Hurricane Irma first formed in the eastern Atlantic as a Category 2 storm and later strengthened to Category 3, just days after the first major hurricane of the season, Harvey, unleashed massive rain and floods over Texas, U.S. officials said Thursday.

Hurricane Irma churned in open waters off the west coast of Africa, packing winds of 100 miles (160 kilometers) per hour, said the Miami-based National Hurricane Center in its 1500 GMT advisory.

"Irma is forecast to become a major hurricane by tonight and is expected to be an extremely dangerous hurricane for the next several days," it said.

The Miami-based weather forecaster later announced that the hurricane was about 720 miles (1,160 km) west of the Cabo Verde islands, packing maximum sustained winds of 115 miles per hour (185 kph).

The storm is currently far from land, but is heading straight toward the southern Caribbean, to the area between the U.S. island territory of Puerto Rico and South America's northern coastline.

Irma is forecast to reach the Lesser Antilles islands in the Caribbean early next week.

South Florida meteorologist Craig Setzer said it was far too early to tell if the storm would impact Florida or the Gulf of Mexico.

Anxiety is running high over the risk of another storm in the southern United States after Harvey pounded the coast of Texas, making landfall Friday as a Category Four hurricane.

Irma gathered strength quickly, rising to hurricane status less than 24 hours after forming as a tropical storm.

No coastal watches or warnings were in effect.