Preparations begin as the Houston Astros honor Jeff Bagwell for...

Preparations begin as the Houston Astros honor Jeff Bagwell for his induction into the National Baseball Hall of Fame at Minute Maid Park on August 5, 2017 in Houston, Texas. Credit: Getty Images / Bob Levey

HOUSTON — The sun shined brightly over downtown Houston on Friday afternoon and the humid air hardly seemed to move. But as workers tended to the playing field at Minute Maid Park — where the Mets and Astros play a doubleheader Saturday — the signs of catastrophe were easy to spot.

At the George R. Brown Convention Center, just down the street from the ballpark, thousands of people displaced by Hurricane Harvey sought services and shelter. Astros players were spotted in the hall, volunteering their time. Mets players also intended to contribute to the relief effort on their day off, though they insisted on doing so away from the public eye. Houston Mayor Sylvester Turner thanked Mets players for meeting with first responders.

Meanwhile, both teams braced for the unknown, which they will face Saturday in Houston’s first major sporting event since the devastation.

“If there’s any positive that comes out of it, maybe people come to the game and get their minds off what’s going on for a few hours,” Jacob deGrom said. “Other than that, I have no clue what to expect.”

September call-ups

The Mets have spent the last five weeks trading veterans for the kind of young arms they hope will help fill out a revamped bullpen for 2018. Two of those new arms — righthanders Jacob Rhame and Jamie Callahan — will join the Mets on Saturday as part of the team’s first wave of September call-ups.

Both sport mid-90s fastballs and will join the bullpen. Rhame, 24, arrived from the Dodgers in a deal for Curtis Granderson. Callahan, 23, came as part of a package from the Red Sox for Addison Reed.

Righties Robert Gsellman and Kevin McGowan are also in line to be recalled once Triple-A Las Vegas ends its season Monday, a source said. The Mets also intend to promote an additional outfielder, though they have yet to decide on the player.

Tim Tebow is not being considered.