Tropical Storm Katia has strengthened gradually as it moves west-northwest, the U.S. National Hurricane Center (NHC) said on Wednesday. At 05:00 a.m. ET, Katia was located about 985 miles west of the southern Cape Verde Islands, with maximum sustained winds of 65 miles per hour (100 km/h), and was moving west-northwest at 21 miles per hour (33 km/h). "This general motion is expected to continue with a gradual decrease in forward speed during the next couple of days," the NHC said. There are still no coastal watches or warnings in effect, NHC added.