The Miami Herald and numerous other outlets are saying it was Magistrate Judge Reinhart.  They point to docket entries showing Sealed warrants signed on 8/5 by Reinhart.  Perhaps.  

One thing that always has bothered me about search warrants is that they should not Remained Sealed once they are executed unless there is a real law-enforcement need to keep them sealed.  And they should almost always be made available to the party affected.  But I bet Trump's legal team hasn't even seen the actual affidavit in support of the warrant yet, which is bananas.

The warrant will likely remained sealed until (if?) an indictment is brought.  If there is no indictment, the warrant may never become public.