While we don't know for sure who will be No. 1 on this week's Billboard 200 album chart, we're already looking ahead to next week's list.

Jay-Z & Kanye West's new collaboration album, "Watch the Throne," released today (Aug. 8) exclusively through Apple's iTunes Store, is on track to sell at least 400,000 to 500,000 copies in its first week in the U.S., according to industry prognosticators. That would instantly become the second-largest sales week of the year, behind Lady Gaga's 1.1 million opener for "Born This Way."

'Watch the Throne': Billboard.com's Track-by-Track Review

"Watch the Throne," which miraculously didn't leak to the Web as so many eagerly-awaited albums have over the years, is exclusive to iTunes until Friday, Aug. 12. That's when all other retailers -- physical and digital -- will start selling "Watch." Of course, most brick-and-mortar retailers could opt to ignore the official street date and begin selling the CD as soon as they receive it, which may be as early as Wednesday.

Best Buy has the exclusive deluxe physical CD edition of the set from Aug. 12-22, which sports the same four additional songs as on iTunes' deluxe version.

Predicting "Throne's" first week is tricky because of its unique release rollout. Traditionally, albums drop to all retailers on Tuesdays. However, "Throne" secured a Monday street date, but only through iTunes. So, its first four days of release will consist mostly of sales via Apple (with physical street-date violation sales mixed in), while the remaining three days of its first week will be a blend of physical and digital.

Jay-Z and Kanye West: A Bromance Timeline

Thus, because of the weird nature of "Throne's" release, stay tuned through the week for further news on its first-week sales pace.

Nielsen SoundScan's sales tracking week runs from Monday through Sunday. We'll have "Throne's" official first-week sales figure on Wednesday, Aug. 17.