This better?
Theist: Believes God exists.
Agnostic: Impossible to know whether God exists.
Atheist: Does not believe God exists.
Bingo.
The agnosticism described does indeed fail to cover weak agnostics, but their stance isn't much more different from atheism, so you can just bundle them there. (though, as I remind you, even strong agnostics are a subset of atheists)
The "right now" agnostic is a variation that could easily fit in weak agnostics or just plain atheism. After all, saying "I don't have the proof to believe in God right now and thus don't know" agnosticism is no different than "I lack belief in God because of lack of proof" atheism. It's a much more useful term to assign agnostics the absolute impossibility of knowing divinity.