What does a tornado on the map mean?

There is a tornado like swirl on my map. It has dust clouds lighting coming from it. It is in a random spot next to a poke stop. Nothing is popping up in that circle. It is not attached to me like it looks like in the picture. My brother has Pokémon Go and it is not showing up on his. What does this tornado indicate?

tonado screenshot


The tornado matches the exact animation of a gym under attack. It must have been a glitch in the game, but in my personal experience, I have never encountered this problem.

The game always has weird glitches, and if your brother did not see the tornado, it is more evidence that it is a glitch.