It starts to cool down a bit in May and generally stays around the mid 20s (Celsius) but don't be surprised if it goes from 20 in the morning to 30 at midday to 10 at night. But if I recall correctly it gets a bit windy around those times. The Gold Coast is a tourist hotspot and is incredibly busy during the school holidays so don't be surprised if everything is busy as all hell, so plan according to the Queensland School holidays. My family tends to go to the Sunshine Coast more often than the Gold Coast mainly because it is a more relaxed environment and is as equally beautiful. But our weather is so crazy, I remember we went on holidays to Alexandra Headlands and the forecast was sunny but then as luck would have it, it rained all week.