What is a tornado?

A tornado is a violent rotating column of air extending from a thunderstorm (cumulonimbus cloud) to the earth’s surface, rated amongst the most violent and destructive of all weather phenomena (South African Weather Service, 2008). It may also be referred to as a twister. They can develop any time of day, any month of the year, but are most common in the afternoon and evening. Tornados come in many shapes and sizes, but are typically in the form of a visible condensation funnel, whose narrow end touches the earth and is often encircled by a cloud of debris and dust. Most tornados have wind speeds of less than 177 km/h, are approximately 80m across and travel several kilometres before dissipating. The most extreme can attain wind speeds of more than 480 km/h, stretch more than 3km across and stay on the ground for more than 100km.


(Damage caused by the Manenberg Tornado, October 1999)


Types of tornados

Various types of tornados include the landspout, multiple vortex, and waterspout tornados. Waterspouts are characterized by a spiralling funnel-shaped wind current, connecting to a large cumulus or cumulonimbus cloud. They are generally classified as non-supercellular tornados that develop over bodies of water. Other tornado-like phenomena that exist in nature include the dust devil and fire whirls.


What to do in a tornado

• If available, below-ground shelters, and reinforced "safe rooms" provide the best protection against tornadic winds.
  
• In homes or small buildings, go to the basement. If a basement is not available, go to the smallest, most-interior room on the lowest floor, such as a closet or bathroom. Cover yourself to protect your body from flying debris.
  
• In schools, hospitals, factories or shopping centres, go to the smallest, most-interior rooms and hallways on the lowest floor. Stay away from glass enclosed places or areas with wide-span roofs such as auditoriums and warehouses. Crouch down and cover your head.
  
• In high-rise buildings, go to the smallest, most-interior rooms or hallways. Stay away from exterior walls and windows.
  
• In cars or mobile homes you should abandon them immediately! Cars and mobile homes provide no protection from tornadic winds. If you are in either of those locations, leave them and go to a substantial structure or designated tornado shelter. Do not attempt to seek shelter beneath an overpass or bridge - they provide little or no shelter and have proved to be deadly options.
  
• If caught in the open, lie flat in a culvert, ditch or depression and cover your head.

(Reference)