Seattle is famous for frequent rainfall. Almost all of Seattle's rain falls from October to June. The summer months, including September, are usually mild, sunny, and dry, with low humidity and pleasant temperatures. However, sometimes the rainy season begins early, so it is a good idea to plan for the possibility of rain. It seldom rains hard in Seattle, so many residents make do with a rain hat or small umbrella.
You can expect daily high temperatures of about 72°F / 20°C and low temperatures of about 50°F / 10°C. You will certainly need a jacket in the evening to stay warm.
Before traveling, check the current weather forecast in Fahrenheit or Celsius.
Cherry trees in bloom on the University of Washington campus, March 2002. Gowen Hall, home of the Department of Asian Languages & Literature, is in the background.