What happens in a fire tornado?

In a fire tornado, more properly called a firewhirl, the heat from the fire creates an upward current of air called an updraft. Air sourrounding the fire is pulled in to replace the rising hot air. Under the right conditions, an eddy in the wind may join up with part of the updraft. The eddy contracts as it is pulled inward by the rising air, creating a small but intense vortex fill with smoke or fire.