I don’t have time to make something but I’ve done it before doing this. Here are the basics:
1) make a comp 5 seconds add a video swish pan if you have it. Loop it. So you have a g=fast moving blurry image / images moving from one side of the screen to the other. Or create an animation of lights, letter, and thing flying across the screen left to right.
2)Add or turn on motion blur.
3)Make a new comp and place the first comp in it.
4)Add Effect : Mesh warp. Distort to the shape of tornado. Set keyframes.
5) move down timeline 2 seconds move all the distortion markers so the tornado has some life.
6) repeat step 5.
7) there’s your tornado. Now just tweak to taste and place comp over your footage.
Ideas: double it up comp and offset the time and color. try different transfer modes. Add a slight shake to the entire thing(position / scale keyframe).
Let me know if this makes no sense or you need any help.