather factors west of the storm could squirt the hurricane farther north than currently expected, forecasters said.
Meanwhile, the NHC is also struggling to predict how strong Isabel will be when it hits land. It is normal for a hurricane to fluctuate in intensity as ocean water temperatures and atmospheric conditions vary. NHC forecasters expect Isabel to maintain roughly its present strength through landfall.
Not since Andrew devastated parts of Florida in 1992 has a Category 5 storm come ashore in the United States. Hugo in 1989, at Category 4, was the second costliest storm ever, behind Andrew. Hugo inundated coastal regions of South Carolina. The only other Category 5 storms recorded making landfall were Camille in 1969 and an unnamed storm in 1935.
The last Category 5 storm in open water was Mitch, in 1995. It weakened before coming ashore but still killed 11,000 people in Central America.
As with all hurricanes, Isabel is a broad region of low atmospheric pressure. Its winds blow counterclockwise as viewed from above.
Pressure is lowest at the center of the storm, pulling air at the surface inward. This churns the sea into a frenzy of waves and spray, feeding ocean water into the storm that rises and becomes rain. The air rushes upward near the storm's center and flows out the top as if from a chimney, allowing more air at the surface to race to the storm center.
Large waves and dangerous swells, pushed ahead by Isabel, are aleady arriving along the East Coast.
Residents from the Carolinas northward are encouraged to take stock of their situation.
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"Isabel is a good reminder that Americans in coastal regions should take the time to prepare for a hurricane well before it arrives by developing a family communication plan, an emergency supply kit and by learning more about the threats hurricanes present," said Michael Brown, Under Secretary for Emergency Preparedness and Response.
Among the recommended preparation steps:
- Set aside several days' worth of bottled water or store tap water in clean containers with lids. For drinking, you need two quarts per person per day.
- Stock several days' supply of canned and/or nonperishable foods that don't require cooking.
- Check batteries and working status of flashlights and a transistor radio.
- Make sure you have a first aid kit.
- Discuss an emergency plan with your family, including how and where to meet or contact one another.
Isabel is the ninth named tropical storm of the Atlantic hurricane season, which began June 1 and ends Nov. 30.
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