These are no normal sandstorms, these are physical manifestations of dust's will. The Age of Dust ended when the dust storms all concentrated into only a few smaller storms. However, in doing so they gained sentience of their own, all connected with one another via a kind of neural link called the 'Grit Synapse'. They do not need wind to fly, for they are the wind, the hand of dust.
Why did whoever designed the Pyramidion only put guns on port side and not starboard?