Tropical island I see in middle of Slough (4)
I believe the answer is:
oahu
'tropical island' is the definition.
(I know that Oahu is tropical)
'i see in middle of slough' is the wordplay.
'i see' becomes 'ah' (exclamation used to indicate understanding).
'in' is an insertion indicator.
'middle of' indicates the central letters.
The central letters of 'slough' are 'ou'.
'ah' inserted into 'ou' is 'OAHU'.
(Other definitions for oahu that I've seen before include "Honolulu's island" , "Hawaiian island" , "Chief island of Hawaii" , "Pacific island" , "popular Pacific location" .)