July in Mariehamn is the sunniest and the warmest month of the year. In July, the weather in Mariehamn is typically warm. Average daily high temperature in July is about 18 degrees above zero. On average, Mariehamn has 17 sunny, 10 partly cloudy, and 4 rainy days in July. The rains are usually light. July as well as August is considered the most comfortable time to visit Mariehamn.