DANIELLA LEVINE CAVA, the mayor of Miami-Dade County in Florida, approaches the microphone. “It’s that time of year,” she says, smiling knowingly. She could have been referring to the end of the school year, the beginning of America’s general-election campaign or the premiere of the new season of “The Kardashians”. In fact, Ms Levine Cava was talking about hurricane season, which begins on June 1st, and is expected to be the most active one America has ever experienced.