Properties wise, it is identical to other ink in the series.
By itself, Storm looks very similar to R&K's Scabiosa. How does it compare to other shades of purple?
I just happen to have a whole arsenal of purple, so here is the comparison:
Because the comparison is written by Pelikan's Double Broad nib, so all purple look extra concentrated. The way to discern the difference is to look at the shading. Storm is definitely a dusky purple, but it has a tint of brown when put next to Scabiosa. Scabiosa has a little bit of gray undertone, which makes it a good alternative to black ink. Storm can also pass as black when comparing to Private Reserve, which is this bright aubergine purple with violet shading. To my eyes, Storm looks like the color of a cooked eggplant skin when it is juxtaposed to De Atramentis' magenta violet. De Atramentis's magenta actually has a little bit less blue than Private Reserve, but not as red as I expected. Storm looks more subtle than J. Herbin's Violet purple, which is a light uplifting lavender. Lastly, Mont Blanc's lavender purple is clearly not too lavender, but more like a bordeaux purple.
After comparing to all these shades of purple, I can see why Caran d'Ache names this purple "Storm." This does not happen all the time when the storm comes, but sometime the air becomes absolutely calm before the advent of storm, and the sky looks gloomy, but at time with a tint of purple. Storm inspires these associations. It is a calming and subtle color that brings a sense of serenity.