Isaac strengthened Friday into a hurricane in the open waters of the Atlantic Ocean and could cause dangerous waves in parts of Bermuda while Tropical Storm Joyce formed and wasn’t threatening land, forecasters said. Isaac was about about 980 miles (1,577 kilometers) east-northeast of Bermuda and about 1,175 miles (1,890 km) west of the Azores, with maximum sustained winds of 75 mph (121 kph). It was heading east at 12 mph (19 kph). There were no coastal watches or warnings in effect for either storm, but the waves from Isaac could cause life-threatening surf and rip current conditions in Bermuda, the Miami-based U.S. National Hurricane Center said. Potentially dangerous waves also could spread to the Azores, the center said. Isaac is expected to strengthen before gradually weakening by the end of the weekend. The storm was churning in the ocean as Hurricane Helene made landfall in northwestern Florida as a Category 4 storm before weaking early Friday, leaving behind flooding, damage and power outages. Also Friday, Joyce became a tropical storm. It’s located about 1,325 miles (2,130 km) east of the northern Leeward Islands and has maximum sustained winds of 40 mph (65 kph). It was moving northwest at about 13 mph (20 kph). The storm was expected to strengthen gradually through Sunday before weakening early next week.