The most violent tornado have winds of more than 400 kiolmet

tornado英[tɔ:'neidəu] 美[tɔ:'neidəu]
n.旋风,龙卷风
n.旋风,龙卷风
复　数：tornadoes,tornados
因此你的句子,应该有误,要么是The most violent tornados have winds of more than 400 kiolmetres a minute.
要么是The most violent tornado has winds of more than 400 kiolmetres a minute.