May is my favorite time to go. I usually need a break about then, the weather is great, and the crowds are low.
I would bring a light jacket or sweatshirt. I have been there in May when the evenings turn cooler, and you might need it. Also a pair of pants or capri's. Or, don't bring a sweatshirt and plan to buy one IF the weather turns cooler in the evenings.
Have a great time.
shelly