I recently wrote:
But I wasn't sure if I was making this up, or if my brain was being a supercilious Yankee asshole. I considered adding that I associated that pronunciation with Louisiana, but I was afraid I was already too far out on a limb.
But it seems that I wasn't making it up, at least not this time, and that it is associated with Louisiana, among other places. I did a search for “u.s. regional dialect "triphthong"” (note nothing in there about ‘Southern’) and found that this regional triphthongization is a thing everyone knows about. (“Triphthongization”, wow.) Dialect blog says:
Dialect blog may not be a reliable or authoritative source, but such sources are easy to find. For example, Sounding Southern (Rachael Meghan Allbritten, 2011) says, of a 24-year-old woman in Montgomery, Alabama, “Sierra has some extremely high /ɪ/ tokens such as her triphthongal kid”. (The vowel there is the same as in grits.) Later on she mentions further examples: cat [kæɪjət], lip [lɪjəp], hill [hɪjəl], ill ɪjəl], bet [bɛjət], hell [hɛjəl], and cents [sɪjəns], and others.
I need to be careful not to let this confirmation go to my head. I am not in general very good at hearing this kind of thing, or at understanding what I have heard. Allbritten says:
My current non-understanding of phonology and IPA notation is a serious hole in my knowledge, which continually prevents me from understand other things as well as I want to. I should make a bigger effort to fix this.