I actually like the plaid dress better than the second one you linked (and it's rare for me to dislike anything with blue in it). The way the color is blocked on the second makes even the model look a bit pear shaped.
Yes, New Orleans is hotter than HELL, but be sure to bring a light sweater for night time and indoor places. Here in the Gulf Coast, a lot of place set the A/C on Artic Blast setting. While it's 88 F outside (with 90% humidity), it might be 58 F inside.