Humberto, churning far off land, has become the first hurricane of the season in the eastern Atlantic, US forecasters said Wednesday.

Some additional strengthening of the Category 1 storm is possible through Thursday, after which Humberto should start to weaken, according to the National Hurricane Center, located in Miami.

The storm is spinning about 340 miles (550 kilometers) west of the Cape Verde Islands, with maximum sustained winds of 80 mph, according to the center's 1500 GMT advisory.

No coastal watches or warnings are in effect for the system moving north at 9 mph.

Hurricane season lasts from the beginning of June through November.

The National Oceanic and Atmospheric Administration predicted 13 to 19 named storms this season, up from the seasonal average of 12.