 According to the United States Census Bureau, the city has a total area of , of which, is land and is water.This region experiences warm (but not hot) and relatively dry summers, with no average monthly temperatures above and very wet autumns and springs due to the maritime winds.According to the Köppen Climate Classification system, Montesano is in a region of oceanic climate, abbreviated "Cfb" on climate maps due to frequent summer rainfall, even though there is a significant drying trend during that season.