Tornadoes occur in most parts of the world. However they are most frequent over the continental plains of the USA.Tornadoes are typically identified as a funnel of spiraling air descending from the base of clouds to the earth. The tornado is usually narrow, about 1/2 km wide and rarely does it move more than 20 km.Like hurricanes the precise mechanism of how the funnel forms in not understood.
Tropical Storms start within 8º and 15º north and south of the equator where surface sea temperatures reach 27ºC. The air above the warm sea is heated and rises. This causes low pressure.The weather system generates heat which powers the storm, causing wind speeds to increase. This causes the Tropical Storm to sustain itself. Tropical storms rely on plenty of warm, moist air from the sea - this is why they die out over land.The central part of the tropical storm is known as the eye. The eye is usually between 30-50km across. It is an area of calm, with light winds and no rain. It contains descending air. Large cumulonimbus clouds surround the eye. These are caused by moist air condensing as it rises. Wind speeds average 160km per hour around the eye