Also in the Atlantic, Hurricane Fabian was losing the characteristics of a tropical storm as it moved over the cold north Atlantic, while a new storm took shape over the warmer eastern tropical Atlantic. The remains of Tropical Storm Henri weakened off the East Coast.
"We are in the peak of the hurricane season, so it is not unusual to have multiple systems out there," said Max Mayfield, director of the National Hurricane Center in Miami.
Isabel strengthened into a major hurricane Monday with maximum sustained wind of 125 mph, making it a category 3 storm, the hurricane center said. It was expected to continue strengthening into Tuesday.
Isabel could reach category four status tonight as it churns west-northwest at 14
At five p.m. Eastern Time, Isabel was about 12-hundred miles east of the northern Leeward Islands in the Eastern Caribbean.
Isabel was forecast to pass north of the Caribbean islands in about four days, but could move farther south and threaten some of them, said meteorologist Eric Blake.
"Right now, it's pretty far away," Blake said. "With our average error being 300 miles, it certainly could be a threat" to the Caribbean.
He said it was too early to say if the storm will threaten the United States.
At 11 a.m. EDT, Isabel was centered about 1,265 miles east of the Leeward Islands in the Lesser Antilles, the chain of Caribbean islands that includes Antigua and Barbuda, Dominica, Martinique, Saint Lucia and Barbados.
Isabel was moving west-northwest at about 14 mph and was expected to continue on that track for at least a day.
Hurricane Fabian was moving toward the north Atlantic after rolling across Bermuda and was located about 680 miles east-northeast of Cape Race, Newfoundland.
Fabian's maximum sustained wind speed was down to about 75 mph, barely strong enough to be ranked as a hurricane, although it was still driving large swells onto the East Coast beaches.
Fabian was expected to lose its tropical characteristics as it moved over cooler water but forecasters said it would remain a large, powerful low-pressure system.
Fabian was the most powerful storm to hit Bermuda in 50 years, knocking out power to thousands of homes and businesses and tearing away roofs. Four people were lost when their cars were blown off a causeway.
Far out in the eastern Atlantic, a new tropical depression formed Monday about 220 miles south-southeast of the Cape Verde Islands, off the coast of Africa. The weather system had maximum sustained wind of about 35 mph, with some strengthening expected by midday Tuesday, and it was moving to the west at only about 3 mph, the hurricane center said.
Tropical depression Henri was moving away from the East Coast after quickly crossing the Florida Peninsula during the weekend.
Henri was about 175 miles south of Cape Hatteras, N.C., and moving northeast near 8 mph. Henri had maximum sustained wind of 35 mph - below the 39 mph minimum threshold to become a tropical storm. Forecasters predicted a slight strengthening into Tuesday but said Henri appeared to be losing tropical characteristics.
The Atlantic Hurricane season began June 1 and ends Nov. 30.