It's a hot day. You can't wait to go for a ride. Even though it's hot, wear a couple of layers (or pack some layers in a backpack or in your bike's luggage, if it has it). If you're riding a long distance, or if you're going to be out for a long period of time, chances are good the temperature will change. You'll feel it more than anyone else when you're out on two wheels, even if you're riding a fully faired bike with a big windscreen. On average, going highway speeds makes you feel like the temperature is 10 degrees less than your local weather forecast says it is. Keep that in mind.

Also, most motorcycle gear manufacturers make full mesh jackets for riding in the hottest weather. These have armor in them to protect you if you fall, but allow massive airflow to keep you cool. Staying covered when it's hot helps keep you from dehydrating or getting sunburned, too. What do you have to lose?