It doesn't rain a lot here during this time of year. Even when lecturing not all professors wear suits. Dress pants and a nice shirt, or a pants and blouse or a skirt will do just fine, unless you feel too casual that way. If you decide to wear khaki pants or jeans, you'll fit right into Campus. Most students wear khaki shorts and, for the girls, tank tops, or even sports clothes to class.
Cotton is definitely a plus.
Silk and linen are not recommended because you will sweat outside, and freeze inside. Bring a sweater or a light jacket with you whenever you plan on spending more than 5 minutes inside any building. Air-conditioning is running in full force. From experience I can tell you, after the first refreshing chill you will get quite cold, and many people even get sick. I recommend that you get some US currency before coming here.