Although autumn is generally the most dramatically changeable season on the Oregon coast, early autumn seems only a continuation of summer patterns and processes. Indeed, the streams feeding Oregon's estuaries run clear and low then.
Air temperatures remain warm and are sometimes the highest of the year.
Correspondingly, estuarine waters are relatively warm and salty. By the end of autumn, the estuary will have changed considerably. Tributaries will be running colder and might be high and roilly. The estuary's salinity will have decreased, and the saltwater boundary will have migrated seaward. Autumn arrives at the point of autumnal equinox, when the sun crosses the plane of the earth's equator for the second time of the year.