At 0900 GMT, Isabel's center was 1,065 kilometers (660 miles) south-southeast of Cape Hatteras, North Carolina, or about 700 kilometersmiles) east of Nassau, the Bahamas, the National Hurricane Center (NHC) said.

The storm "has become less organized during the past several hours," packing maximum sustained winds that have decreased to nearly 185 kilometers (115 miles) per hour with higher gusts, the center said.

Little change in strength was forecast during the next 24 hours, it added.

Isabel dropped overnight to a category-three storm on the Saffir-Simpson scale and was moving toward the northwest near 11 kilometers (seven miles) per hour.

"Large ocean swells and dangerous surf conditions are already being experienced along portions of the US southeast and mid-Atlantic coasts," the center warned, adding that the same conditions would also prevail "over portions of the Turks and Caicos Islands... and the islands of the Bahamas."

A hurricane watch was expected to be issued late Tuesday for portions of the mid-Atlantic coast, the center said, adding that Isabel was threatening the US coastline "from the Carolinas northward to southern New England."

If it keeps its current direction, the hurricane is expected to make landfall within 36 to 72 hours.

Experts say landfall might occur anywhere over a wide stretch of the US east coast, from the southern state of Georgia to the New England region, north of New York.

Even without hitting the shoreline, Isabel will still bring high winds, rain, and dangerous surf and riptides to the US coast.

"That is a virtual guarantee," said Eric Blake of the Miami-based center. "Even if it missed you by 100 miles, you will still feel its effects."

TERRA.WIRE