Storm warning over old city (6)
I believe the answer is:
furore
'storm' is the definition.
(I've seen this before)
'warning over old city' is the wordplay.
'warning' becomes 'fore' (I've seen this in other clues).
'over' is an insertion indicator.
'old city' becomes 'ur' (ancient city state).
'fore' going around 'ur' is 'FURORE'.
(Other definitions for furore that I've seen before include "Wild excitement; craze" , "Commotion - public outburst - rage" , "A general uproar or noisy scene" , "Uproar, fuss and fury" , "Public indignation" .)