Are the sandstorms in Riyadh a natural phenomenon or a result of people's sins, and are they among the signs of the Hour?

The exact cause of hurricanes cannot be definitively determined, but Allah may send them to instill fear in His servants and remind them of His past punishment of nations, so that they may return to Him. Indeed, the Prophet, peace and blessings be upon him, used to change countenance upon seeing clouds or wind, fearing that they might contain a torment. He forbade cursing the wind and commanded supplication upon seeing anything disliked from it.