Clue: In teeming rain, a compiler put on shirt: will this keep it off? (9)
Answer: TARPAULIN
Explanation: Definition: will this keep it off?
A charade of T ('shirt') plus ARPAULIN, an envelope ('in') of PAUL ('a compiler' of Guardian crosswords) in ARIN, an anagram (teeming') of 'rain', with 'put on' giving the order of the particles.