Tropical Storm Lisa strengthens as Karl weakens into depression in Atlantic

MIAMI, Sept. 21 (UPI) -- Tropical Storm Lisa strengthened as Karl weakened into a tropical depression Wednesday in the Atlantic Ocean.

Overnight, Lisa slightly intensified as it was 550 miles west-northwest of the Cape Verde islands and traveling 9 mph with maximum sustained winds of 50 mph, according to the National Hurricane Center.

The center said further strengthening is possible Wednesday but it is expected to weaken by Thursday. The "center is not easy to locate and the initial motion is rather uncertain," the hurricane center said.

Over five days, the storm is projected to go west-northwest.

The storm is not expected to affect the United States and will remain over the open waters of the Atlantic, according to AccuWeather. But it noted it could disrupt freighters in this area of the Atlantic.

Karl, which is west of Lisa, weakened overnight to a tropical depression and its "structure is very difficult to determine this morning," the center said. Winds slowed to 35 mph as Karl was traveling 14 mph and was about 350 miles northeast of the Leeward Islands.

Karl is forecast to slightly strengthen and travel in a more northwestern direction through Thursday, the center said.

Although 12 storms have formed this season, just one major hurricane formed – Category 3 Gaston, which had no impact on land.

"Most of the storms this year have been pieces of junk," Phil Klotzbach, a hurricane researcher with Colorado State University, told The Palm Beach Post.