The climate of Eureka is completely maritime with high humidity prevailing throughout the year. There are definite rainy and dry seasons. The rainy season lasts from October through April accounting for about 90 percent of the annual precipitation. The dry season, lasting from May through September, is typically marked by regular intrusions of low clouds and fog which usually clear by late morning.
Early afternoon is generally mostly sunny with the low clouds moving back in by evening.
Temperatures are quite moderate, and the annual range is one of the smallest in the lower 48 states. During a typical year, the colder lows are in the mid 30s and the warmer highs will reach the mid 70s. The reason for the small temperature range is the close proximity of Eureka to the Pacific ocean. The prevailing northwest wind blows across the cold up-welling water that is almost always present along the along the Humboldt County coast. While the immediate coast is largely affected by the cold Pacific ocean, locations inland can have a much greater range of temperature.