Just a like a regular tornado tornadic waterspouts start from the cloud and works its way down towards to the service. They typically form from severe storms and supercells and they just form over ...

Fujita F1 - i.e. wind speeds greater than 116km/h (63 knots) or stronger. Note: some tornadic systems such as funnel clouds, waterspouts and small land-based tornadoes are possible with thunderstorms ...