S100 is a pretty good camera, I played around with one a little bit this last year...seemed to shoot pretty well and such. For storm chasing though, Sony's HDR-XR520V is pretty quality, it's slightly better than the Canon in low light. However, as with all consumer handycam comparisons both have their strengths and weaknesses you have to judge. While the Sony has good low light performance, the Canon's performance in bright light is better.
What I like about the S100 are the controls for aperture and shutter as well as variable frame rates, if you are into that sort of thing.