I see the difference this way. The first sentence indicates that summer arrived, the second one as summer arrived over a period of time.

Hi Shia, I would not use "came along" with a routine event like summer. My understanding and thinking are​ as follows: A: came: arrived B: came along = joined (or similar meaning). For example, my friend came along -> my friend joined us

I think they both mean the same. It is hard to tell without more context. "came along" sounds more casual, like you're telling a story.