Weather is interrupting break (6)
I believe the answer is:
resist
'weather' is the definition.
(I know that weather has the is a more specific form of the action defy)
'is interrupting break' is the wordplay.
'interrupting' is an insertion indicator.
'break' becomes 'rest' (a rest is taking a break).
'is' going inside 'rest' is 'RESIST'.
(Other definitions for resist that I've seen before include "Withstand a force" , "Check; withstand" , "Hold out for sister" , "Go against" , "Sister (anag)" .)