I can't do anything about that, I don't even think you can turn it off. Do you think it is worthwhile to have storms spiral given clouds move west to east?
Well, I think its harmless. Most people never zoom out that far.
I think whether or not it is worth shifting the storm pattern to be circular is independent of how clouds move in a very zoomed out fashion.
It may be worthwhile to add a game option with "storm density" zero, low, medium or high
I like this idea. It could be fun to have a game played in a storm-ridden hellhole, where only tiles protected by mesa and in sinks were safe from massive storm pillaging.
If I change it to a spiral, then I will divide the map into four quadrants
We're thinking along the same lines. Just make sure you have something to control storms that happen to approach the center of the map just staying there forever.
Removing them when they hit polar waste would do this.
It would also be good for the center of the map to generally more protected from storms. Tweaking the weighting could be a good way of doing this: if storms in the NW quadrant go SW, S or W, then maybe they should be SW=50%, W = 28%, S=22%. And similarly for other quadrants This would help cause storms to spiral outwards (in a probabilistic sense).
Alternatively, you could have storms spawn only in deep desert tiles, and spiral inwards, to crash onto land. Having them only spawn on deep desert would make them much more likely to appear on the outer edges of the map and then come in, which is how the real storms on Arrakis happen.
Ideally, you could also have the mapscript generate some parameter, so that the storms woudl either act east-west as current on Duneipegalo, or in a spiral if on Arrakis.