I asked around this time, and I think it's ideal to ask now. It's pretty early, but I figured in the next few months my letter writers might be inundated with requests for med school apps and other things. In reality most letter writers won't start writing until a couple of weeks or even days before the deadline you give them, but asking early also has the benefit of making you look well-prepared (assuming you are, since you're already thinking about this).
You don't need to have a finished, polished personal statement to show at this point, but a draft can be very helpful. I emailed my letter writers to ask for a rec because I wasn't currently in contact with any of them, and then I set a time to meet up and give each person a folder with my resume, preliminary list of schools (not necessary, but just to give them an idea of where I was aiming for), and a short letter with the actual letter request containing submission details and deadline. One of my recommenders asked if I had a draft of my personal statement she could read over, so I worked on that a little more and then sent her a rough draft. You could also ask now and let them know that you'll provide them with more information (e.g. the personal statement) later on.