CR 16.
It's a gargantuan elemental with all four elemental subtypes, at its most basic. It has a few special attacks, but you should be able to go with it from there.
Except that they don't even really need to reprint it at all if you think about it. Most characters take a PrC around 6th level or so, so this PrC's 10th level would be roughly a 16th level PC. That means a CR 16 monster would be roughly appropriate. Given that its for the Skylord PrC, you can surmise its something to do with elemental air. That alone is enough to give you enough to go on; it's not like the power would be to summon a Small elemental.
Also, you may blithely say that they should have just reprinted the monster, but it isn't that simple. Virtually every book has stuff that gets trimmed from it before it goes to print, so the final page counts are pretty crammed with stuff that made the cut. Reprinting a full-page monster would mean something else had to go...getting rid of new stuff for material that has already seen print. That would have been much more unfair to the people who already owned the MM2 than this way is to the people who don't. You can ask someone to give you the details of the Tempest (and don't worry about copyright law; that doesn't care if you borrow a friend's copy of the book or even just flip through it in a bookstore) - you can't ask someone to give you the details of the page of new material that would have been cut to have the Tempest reprinted.