This writer's turning up twice outside a US city (5)
I believe the answer is:
miami
'us city' is the definition.
(I've seen this before)
'this writer's turning up twice outside a' is the wordplay.
'this writer's' becomes 'I'm' ('I am' referring to the writer of the clue).
'turning up' is a reversal indicator.
'twice' shows that letters should be duplicated.
'outside' means one lot of letters goes inside another (some letters go outside others).
'im' backwards is 'mi'.
'mi' doubled is 'mimi'.
'mimi' placed around 'a' is 'MIAMI'.
(Other definitions for miami that I've seen before include "Port in Florida" , "I put out of action when returning" , "state" , "Floridian city" , "US town" .)