What is the tone of Kate Chopin's "The Storm"? I was going to say sympathetic, however I don't have enough info to back that up.

I agree with you that the tone of Chopin's "The Storm" is
sympathetic. 

One place to find evidence to support your
conclusion about tone is in the description.  A speaker's description of characters will
usually reveal his/her attitude toward those characters.

In
paragraph twelve, the speaker describes Calixta as
follows:

She
was a little fuller of figure than five years before when she married; but she had lost
nothing of her vivacity.  Her blue eyes still retained their melting quality;  and her
yellow hair, dishevelled by the wind and rain, kinked more stubbornly than ever about
her ears and temples.

The
speaker describes her character as vivacious, and the character's eyes melt.  The
speaker uses specific detail--"about her ears and temples"--to give her character
verisimilitude, or realism, and to create imagery; to make the face concrete.  The
speaker encourages the reader to imagine Calixta in her
vivaciousness.

In paragraph twenty, when Calixta staggers
backward, she is "encircled" by Alcee's arm--a protective, tender motion.  When
she cannot compose herself,

readability="9">

Alcee clasped her shoulders and looked into her
face.  The contact of her warm, palpitating body when he had unthinkingly drawn her into
his arms, had aroused all the one-time infatuation and desire for her
flesh.

The moment is
described positively.  Again, specific detail creates imagery--Alcee "looked into her
face"; her body is "warm" and "palpitating"; his infatuation and desire are "aroused." 
The imagery makes the movement concrete, as well as adding verisimilitude.  And the
images are positive and tender.

This is the moment that
leads directly into what society calls adultery, but the speaker considers fulfillment
and necessary passion. 

The speaker's description reveals
the tone to be sympathetic.