Metrolinx is warning GO Transit customers to brace for change as it gets set to close Union Station's busy Bay Street Concourse for two years of renovations.

The terminal will close on August 16, with all GO Transit riders being re-routed through the recently redeveloped York concourse. GO Transit staff will be stationed outside the downtown hub to guide commuters through the changes once they take place.

"It's a big change for commuters," said Metrolinx spokeswoman Anne Marie Aikins.

"You want your commute to be forgettable," she said, adding that for a little while, at least, the changes may be "uncomfortable."

In addition to the route change, commuters will also have fewer options when it comes to grabbing a snack or coffee, as the York concourse doesn't have any vendors at this time.

Aitkins said businesses will begin opening gradually in the fall and Metrolinx is hoping to open some coffee kiosks in the meantime. The outdoor market on Front Street, set up for the Pan Am and Parapan Am Games, will also remain open until the end of September.

The eventual payoff, Aikins said, will be a far larger and more airy Bay concourse with almost triple the amount of space to wait for trains.

"It'll be worth the wait, I promise you," she said.