What are the strategies of "The Storm" by Kate Chopin, such as word choice, repetition, simile? And how do they related to the theme?

Chopin establishes a foreboding or threatening mood in the first paragraph, when the narrator describes the clouds as "sombre" and as "rolling with sinister intention." In addition to their menacing appearance, they are also "accompanied by a sullen, threatening roar." This mood helps to foreshadow not only the literal storm but also the metaphorical storm of passion that erupts between Calixta and Alcee. It, too, could threaten the people in the story but in a very different way than the storm outside. The story, in part, conveys the theme that passion can erupt as quickly and in as dramatic a fashion as a storm; it can also, however, pass as quickly as such a storm. The story presents passion as an extremely powerful force as well as one that is easily spent and short-lived. Chopin's presentation of the storm helps to illuminate these ideas.

Among Kate Chopin's word choices is the dialect of the Acadians of Louisiana; this is a technique of the "local color" or regionalism movement of the late nineteenth century. In the story's opening scene, Bibi, who is concerned about his mother as a storm approaches, tells his father, Bobinôt, "No; she ent got Sylvie. Sylvie was helpin' her yistiday" to emphasize his belief that Calixta is at home alone.
Chopin utilizes repetition in the many times she uses the word "storm" in the story.  It is literal, as it is a crucial part of the setting of the story.  Bibi and Bobinôt are stranded at Friedheimer's store because of it, and Alcée takes shelter with Calixta because of it.  It is also a metaphor for the moments of passion that overtake Calixta and Alcée.
"Her lips were as red and moist as pomegranate seed" is a simile Chopin uses to describe how Alcée sees Calixta in their moments of intimacy.  
If a theme of "The Storm" is the presentation of sexual attraction as a force of nature, the repeated use of the word "storm" is very useful as a metaphor for the charged atmosphere when Calixta and Alcée meet. The use of the Acadian dialect that Bibi, Calixta, and Bobinôt speak and the contrasting Creole background of Alcée suggests that sexual attraction recognizes no cultural or social boundaries.  And the simile of Calixta's lips compared to another product of nature helps to illustrate the elemental attraction that flows between Calixta and Alcée.