We have experience the same thing very similar of which happen in the East Rand (SA) on Sunday evening.
Yesterday afternoon at about 3pm. While working with the tractor busy mulching in block A, while working in the direction of the store. Strong winds stand up behind the tractor and move side-ways past the tractor.
I kept an eye on it as it getting stronger and higher as it moves in the direction of the upper store (where we store the chemicals).
I suddenly realize but this wind looks different than some winds that I have ever seen. I also realize that Piet and Gerhardus are busy inside the bottom store busy cleaning the fingers of the water filters. It strike my mind that I should scream to tell them to get out of the store as danger is coming. This all happen so fast that by the time that I want to do what I decided to do to alert them, it was all over. This all happens in 4 seconds.
My assumption is that it seems that; it looks like the wind starts at the vineyards just at the trees of the fence between us and Rainbow chickens. It seems like it was busy building momentum and picking up speed.
The bottom store was too big and hollow and therefore it split the head from the tale and it did not continue to grow further after the store.
Piet and Gerhardus were fine as it could not do any harm to the bottom store. Piet and Gerhardus could not hear the sound which came from the fall of the top store hall as they have experience a different sound as the wind hit the bottom store.
It was scary
I alert the authorities via rescue services of what we have experience.
I hope you believe me