By late Wednesday night, the Category 1 storm - the second hurricane of the Atlantic season - was about 1165 miles east of the Leeward Islands, spinning to the north-northwest at 20 mph.

Additional strengthening is forecast during the next 48 hours and Katia could become a major hurricane by the weekend, the hurricane center said.

The extended forecast map shows the storm passing north of the Caribbean.

Elsewhere, forecasters saw the potential for a new tropical storm that could hit the US Gulf Coast over the weekend.

A cluster of storms over the southeastern Gulf of Mexico could become a tropical depression by Thursday with the help of upper-level winds that are forecast to aid development, the National Hurricane Center said.