Bingo !
The road system works better on a sunny day than on a stormy day. That's all.
Trick question, it's never "sunny" in NO!
I spent two weeks in NOLA some 30 years ago. The manager of the lot where I parked my camper said, "Shame you're here during the rainy season." I said "When is the rainy season." He said "Starts about January first and runs through Christmas week."
I was there around Labor Day, and he was right. It rained every day, twice a day. Mornings around 10ish, afternoons about 2. 100% humidity all day, every day. The first thing I bought in NO was an umbrella. I had a great time and throughly enjoyed the food and night life. The people were the friendliest I've ever encountered but that was over thirty years ago. I wouldn't go back now if you paid me.
Regards,