Hurricane Isabel weakened on Tuesday as it approached the East Coast of the United States. With winds of about 160 kilometers an hour, forecasters say Isabel could strengthen on Wednesday as it passes over the warm waters of the Gulf Stream just off the U.S. East Coast. A hurricane watch is in effect for the U.S. states of North Carolina and Virginia.

Forecasters say hurricane force winds will begin affecting the states of North Carolina and Virginia by late Wednesday. Stacey Stewart, a hurricane specialist at the National Hurricane Center in Miami, says a high-pressure weather system just off the East Coast of the United States will block Isabel from moving North and push it ashore.

"We do expect a hurricane landfall somewhere in the general vicinity of North Carolina, and certainly we could not rule out a lightly farther north landfall, but it does look like the East Coast of the United States is going to get hit by this hurricane," he said.

U.S. military authorities have moved ships out to sea from Naval bases to ride out the storm and military and other aircraft have been moved inland as Isabel approaches.

Local authorities in the states of Virginia and North Carolina are urging residents of coastal areas to secure their properties and evacuate. Forecasters and emergency authorities say their main concerns are focused on storm surges that could be higher than 6 meters. Forecaster Stacey Stewart at the National Hurricane Center says storms like Isabel can take a great deal of time to pass through an area.

"Because the storm is so large a lot of these effects are going to be occurring maybe two or three times as a result of the tidal fluctuations," he said. "So you will get a little bit of a surge, maybe five feet (1.5 meters) coming in at high tide, and then a higher surge say 10 feet (3 meters) coming in low tide. There will not be much of a change in the actual water level. And then they might get a higher surge of 15 feet coming in at high tide, and then they will see a very sudden rise in the ocean surface. So people need to be aware that this is going to be a long-lasting storm. It is not just going to come in and go out in just a few hours."

Forecasters say even areas not affected by Isabel's hurricane force winds will be hard hit by heavy rains and there could be heavy flooding across the mid-Atlantic region of the U.S. East Coast.

Even though Isabel has weakened, it is still considered a major hurricane and one of the strongest to affect the U.S. East Coast in several years.

September is usually the most active month in the six-month Atlantic and Caribbean hurricane season that ends on November 30.