This is a floating holiday, with no exact date. Be ready. Keep your ears open starting about the middle of May. Listen for the sound of the coming summer heat: the first cicada. As soon as you hear that distinctive buzz, know that summer has arrived. You'll instantly feel 10 degrees hotter. Oh glory! Call in sick or leave work immediately, complaining of dizziness. Tune up the swamp cooler, buy a watermelon, fill up the stock tank in the backyard and invite your friends over to soak and spit seeds. Summer is Tucson's finest season, and its arrival is cause for celebration.