Brief Explanation
When you spin the bottle while holding it upside down it will create a vortex that would allow the air to travel upward through the vortex and the water would travel downward moving faster then when it is dumped out regularly.
Tornadoes are usually caused by heated air, usually over land, but at times beginning over warm bodies of water and moving on to land masses. The warm surface air may be trapped under a localized, colder, higher-atmospheric body of cold air. Cold air is much heavier than warm air, so that situation in itself can be physically unstable. You may observe a heavy, dense cloud structure layered over "normal" clear sky in the distance. The cloud structure begins to lean, or become unbalanced. The "line “or contact zone between the heavy cloud cover and the clear air below it observably begins to tilt, or slant toward earth. The physics involved in a tornado would obviously have to have the force of the wind acting on anything in the path of the tornado. You may also use equations such as the formula for angular momentum:
MOMENT OF ANGULAR
INERTIA x VELOCITY
Physics Behind Tornadoes
Materials
Two, 2 liter bottles
Cello tape
Scissors
Food Coloring
Procedure
1. First, fill one of the two liter bottles 3/4 of the way up.
2. Next, make a neat round hole in two bottle lids with the scissors.
3. Tape the lids back to back with the cello tape.
4. Screw the lids onto the two liter bottles so that they are connected to each other.
5. Invert the bottles and swirl the top of the bottle until it turns into a tornado.
6. Watch as it makes a deep cone and fall below.