Warmish when the tide's out around the pierhead (5)
I believe the answer is:
tepid
'warmish' is the definition.
(I've seen this in another clue)
'the tide's out around the pierhead' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'around' is an insertion indicator.
'the pierhead' becomes 'p' (head letter of 'pier').
'tide' with letters rearranged gives 'teid'.
'teid' enclosing 'p' is 'TEPID'.
'when' is the link.
(Other definitions for tepid that I've seen before include "What's a bit warm" , "Unenthusiastic - cool" , "Moderately warm" , "lacking enthusiasm" , "Warmish" .)