MIAMI (Reuters) - Tropical Storm Melissa formed in the Atlantic Ocean on Saturday but posed no immediate threat to land, while Tropical Depression Karen weakened, the National Hurricane Center said.

As of 11 a.m. EDT, Melissa was about 300 miles

west of the Cape Verde Islands, moving northwest at eight miles per hour (13 kilometers per hour) with winds of 40 mph, the hurricane center said.

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"Little change in strength is forecast during the next 24 hours," the center's advisory said.

Meanwhile Karen was weakening, and could degenerate into a low pressure area within 24 hours, the hurricane center said.

Karen's center was about 530 miles east of the Leeward Islands, moving northwest at 9 mph, with winds diminishing to 35 mph, it said.

The 2007 Atlantic storm season, which runs through November 30, so far has produced four hurricanes, including Lorenzo which crashed into Mexico's Gulf coast on Friday and killed three people.