Spring - Sep - Nov
Spring is a great time of the year in the Gold Coast. Daytime temperatures build quickly through September along with humidity.
Summer - Dec to Feb.
Summer weather is hot to very hot, high humidity with some spectacular Summer storms. When a storm is brewing the humidity and clouds build during the day. Storms tend to hit in the early evening with amazing lightning shows and torrential rain. The next day, it'll all be perfect again!
If you want to do some sightseeing that includes high level views, such as Q1 or Mount Tambourine, go on a clear day. Go to the theme parks or plan other activities on the cloudy days. Don't forget, it will be hot even if there is rain or clouds!
Airconditioning is a must for the Summer months. Temperatures in the evenings often don't drop much. If you don't have aircon it can be hard to sleep on those balmy nights especially if you are not used to the heat and humidity.
Autumn - Mar to May
Autumn is still warm to hot during the days and slightly cooler at nights. Humidity drops and there is less rain. Autumn in the Gold Coast is similar to Spring - it's a great time to visit.
Winter - Jun to Aug
Winter in the Gold Coast is awesome. Clear blue skies and warm days. Crisper evenings and early mornings. Lower humidity.
Coming from the UK originally, I find Winters on the Gold Coast are similar to a reasonable British Summer - and far more predictable!
This is the only time of the year that you are likely need a jumper or jacket in the evenings or if it is windy during the day.
When choosing accomodation for the Winter months, if you want to use the pool in your accomodation, make sure it is heated otherwise you will be disappointed. Funnily enough, the ocean is often warmer than the non-heated pools at this time of the year.