I would absolutely recommend Merino tops for cycle touring, for all conditions.
I own a number of Icebreaker tops, in various sleeve lengths and weights, and some leggings too. The great thing is that they layer so well - so you can warm up or cool off easily without too much bulk - and always wick sweat away so you stay comfortable in he heat or cold.
I have used my Icebreaker clothing in SE Asia (hot, humid temps) in NZ South Island (wet, cold temps) and Australian outback (dry, hot days and cool nights), and it has been perfect for all these conditions, on the bike, around camp, and in towns.
Plus, the added bonus of being light-weight, packing small, and resisting odour. I can't recommend merino clothing highly enough for cycle touring.