I suppose that you could create an animation of the sandstorm, and have it play over the desert with a Parallel Process event on infinite loop. If it were me doing it, I think it'd be cool to have an invisible event on a custom move route crisscrossing the desert, constantly playing the sandstorm animation centered on itself. You'd have a moving sandstorm, which would look, in my opinion, tres cool.
But that's just me. I'm old and senile.