Looking at the graph on this thread http://gamrconnect.vgchartz.com/thread.php?id=228581&page=1 , you can see that pretty much every console has settled their baseline after their 10th week.
Now, I know the Switch suposedly has been having low stocking issues so I will take that into consideration and go with a baseline of around 190K with a relatively big bump for Splatoon week so...
July: 900K,
August: 800K