Theory originally from: http://www.abovetopsecret.com/forum/thread1002160/pg3#pid17664908
Note: As far as I am aware, Huobi and other markets are open 24/7. So I have no idea what the trader here means that "BTC is closed to many of the bigger overseas markets."
Anyhow, that is neither here nor there. At this point I imagine sites like Overstock and TigerDirect dominate bitcoin transactions ( https://blockchain.info/charts/n-transactions-excluding-popular?timespan=all&showDataPoints=false&daysAverageString=7&show_header=true&scale=0&address= ). Since most retail outfits use bitpay and bitpay immediately converts back to the vendors native fiat currency. That eventually pushes the bitcoin price down. Assuming regular purchasing habits, at some point the customer would have to buy back in. It is probably fanciful to think that there would be a simple weekly pattern behind this, but the idea was interesting enough that it warranted a look.