All Broadway performances were preemptively shut down for the weekend in advance of Hurricane Irene’s arrival in Gotham Saturday night.By Saturday morning, many Off Broadway productions had announced they would shutter for the weekend as well. All activities related to Off Off Broadway’s New York Intl. Fringe Festival also were scuttled for both Saturday and Sunday. Although industry types had initially put on a brave face and expected to soldier on despite the weather, legiters seemed to sit up and take notice when it was announced Friday that Gotham’s Metropolitan Transportation Authority would suspend mass transit beginning at noon on Saturday. With public transportation such as subways, buses and commuter trains definitively out of the picture, it looked certain that most ticketholders — not to mention Main Stem casts and crews — would face insurmountable obstacles in getting to theaters, even if the weather proved less severe than expected. Move is a rare emergency cancellation for the Rialto, which almost never misses a perf due to extreme weather conditions such as blizzards. The last emergency-related darkening happened over the two days following the Sept. 11 attacks in 2001, and perfs also were nixed due to a citywide blackout in 2003. Labor strikes halted shows for multiple perfs in 2003 and 2007. Most productions on Broadway would have played three or four performances over the two darkened days. With sales always heaviest over weekend slots, the cancellations are sure to take a significant bite out of weekly grosses across the board.