August in Bilbao is the warmest month of the year. In August, the weather in Bilbao is typically warm. Average daily high temperature in August is about 22 degrees above zero. On average, Bilbao has 16 partly cloudy, 11 sunny, and 4 rainy days in August. The rains are usually light. August as well as September is considered the most comfortable time to visit Bilbao.