Wheel vibrates when applyin brake

I have a 2001 Odyssey and when I apply the brake the steering wheel vibrates. When I use the car on the highway for ove 30 minutes and I apply the brake, the steering wheel vibrates much more than if the car was cold. When I first start the car and apply the brakes at low speeds, there is no vibration on the steering wheel. It feels like the discs are warped but I dont understand why it would be worse after I use the car on the highway.

Any help would be appreciated.:banghead:

It does sound like the rotors are warped. They can get worse when they heat up.

cut the rotors (not expensive) and ballance the weels.
easy fix.