I went to a class reunion in Louisiana this past spring. I lived in Louisiana for years and visit regularly.
Having said that,
and having stressed and noodled a bit on reunion dressing for mine, I'd say, don't think "Louisiana" per se or sticking out on the basis of the state. Weather in general, sure--It can be humid year-round but the temps are mild in October; shabbychick is right , though, in that north LA would tend to be cooler than the delta in the fall. The layer option is always a good idea.
What I would focus on is: what is the stated dress code (and whether you think they mean it! My reunion used the dreaded "dressy casual," which can be helpfully or agonizingly liberal--so dresses or dressy slacks worked; if it had been "cocktail attire," I would have gussied up more; what is the venue (is it the hotel banquet vs. the Friday night bar scene; is it being held outdoors or inside is key because air conditioning is air conditioning, so indoors is more generic than being like "Louisiana" and also lends itself to more formality if you're surrounded by chandeliers and such.
Then the key issue is, in the range of outfits that fits above, what looks really great on YOU right now, at your current age and body type and personality--including how the shoes and accessories work with it? And is it a non-fidget/fuss outfit--something that is "comfortable" not because it's informal or like pajamas, but because you know how it works when you wear it and it is not prone to wardrobe malfunctions (heels that wobble, necklines that gape). If you go with that, you'll appear "effortlessly stylish" and won't stick out in a wrong way.
