Raced around island in wet weather (4)
I believe the answer is:
rain
'wet weather' is the definition.
(rain is wet weather)
'raced around island' is the wordplay.
'raced' becomes 'ran' ('run' can be a synonym of 'race').
'around' is an insertion indicator.
'island' becomes 'i' (geographical abbreviation).
'ran' going around 'i' is 'RAIN'.
'in' acts as a link.
(Other definitions for rain that I've seen before include "bad weather" , "Precipitation" , "Fall wetly" , "downfall?" , "Storm" .)