MIAMI - Hurricane Isabel's sustained winds increased to 160 mph yesterday as the Category 5 hurricane swirled ominously closer to the East Coast.

The hurricane had been lowered to a Category 4 storm after its sustained winds fell to 150 mph, but it was reclassified after a hurricane hunter plane flew into the eye to measure its intensity yesterday afternoon. A hurricane hits the top of the Saffir-Simpson hurricane scale when its winds reach 156 mph.

The slow-moving, powerful storm was still several days from land, and forecasters were unsure whether it would strike the United States. However, computer models predicted that it would turn toward the Carolinas over the next five days.

"It's not definite, but things are looking more ominous than [Friday] for the East Coast," National Hurricane Center meteorologist Eric Blake said yesterday.

At 5 p.m., Isabel was centered about 375 miles northeast of San Juan, Puerto Rico, and moving west-northwest at 12 mph. Forecasters expected it to continue that movement until this afternoon.

The National Hurricane Center's five-day forecast for Isabel puts the hurricane roughly 200 miles east of the North Carolina-South Carolina border early Thursday, if it makes a predicted turn to the northwest.

Forecasters said Hurricane Isabel could still strike anywhere from north Florida through the mid-Atlantic, and officials warned East Coast residents to be alert. They expected to know more about the potential direction of the storm tonight.

Some residents along the East Coast were buying water, plywood and other supplies just in case Isabel made landfall.

In coastal Georgia, the Chatham County Emergency Management Agency encouraged people to review their hurricane plans, which should include adequate supplies, updated insurance coverage and evacuation routes.

South Carolina Gov. Mark Sanford and other state officials were briefed yesterday by the state Emergency Management Division on emergency preparations. The state went on an elevated alert status Friday.

The last Atlantic hurricane to develop into a Category 5 storm was Mitch in 1998, which killed about 11,000 people in Central America.

The last two Category 5 hurricanes to strike the U.S. coast were Andrew in 1992 and Camille in 1969. Andrew, still the most expensive natural disaster in U.S. history with a $30 billion damage toll, tore through south Florida and Louisiana, killing 43 people. Camille killed 143 on the Gulf Coast and 113 in Virginia flooding.