Agency worker set off in violent storm (7)
I believe the answer is:
tempest
'violent storm' is the definition.
(I know that tempest is a type of windstorm)
'agency worker set off in' is the wordplay.
'agency worker' becomes 'temp' (temporary worker sent from an agency).
'off' is an anagram indicator.
'in' means one lot of letters goes inside another.
'set' anagrammed gives 'est'.
'temp' placed into 'est' is 'TEMPEST'.
(Other definitions for tempest that I've seen before include "commotion" , "Violent windy storm" , "Cyclone" , "Shakespeare's 5" , "Met pets in fierce storm" .)