The fourth tropical storm of the 2006 hurricane season, Debby, formed off the coast of Cape Verde in the eastern Atlantic Tuesday, U.S. forecasters said in Miami.

The depression that formed Monday was centred 480 kilometres west of the southernmost Cape Verde islands and was moving toward the west-northwest at speeds of near 30 km/h, the National Hurricane Center said.

The storm had maximum sustained winds near 105 km/h, with some strengthening forecast for the next 24 hours.

Cape Verde is about 560 kilometres off the African coast.

Long-range forecasts show the storm nearing Bermuda in about a week. But it was still too early to tell if it would hit land, senior hurricane specialist James Franklin said.

It is the fourth named storm of the 2006 Atlantic hurricane season.