With winds of 185 kilometers an hour, Hurricane Isabel has strengthened into the second major hurricane of the 2003 Atlantic and Caribbean hurricane season.
Hurricane Isabel is still far out at sea, about 2,000 kilometers east of the Leeward Islands, but forecasters say the storm is strengthening, and could pose a serious threat to Puerto Rico, Hispaniola and Cuba by the end of this week.
The storm is moving over very warm water and has a well-defined core and strong outflow. Forecasters say storms like Isabel can quickly become dangerous, with winds in excess of 240 kilometers an hour.
Forecasters also say Hurricane Isabel seems to be following the path of Hurricane Fabian that pounded the island chain of Bermuda several days ago, leaving at least four dead.
Thousands of homes in Bermuda remain without power and local authorities say Fabian caused millions of dollars worth of damage especially to Bermuda's famous golf courses.
September is usually the most active month in the six month Atlantic and Caribbean Hurricane season that ends on November 30.