The weather in New Orleans is always changing. From July through September is hurricane season, when hurricanes are more likely to pop up. From the end of November through February is the so-called "winter time" down in the South. Sometimes it's warm enough for people to mow their lawns in shorts and T-shirts. Don't be foolish, though. New Orleans can get pretty chilly. It usually does not snow, but there have been some years that it has.
The weather here is on its best behavior in the Spring because it's warm enough to wear summer dresses but cool enough to avoid returning home drenched in sweat. If you stay for a summer semester, be prepared for it to get pretty hot, especially with the high humidity. As long as you keep up with the weather, there should be no worries. Rainboots are a good item to have, but you do not have to have them..