Most horrible November so far is equal on temperature (8)
I believe the answer is:
nastiest
'most horrible' is the definition.
(most nasty or horrible)
'november so far is equal on temperature' is the wordplay.
'november' becomes 'N' (phonetic alphabet: alpha, bravo, charlie etc.).
'so far' becomes 'as' (I've seen this in other clues).
'is equal' becomes 'ties' (to tie or draw is to be equal).
'on' is a charade indicator (letters next to each other).
'temperature' becomes 't' (abbreviation).
'n'+'as'+'ties'+'t'='NASTIEST'
(Other definitions for nastiest that I've seen before include "Extremely unpleasant" , "Most revolting" .)