Sept/Oct Weather

Skirts and light pants should work fine because are cool and appropriate also in less informal situations. Nights and early mornings in October are however cooler. You will need also a light jacket for the evenings. You will see few, if any, Italians wearing shorts in October especially in the cities (Rome, Florence, Siena etc) even if the weather is warm (shorts will be ok at the Cinque Terre). Italians are less informal than Americans and don't consider appropriate to wear shorts downtown in Autumn, even when they have unusually hot weather. I remember one day in early October when I wore shorts in Florence (it was unusually hot for that time of the year, and being a Californian...). All my friends kept commenting on my 'fashion statement' jokingly asking me if I thought I had taken the plane from San Francisco with the intention to go to Hawaii and instead boarded the wrong plane to Italy. Others (on the same occasion) jokingly asked if I had lost track of time and thought we were still in July instead of October. Temperatures were in the high 80's for God sakes. But Italians are a bunch of conformists always afraid of making a "brutta figura" (bad impression, poor showing). So pack shorts only for the Cinque Terre hiking. Rely more on skirts (and slacks or even capri pants)

I too am going in October. I plan to buy some of those pants that you can unzip the leggings off and make them shorts if needed. But it sounds like Shorts are a bit taboo...