My experience with Robusta is that in the Summer, if it is anywhere near high 70' or higher, you can't water them too much. Now thats just MY past, maybe somebody else disagrees.
From the pics, it looks like to me just normal old age of a frond. I'de keep things the way they are and when the leaf turns totally brown, cut it off. I'de bet your just seeing normal age.

As the self promoted expert on over watered plants, I can say without a doubt you do not have a problem with over watering. In my experience the tips will just turn brown, no yellowing, in addition brown spots will appear at varying points on the rest of the fan. The browning effect will move down the left tip until the entire fan turns brown. I have a bunch of examples in my greenhouse if you want to look?? 😆

Temps have been around 85-90 for a while now. So it has been much warmer than usual however this tree came from Florida so it's used to that. Being a "desert palm" I was afraid I was over watering it.

Ok, I will keep an eye on it!
Thanks

"Desert palm" is a confusing term. It refers only to hot and dry air, but all palms need plenty of water. Some get it from a stream or lake or water hole nearby and others have very long roots to get to underground water.

In some regions, people are watering thoroughly the young palms until they get their roots long enough to stop watering then subsequently. So that's why they are standing there on sandy soil in the desert. Naturally, a palm seed or a young palm can only grow where is water nearby or often rainfalls occur and the water gets stored invisibly under rocks or so, Chamaerops humilis, e.g.

I neglected to water my W. robusta this past heat wave, and now I've had to cut 4 fronds off, half of what was there.
Cheers, Barrie.

So your saying keep on the watering..?