Traditional business attire is not always suited for the late April weather in Arizona. Scottsdale, despite its fashion reputation, is much more relaxed than the East Coast. Understand that you will be walking outsite in a rather hot sun, along swimming pools with sunbathers, then you'll enter a very cool, air-conditioned convention center.
You may want to wear short sleeves with a light sweater or business jacket, with layers you can shed when walking outside from the rooms to the convention center. Above all, you want to be comfortable, especially if you have to pitch your book to an agent or publisher. In previous years, a few agents and editors even took their appointments under an umbrella at an outside table in 90 degree heat. You never know where you are going to be.
Nylons, so prized in New York, are a nuisance in the Arizona heat. Do not wear casual shorts for the events, of course, but you may want to wear sandals rather than boots, a nice summer dress rather than a business suit (with a jacket or sweater on the side). Business casual is the word in Arizona, with the emphasis on casual.