In reply to maybe_si:
Getting better (cooler) by the day at that time of year. If going to stay in San Vito town avoid the Cous Cous festival (finishes 29 Sept, busy and high demand for apts). There are some shady crags, and it is easy to take a siesta and climb in the evening (crags are very accessible) The sea is lovely as is the El Bahira pool!
Guidebook-for just San Vito, Gebro Verlag, for all Sicily, Versante Sud.
As for a comparison with Spain, Spain is a big country with a wide range of climatic range!