Other facts from our historical weather data: Which months have the greatest rainfall in Arcata? Most rainfall (rainy season) is seen in January, March and December. Does Arcata have a dry season? Yes, the months of July and August are very dry. Which is the warmest month in Arcata? September has an average maximum temperature of 20°C (68°F) and is the warmest month of the year. Which is the coldest month in Arcata? The coldest month is December with an average maximum temperature of 12°C (54°F). Which is the wettest month in Arcata? December tops the wettest month list with 227mm (8.9 in) of rainfall. Which is the driest month in Arcata? August is the driest month with 4mm (0.2 in) of precipitation. No idea where to travel to this year? We have a tool that recommends destinations based on your ideal conditions. Find out where to go with our weather planner.