More water, I live 15 miles east of you and I water my in ground trees daily. I'm in the same sandy soil as you. It's been warm the last few days but this week should bring us some relief. Once it cools down I water my trees every other day like in December, January and February. I then bump it to daily again in March when it starts to warm up and I get a growth flush. That's also when I throw my first fertilizer down for the year. Try watering daily and see how that does, if it doesn't help it could be something else.
Evan

That would be waaaaaaay too much watering. Water deeper, longer, less frequently.

Chances are good that the roots simply haven't established yet, and so the roots can't keep up with the day-time warmth on the leaves pulling moisture.

Josh

I think you are both right.

It needs to be better established in order to get enough water out of the soil. If Summer wasn't winding down, I'd recommend shade cloth until established. Think of temps of 110F, humidity below 10%, long days, no shade and imagine how much water that takes.

Palm Springs area could easily require daily watering if you are in an area with really sandy soil with no bottom. The best way to change that is adding material to help hold some water. Consider adding lots of mulch to slow the sun baking the moisture out of the ground near the tree.

Some of the golf courses are adding Profile amendments, AKA Turface, at the rate of 30-50%.

Absolutely add mulch! Great advice....
Sometimes I just assume that folks are automatically doing things like removing grass and adding mulch.

Josh

I was going to suggest mulch too. I just picked up some bags of mulch yesterday that are going around my trees today. A great way to extend time between waterings.
Evan