Katia weakened to a tropical storm in the open Atlantic Ocean on Thursday afternoon, but it could become a hurricane again in the next 12 hours, the National Hurricane Center said. Swells generated by the storm could affect the Lesser Antilles by late Friday.

The maximum sustained winds of Katia, whose center was 930 miles east of the Caribbean's northern Leeward Islands, had decreased to 70 mph shortly before 5 p.m. ET, the hurricane center said. The wind-speed threshold for a Category 1 hurricane is 74 mph.

"Some restrengthening is forecast during the next 48 hours," the hurricane center said in its 5 p.m. advisory.

Katia became a hurricane Wednesday night, with maximum sustained winds of 75 mph.

According to the center's five-day track forecast, the storm could reach hurricane strength again by Friday morning, and could become a major hurricane - with sustained winds at 115 mph - north of the Caribbean Sea next week.

According to the five-day forecast, the storm's center would go north of the Caribbean islands. It's too early to predict whether the storm's center will affect the United States or Bermuda. But the center's advisory said swells generated by Katia "will begin affecting the Lesser Antilles by late Friday."

"These swells are likely to cause life-threatening surf and rip current conditions," the advisory said.