The panicles of flowers are a little reminiscent of horse chestnut flowers. In Catalpa each flower is much larger and the whole panicle is not as neatly-shaped.
This example is on Albany Road in Chorlton. I took all these photos today in a light rain under a lead-grey sky. I had not noticed they were in flower soon enough to plan to take my camera out during the recent heatwave. At least I did not have to cope with the glare of the bright white flowers overwhelming the camera's optics.
Catalpa bignonioides flowers.