You can use a dummy unit and give it some meteor model.
When you create the unit, use Animation - set flying height to 1000 at 0. Animation - set flying height to 0 at 333.
The 1000 is the initial height, the 33 is the speed. It will take 1000/333 = 3 seconds to hit the ground. Adjust the values as you see fit. You can start a timer that expires after the calculated time and then kill the unit as it hits the ground.