My pics from our two October trips (2008 and 2009), are a mix: The first couple days of the first trip, we were HOT, shorts and tank tops, and sweating still. By the end of the week we were in jeans and long sleeve t-shirts. The next year was a little more stable than the first, and I generally wore capri's and tshirts, but had to have a sweatshirt for evenings. For DD, we had dresses that we could layer leggings under when it got cooler, often in the mornings and evenings we added those along with a sweatshirt. DS we often started in shorts but since we always go back for a nap/rest in the late afternoons, we would change him to pants/jeans for evenings.
So I know this doesn't make packing easy! We are going again in October and will face the same issues.
A light sweatshirt is generally fine though, no need for heavy jackets.