Prophecy warning actors (8)
I believe the answer is:
forecast
'prophecy' is the definition.
(I've seen this before)
'warning actors' is the wordplay.
'warning' becomes 'fore' (I've seen this in other clues).
'actors' becomes 'cast' (I've seen this before).
'fore'+'cast'='FORECAST'
(Other definitions for forecast that I've seen before include "Predict (event)" , "Tell in advance what will happen" , "Prophecy" , "Prophesy" , "Predict as with weather" .)