The film, officially titled "Sharknado 2: The Second One," nearly tripled the 1.37 million viewers who saw last summer's premiere of the original "Sharknado" film.
Meanwhile, Nielsen estimates that 5.5 million people saw one or more of the 581,000 tweets posted during the airing. At one point, the film held all top 10 trending topics in the United States. By comparison, 318,000 tweets about the first "Sharknado" film were posted when it premiered last July.
In campy fashion, "Sharknado 2" moved the action from Los Angeles to New York City, which was besieged by its own fearsome storm of rain and falling sharks.
Syfy said the film will air again Saturday and Sunday.