September weather forecastIssaquah, WA
September
Weather in September
September indicates an impending shift towards cooler temperatures. Despite this hint, it stays fairly warm with the UV index holding steady at 4. Cloud cover increases from 27% in August to 36% in September. Rainfall reemerges as a significant weather element with 0.63" (16mm) recorded—an increase from August's mere 0.28" (7mm). A blend of summer's warmth and autumn's mild coolness, September offers a uniquely pleasant weather moment to Issaquah.Temperature
Issaquah in September experiences a gentle temperature dip, with average high-temperatures reducing from a moderately hot 77°F (25°C) in August to a pleasant 70°F (21.1°C). During September, Issaquah notes a substantial drop from the daytime peak to an average minimum temperature of 48.4°F (9.1°C).Humidity
In September, the average relative humidity is 74%.Rainfall
In Issaquah, in September, during 7.8 rainfall days, 0.63" (16mm) of precipitation is typically accumulated. Throughout the year, in Issaquah, there are 127.4 rainfall days, and 12.52" (318mm) of precipitation is accumulated.Snowfall
In Issaquah, snow does not fall in May through October.Daylight
In September, the average length of the day is 12h and 32min.On the first day of the month, sunrise is at 6:28 am and sunset at 7:47 pm. On the last day of September, sunrise is at 7:06 am and sunset at 6:48 pm PDT.
Sunshine
In Issaquah, the average sunshine in September is 9.1h.UV index
In Issaquah, the average daily maximum UV index in September is 4. A UV Index value of 3 to 5 symbolizes a medium health hazard from unsafe exposure to UV radiation for ordinary individuals.Note: A maximum high daily UV index of 4 during September translates into the following directions:
Take necessary precautions - Defending against sun damage is advocated. Avoiding direct sun during mid-day hours can prevent harmful UV radiation exposure. Opt for tightly woven and loose clothing to enhance protection from the Sun.
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
Average temperature in September
Issaquah, WA
- Average high temperature in September: 70°F
The warmest month (with the highest average high temperature) is August (77°F).
The month with the lowest average high temperature is December (42.3°F).
- Average low temperature in September: 48.4°F
The month with the highest average low temperature is August (51.4°F).
The coldest months (with the lowest average low temperature) are February and December (33.4°F).
Average pressure in September
Issaquah, WA
- Average pressure in September: 30.01"Hg
The month with the highest atmospheric pressure is January (30.1"Hg).
The month with the lowest atmospheric pressure is August (30"Hg).
Average wind speed in September
Issaquah, WA
- Average wind speed in September: 3.7mph
The windiest month (with the highest average wind speed) is January (5.1mph).
The calmest month (with the lowest average wind speed) is August (3.4mph).
Average humidity in September
Issaquah, WA
- Average humidity in September: 74%
The months with the highest relative humidity are January and February (85%).
The month with the lowest relative humidity is July (69%).
Average rainfall in September
Issaquah, WA
- Average rainfall in September: 0.63"
The wettest month (with the highest rainfall) is December (2.01").
The driest month (with the least rainfall) is July (0.24").
Average rainfall days in September
Issaquah, WA
- Average rainfall days in September: 7.8 days
The month with the highest number of rainy days is March (14.8 days).
The month with the least rainy days is August (4.3 days).
Average snowfall in September
Issaquah, WA
- Average snowfall in September: 0"
The month with the highest snowfall is February (0.94").
The months with the least snowfall are May, June, July, August, September and October (0").
Average snowfall days in September
Issaquah, WA
- Average snowfall days in September: 0 days
The month with the highest number of snowfall days is February (2.5 days).
The months with the least snowfall days are May, June, July, August, September and October (0 days).
Average daylight in September /
Average sunshine in September
Issaquah, WA
- Average daylight in September: 12h and 30min
The month with the longest days is June (Average daylight: 15h and 54min).
The month with the shortest days is December (Average daylight: 8h and 30min).
- Average sunshine in September: 9h and 6min
The month with the most sunshine is August (Average sunshine: 10h and 30min).
The month with the least sunshine is December (Average sunshine: 4h and 0min).
Average sunshine days in September
Issaquah, WA
- Average sunshine days in September: 19 days
The month with the most sunshine days is August (25 days).
The month with the least sunshine days is February (12.9 days).
Average UV index in September
Issaquah, WA
- Average UV index in September: 4
The month with the highest UV index is July (UV index 5).
The months with the lowest UV index are January, February, November and December (UV index 2).
Average cloud cover in September
Issaquah, WA
- Average cloud cover in September: 36
The months with the most cloud cover are January and December (Cloud cover 58).
The month with the least cloud cover is August (Cloud cover 27).
Average visibility in September
Issaquah, WA
- Average visibility in September: 5mi
The months with the highest visibility are July and August (6mi).
The months with the lowest visibility are January, February and December (4mi).
