Hi.
Here you can see some charts/graphics about the weather in Portugal.
http://www.meteo.pt/en/clima/clima.jsp
But if you wish you can see a study from the 60s to 90s in this doc:
http://www.meteo.pt/resources/im/pdf...c_00_00_en.pdf
But I must say than since the late 90s temperatures are rising and the seasons are getting a little mixed-up. For example in late October the average this year has been from 20º to 25º!
Hope it helped.