September Weather in Washington, United States

Last updated: June 24, 2025

In Washington, United States, the average temperature in September hovers around 25°C (77°F), providing a warm and inviting climate. However, be prepared for temperature fluctuations, as the minimum can dip to 11°C (52°F), while the maximum may reach a sweltering 36°C (98°F). Expect about 98 mm (3.9 in) of precipitation over 8 days, with a notable average humidity level of 82%. Perfect for those who enjoy a humid, tropical feel!

September Temperature in Washington

In September in Washington, the average temperature is 25°C (77°F). Maximum temperatures can reach 36°C (98°F), while minimums can dip as low as 11°C (52°F). Overall, it is a great time to visit Washington for warm weather adventures while being prepared for cooler evenings.

September Weather in Washington: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Washington, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Washington, September typically has an average temperature of 25°C (77°F), with highs reaching up to 36°C (98°F) and lows dropping to around 11°C (52°F).

Data source: Temperature data for Washington generated using information from the Copernicus Climate Change Service.

September Precipitation in Washington

In Washington in September, the total precipitation amount is 98 mm (3.9 in), occurring over 8 days.

September Precipitation Trends in Washington

The chart displays monthly precipitation patterns in Washington, with values for each month alongside September’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how September’s conditions compare to those of other months. In Washington, September typically receives around 98 mm (3.9 inches) of precipitation spread over approximately 8 days.

Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.

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Millimeters (mm) Inches (in)

September Humidity in Washington

In Washington in September, humidity is 82%. With an average temperature of 25°C (77°F), this humidity feels like a warm, oppressive blanket enveloping you as you explore, making every step feel more laborious and prompting the need for frequent hydration breaks.

September Average Humidity in Washington

This chart illustrates the average monthly humidity levels in Washington, with September’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In September, average humidity in Washington is approximately 82%, offering insight into how humid the weather typically is during this month.

Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Washington

In Washington in September, the maximum UV index is 9, which corresponds to a very high Exposure Category. The time to burn is just 15 minutes, so it's essential to take precautions. For detailed information, you can check the Hourly UV Index in Washington.

Maximum UV Index Levels in Washington for September

The chart shows the monthly maximum UV Index (UVI) for Washington in September, representing the highest UV radiation level. The UVI measures the intensity of ultraviolet radiation from the sun, indicating the potential risk of sunburn and UV-related health issues. In September, the maximum UV index in Washington typically reaches 9, which falls under the very high exposure category.

Data source: Washington September UVI data generated using information from the Copernicus Climate Change Service.

UV Risk Categories

Extreme (11+): Avoid the sun, stay in shade.
Very High (8-10): Limit sun exposure.
High (6-7): Use SPF 30+ and protective clothing.
Moderate (3-5): Midday shade recommended.
Low (0-2): No protection needed.

How September Weather in Washington Compares to Other Months

Weather in Washington varies notably across the year, with each month offering distinct climate conditions. This page compares September’s weather to other months in Washington, focusing on differences in temperature, rainfall, humidity, and UV levels.

This table compares monthly weather conditions in Washington, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
	Temperature	Precipitation	Humidity	UV
January Weather	9°C (48°F)	100 mm (3.9 inches)	86%	moderate
February Weather	12°C (53°F)	117 mm (4.6 inches)	84%	high
March Weather	14°C (58°F)	87 mm (3.4 inches)	83%	very high
April Weather	18°C (65°F)	107 mm (4.2 inches)	81%	very high
May Weather	23°C (73°F)	109 mm (4.3 inches)	81%	extreme
June Weather	26°C (79°F)	97 mm (3.8 inches)	81%	extreme
July Weather	27°C (82°F)	105 mm (4.1 inches)	83%	extreme
August Weather	27°C (81°F)	125 mm (4.9 inches)	81%	very high
September Weather	25°C (77°F)	98 mm (3.9 inches)	82%	very high
October Weather	20°C (68°F)	112 mm (4.4 inches)	78%	very high
November Weather	12°C (54°F)	82 mm (3.2 inches)	86%	high
December Weather	10°C (50°F)	117 mm (4.6 inches)	89%	moderate