1:49 Flash

Credit to MSL's tutorial. Throw this flash to get your teammate into pit, the strongest position at A long. Follow it up by holding an off angle at the corner to create a crossfire with your friend in pit.

Start next to this wall at the top of long A:
Stand against the edge, it's OK to be a bit to the left. Not a precise throw. Aim over this sign (on a line up from the cross). Throw a tiny bit after 1:49 on the clock.
This is where it should pop, timed to when the earliest long terrorist can peek.