Fandango indicated screenings in New York, Boston and Seattle were already sold out Friday ahead of the screening that night, and additional screenings were added at the last minute to meet the demand.
The campy film initially aired July 11 on Syfy and featured sharks in tornadoes attacking and destroying Los Angeles.
A modest 1.4 million tuned into the premiere, but those who watched inundated Twitter with comments and jokes about the film. An encore airing on July 17 brought in 1.9 million viewers and a third showing on July 29 hit a ratings-high 2.1 million viewers, The Hollywood reporter said.
"It's unprecedented for a TV movie to be released in theaters and do this well in limited engagements," Fandango spokesman Harry Medved said, "but then again, cult movies are more fun to watch with a packed audience yelling their favorite lines back at the big screen. You need full audience participation to truly appreciate a film like 'Sharknado.'"
A New York-set "Sharknado" sequel is in the works and is expected to premiere in July 2014.