I found myself in a sandstorm over the deserts of central Saudi Arabia once, in an R44.
Straight and level at about 3000ft agl, in blinding sunshine but otherwise calm conditions, all of a sudden I was surrounded by dozens of huge spinning towers of sand. From ground level to twice my height.
They looked really heavy and laden with energy.
The really alarming thing was that they seemed to move faster than my VNE, though that may have been an illusion. I have a clear memory of looking out of my side window and seeing one of them overtaking me. They lurched this way and that, randomly changing direction.
My only option was to select max rate of climb, and hope to get above them before one or more of them hit me, while turning sharply left and right to keep from being trashed as they crisscrossed my path.
Finally felt safely above them at about 7000ft, where there were no more spinning sand devils, just a sky full of sandy dust, which obscured all visual references thanks to the sunlight reflecting off its shiny grains.
I was back into clear air a few miles later.
I think flying in the cool of the early morning may be the surest way of avoiding the problem.
UK