The ninth tropical storm of the Atlantic hurricane season, Isaac, formed Friday east of the Windward Islands, prompting the governments of the Barbados and Martinique to issue storm warnings for their islands.

At 9 p.m. EDT, the center of Isaac was near latitude 11.7 north, longitude 57.2 west, or about 190 miles east-southeast of Barbados. It was moving west-northwest near 15 mph and was expected to continue that motion through Saturday.Maximum sustained winds reported by Air Force reconnaissance planes were 40 mph, with higher gusts in squalls. Forecasters at the National Hurricane Center in Miami said conditions favored slow strengthening by Saturday evening.