It may seem difficult to imagine if you live in a rainy place, but the beginning of Sicily's "rainy" season is a much-awaited event. For at least two months there's no rain in most parts of Sicily - except perhaps for an occasional drizzle on Mount Etna. Then, usually around the beginning of September, there's a legitimate shower.
Last year (2009), it was on August 31st. This year it was on Thursday, September 2nd or, more precisely, the early morning hours of September 3rd. That meant droplets on the plane trees, and the beginning of cooler nights.