August in Arcachon is the warmest month of the year. In August, the weather in Arcachon is typically warm. Average daily high temperature in August is about 23 degrees above zero. On average, Arcachon has 20 sunny, 9 partly cloudy, and 2 rainy days in August. The rains are usually light. August as well as July is considered the most comfortable time to visit Arcachon.