Tornadoes such as the one that tore through Tembisa, on the East Rand, on Tuesday afternoon hit South Africa on average twice a year. Such extreme weather events are difficult to forecast, said climate modeller Francis Engelbrecht, of the CSIR.Because the tornado struck an urban area it was caught on video camera and the evidence is that its severity would put it at F2 on the Fujita scale."This means that it uprooted some trees in its path. If it had uprooted all the trees it would have been an F3," Engelbrecht said.An F5 tornado would be able to fling a car into the air.Engelbrecht said that no forecaster would have been able to predict the tornado's arrival.In the US, radar surveillance gives a 30-minute warning but South Africa does not have that technology.Tembisa residents were still reeling in shock yesterday as they tried to rebuild their homes.The tornado blew off the roof of Phumulani Mall, damaged about 200 homes and dozens of cars, left about 400 people homeless, and destroyed part of the Tembisa Provincial Hospital and a nearby filling station.At least 20 people were injured...