I would say do it now! You know what didn't get worn this last summer, but by next summer you'll have more important things to remember and which skirts were in high use last summer will be a distant memory.
Plus you're on a roll, so it means less work later (when you probably aren't on a roll), AND editing now means you'll have more storage space from now until May!
From experience: I moved from Ohio to Arizona and THEN cleaned out my wardrobe - I wish I had done it earlier, rather than paying to ship clothes I ended up donating! And then it took me a year to sell/donate more of the winter stuff - I could have had a much cleaner closet for the last year if I had just taken care of it.
