In terms of precipitation, rainfall in Mariehamn ranges from 0.8 - 2.8 inches per month. August is typically the wettest month, when rainfall can reach 2.8 in. February is typically the driest time to visit Mariehamn when rainfall is around 0.8 in.
If weather is an important factor for your trip to Mariehamn, use this chart to help with planning. For those seeking warmer temperatures, July is the ideal time of year to visit, when temperatures reach an average of 59.0 F. Travelers looking to avoid the cold should look outside of February, when temperatures are typically at their lowest (around 26.6 F).