https://www.viahero.com/travel-to-italy/italy-travel-faq
In October the temperatures in the Amalfi Coast are usually warm, around 2o0C / 70oF during the day, and it drops to 15oC /63oF at night time.
American citizens do not require a visa to enter Italy if they plan to stay under 90 days. However, your passport must be valid for at least six months after your planned departure date. Please contact https://travel.state.gov/content/travel/en for more information on how to obtain or renew your passport.