Adelaide: Annual Weather Averages. January is the hottest month in Adelaide with an average temperature of 23°C (73°F) and the coldest is July at 11°C (52°F) with the most daily sunshine hours at 10 in February.The wettest month is July with an average of 70mm of rain.delaide: Annual Weather Averages. January is the hottest month in Adelaide with an average temperature of 23°C (73°F) and the coldest is July at 11°C (52°F) with the most daily sunshine hours at 10 in February.