Hey!!
I couldn't get to your pic but sounds pretty normal to me.. I know when is hot outside my leaves look like they are thirsty even after a big waterin or rain.
Chena

The leaves folding down around the midrib is normal for some but not all varieties. Oldest leaves turning yellow and dying is normal for all varieties.

Did you just get it fairly recently? I've had the same issue with bananas grown in a green house under filtered light. When you throw them right into full sun the leaves can wilt to adjust for the change. All new growth/leaves should not wilt.

I've had it for a few months-- I ordered it thru the mail so I don't know if it was from a greenhouse, but I'd assume so. Just the other day I pulled the last original leaf off...
it seems like its only been doing it for the last month or so... oh well, I guess its ok.

Even my ones in the greenhouse will wilt like that in the middle of the day with the sun beating down on them, even when they have enough water. It seems like they just can't get the water to the leaves fast enough. As long as they recover when the sun goes off of them, they are fine.
If you're planning on bringing your banana inside the house potted, and keeping it going over the winter, I'd give it fertilizer over the summer so that it will grow better for you. But it won't really need much fertilizer during the winter when it really won't be growing much. only about 1/5th of what it needed during the summer.

Soak the plant with water every day, making sure to soak the root zone and not just watering from above. My bananas do this when temps are in the 70s and warmer. When temps cool down, the leaves will flatten out and look healthier. Remember that bananas are more or less rainforest plants. Since temps here have only been in the 60s for the past few days, I haven't had to water but every other day, and the leaves haven't drooped.

If you are a morning waterer, you might want to consider watering after 1 or so. It will cool the plant down during the hot time & the soil will still have time to dry.
I always spritz my leaves, especially during the summer. I had one in a pot that was burning badly  I moved it to the shade. I later found it was rootbound, repotted it, & have it now back in the sun.