Subtropical storm Alberto formed over the northwestern Caribbean Sea, the US National Hurricane Center (NHC) said in an advisory on Friday. The system is located about 90km (55 miles) south of Cozumel, Mexico, packing maximum sustained winds of 65kph, according to the Miami-based weather forecaster. “Heavy rainfall expected to affect the Yucatan peninsula, western Cuba, Florida and the northeastern Gulf Coast through the weekend,” the NHC said. Alberto is the first storm of the Atlantic hurricane season, which officially starts June 1.