Mercer Island Weather in September

September in Mercer Island typically sees daytime highs of 22°C (72°F) and nighttime lows of 12°C (54°F). Expect some rainfall during the month. It falls within the summer season.

Rainfall in Mercer Island in September

Typically around 10 days of rainfall are expected, averaging 52 mm (2 in) for the month. Expect a fairly normal spread of rainfall this month, with no particular pattern of very heavy or very persistent showers.

Temperature in Mercer Island in September

September tends to be one of the excellent months in Mercer Island, with 22°C (72°F) in the afternoon and 12°C (54°F) overnight. Summer occurs in September. Temperatures can feel cooler in the morning and evening, so layering is often the best approach. With overnight lows of 12°C (54°F), evenings can feel noticeably cooler than the daytime. An extra layer is a good idea, though the cool air makes for a good night's sleep.

Sunshine in Mercer Island in September

Enjoy a sunny month with about 220 hours of sunshine, the clear skies make Mercer Island even more beautiful.

Wind Speed in Mercer Island in September

Wind speeds average 4 m/s (8 knots) during September. At this speed, expect moderate winds that can raise dust and move small branches. Since this is an average, some days have gentle light winds while others experience stronger breezes that are quite noticeable.

If you favor pleasant temperatures and minimal rainfall, September is one of the best months to visit Mercer Island.