Forecaster is upset over Times line (5)
I believe the answer is:
sibyl
'forecaster' is the definition.
(sibyl is a kind of forecaster)
'is upset over times line' is the wordplay.
'upset' shows that the letters should be reversed in order.
'over' is a charade indicator (letters next to each other).
'times' becomes 'by' (I've seen this in other clues**).
'line' becomes 'l'.
'is' backwards is 'si'.
'si'+'by'+'l'='SIBYL'
(Other definitions for sibyl that I've seen before include "Woman mouthpiece of a god, uttering prophecies" , "Ancient seer - prophetess" , "prophet" , "Greek prophetess" , "Seer in classical times" .)