"Warned regions” reminds me more of headlineese than bureaucratese (specifically, the headlineese phrase, “area man” springs to mind: a phrase found in headlines like “killer ‘kept to himself’ says area man"). The bureaucratese version of “warned regions” would likely be quite long: you would need a cumbersome name for the regions themselves and a cumbersome name for the specific type of notice given, and you would also have to toss in some vagueness about agency. (Imminent Risk of Harm Advisories have been distributed to the population centers deemed to face a Class II or higher risk of adverse climatic impact.)
Both headlineese and bureaucratese favor confusing constructions, but, broadly speaking, bureaucratese tends to be needlessly round-about (using eight words where two would have been fine) while headlineese tends to be so condensed as to be cryptic (using two where eight would have been helpful). Of course, there are exceptions to everything.
A governmental agency whose role is providing weather alerts to the public via media sources would likely find itself using a blend of bureaucratese and headlineese: news releases are its stock in trade, but such items must be ran through a bureaucratic filter. Happily, perhaps, this particular alert smacks more of headlineese to me.