Your question relates to the richly symbolic way in which the storm, which of course is such an important part of the setting of this excellent short story, impinges on the lives of the two central characters: Calixta and Alcee. Ever since their last encounter, their passions for each other have been simmering just like the way in which, before a massive summer storm, the air becomes heavy and oppressive. The release of the storm triggers a release in their passions and emotions that is paralleled by the sounds of the tempest outside of the house:
They did not heed the crashing torrents, and the roar of the elements made her laugh as she lay in his arms. She was a revelation in that dim, mysterious chamber; as white as the couch she lay upon.
The setting is thus very important in terms of the way it symbolises the unleashing of emotions and feelings repressed for so long between Calixta and Alcee. Note too, the way in which this symbolism is continued after their secret tryst. Both of their marriages are shown to benefit from this release of passion, just in the same way that we are all grateful for an intense summer storm and the way that it restores everything to its fresh state. Chopin obviously thought that a bit of marital infidelity here and there could actually be constructive rather than destructive, and the setting shows this.