A tornado is rapidly spinning air that develops from a thunderstorms and is on the ground. The ingredients for a tornado are a thunderstorm, winds changing speeds with height and rapidly rising air. When you watch a thunderstorm develop you will notice that the clouds build upward. This rising air is what causes all the rain and hail to form from the water in the air. The addition of changing wind speed and direction with height causes the rising air to spin. Think about spinning a top. You spin your fingers in opposite directions to get the top to spin. This is the same as wind coming from different directions. Most thunderstorms do not produce tornadoes because the spin is not balanced with the air rising from the surface. When the balance is just right though between the rising air coming into a thunderstorm and the winds changing with height then a tornado can form. Tornadoes can be weak or strong and last a few seconds up to many minutes.
A hurricane is a huge organized thunderstorm complex that develops over the ocean. The ingredients are warm ocean water, weak upper level winds, and low pressure. The warm ocean water supplies the moisture for the hurricane. The weak upper levels winds allow the developing hurricane to not tear apart, and the low pressure allows thunderstorms to develop. As the thunderstorms develop they will be influenced over many hours and days by the earth's rotation. This is what allows the thunderstorms to start developing into an organized circulation where they rotate around a central point, called the eye. If the circulation stays over warm water and the upper level winds stay weak then the hurricane's winds will continue to get stronger. The hurricane will weaken if it comes on land, moves over water that is too cold to sustain it, or if the upper level winds get strong enough to start breaking the circulation apart.
