I don't have my ATPL MET book in front of me but do remember this question and can give some guidance on where to look for a more informed answer.
It has to do with the cross section of a jetstream. Jetstreams run from WEST to EAST and so if you are flying towards the south you are probably flying into a jetstream. (hence the increasing westerly wind).
The clue as to where the CAT lies is in the increasing TAT. If I remember correctly increasing TAT means you are near the top of the jetsream and in the southern hemisphere the CAT is encountered on the top southern side of the jetstream. So in this case you would want to descend to avoid the CAT
I know its not the complete answer but hopefully has given you a hint as to the correct answer....I am sure this was covered in my notes so it should be in yours.
Cheers
Alpha