The storm in Kate Chopin's short story "The Storm" is vitally important. Without it, the story would fail to be as powerful as it is, obviously. There has been much speculation as to what the storm represents, but it is most definitely a symbol, among other things.
First, the storm serves as a plot device. Had Calixta's husband and son not been caught in a storm, Alcee and she would not have been able to have their torrid affair in Calixta's home (and in her and her husband's bed, no less). Also, symbolically, the storm represents Calixta and Alcee's pent up sexual desire and passionate feelings for one another. In addition, the storm represents how fleeting passion can be if one has nothing but it to base a relationship on. Calixta has a deep love with Bobinot; despite Chopin's implied stance that sex in marriage is not as passionate as sex outside of a marrage, Bobinot and Calixta share a deep love that Alcee and Calixta do not share.
Also, storms form quickly, then pass through and go quickly, just as Alcee did. He stopped at Calixta's house; the 2 became intimate quickly, and as soon as the storm passed, it was done and over with and Alcee left.