ATLANTA (AP) — Hurricane Florence has strengthened into a Category 3 storm with 115 mph (185 kph) maximum-sustained winds as it swirls toward the U.S. East Coast.

Forecasters at the National Hurricane Center say Florence is expected to be an extremely dangerous storm by the time it nears the coast of South Carolina or North Carolina on Thursday.

As of 11 a.m. EDT, Florence was centered about 580 miles (935 kilometers) south-southeast of Bermuda, moving west at 13 mph (20 kph).

Far behind Florence is Hurricane Isaac, which had maximum sustained winds at 75 mph (120 kph). Isaac was centered about 1,150 miles (1,855 kilometers) east of the Windward Islands and moving west at 14 mph (22 kph).

The hurricane center says Isaac is a very small hurricane and its intensity could fluctuate as it approaches the Caribbean.

However it’s still expected to be at or near hurricane strength by the time it reaches the Lesser Antilles.

Forecasters said Hurricane Helene was strengthening far from land over the open Atlantic, centered about 375 miles (600 kilometers) west of the southernmost Cabo Verde Islands.

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