Tom maybe has a fit of temper — explosive meltdown? (11)
I believe the answer is:
catastrophe
'meltdown?' is the definition.
(I know that meltdown is a type of catastrophe)
'tom maybe has a fit of temper explosive' is the wordplay.
'tom maybe' becomes 'cat' (a tom is a male cat).
'has' means one lot of letters go next to another.
'fit of temper' becomes 'strop'.
'explosive' becomes 'he' (abbreviation for high explosive).
'cat'+'a'+'strop'+'he'='CATASTROPHE'
(Other definitions for catastrophe that I've seen before include "Sudden disaster" , "Calamity" , "disastrous event?" , "Utter disaster" , "Denouement" .)