From what I understand the sandstorm will occur during summer in the whole antlion desert if it's not raining and the world is not "wet" (wet means rain happened recently). The sandstorm is supposed to prevent summer smoldering as long as the player is inside it, but a rare summer rain can ruin all of this. If it starts raining, the sandstorm will stop. Rain still prevents smoldering, but when the rain ends there's going to be a lapse of time where the world is considered wet, so the sandstorm will not come back immediately. During this time smoldering can actually happen and I don't think this is intended.
Sorry if this is the wrong section, I wasn't sure if this would be considered a bug.