Reportedly warm and sunny? It's brief! (7)
I believe the answer is:
summary
'brief' is the definition.
(I've seen this before)
'reportedly warm and sunny?' is the wordplay.
'reportedly' indicates a 'sounds like' (homophone) clue.
'warm and sunny?' becomes 'summery'.
'summery' is a homophone of 'SUMMARY'.
'it's' is the link.
(Other definitions for summary that I've seen before include "Recapitulation" , "Synopsis, outline" , "Precis, gist" , "Brief" , "Arbitrary" .)