September Weather in Portland, United States

Last updated: June 24, 2025

In Portland, United States, the average temperature in September hovers around 18°C (64°F). Expect minimums as low as 3°C (37°F) and highs reaching up to 33°C (92°F). Rainfall averages 111 mm (4.4 in) spread over about 10 days, contributing to an average humidity of 74%. Stay prepared for a mix of pleasant warmth and occasional showers!

September Temperature in Portland

In September in Portland, the average temperature is 18°C (64°F). Maximum temperatures can reach 33°C (92°F), while minimums can drop as low as 3°C (37°F). Be sure to pack layers and plan for a variety of weather conditions during your travels!

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

The chart illustrates September temperature patterns in Portland, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Portland, September typically has an average temperature of 18°C (64°F), with highs reaching up to 33°C (92°F) and lows dropping to around 3°C (37°F).

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

September Precipitation in Portland

In Portland in September, the precipitation amount is 111 mm (4.4 in) over a span of 10 days.

September Precipitation Trends in Portland

The chart displays monthly precipitation patterns in Portland, 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 Portland, September typically receives around 111 mm (4.4 inches) of precipitation spread over approximately 10 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 Portland

In Portland in September humidity is 74%. With an average temperature of 18°C (64°F), this humidity feels like a warm embrace, making it ideal for leisurely strolls but potentially uncomfortable for extended outdoor activities.

September Average Humidity in Portland

This chart illustrates the average monthly humidity levels in Portland, 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 Portland is approximately 74%, 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 Portland

In Portland in September, the maximum UV index is 8, which corresponds to a very high Exposure Category. This means that the time to burn is only 15 minutes. For more detailed information, you can refer to the Hourly UV Index in Portland.

Maximum UV Index Levels in Portland for September

The chart shows the monthly maximum UV Index (UVI) for Portland 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 Portland typically reaches 8, which falls under the very high exposure category.

Data source: Portland 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 Portland Compares to Other Months

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

This table compares monthly weather conditions in Portland, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
	Temperature	Precipitation	Humidity	UV
January Weather	-7°C (20°F)	38 mm (1.5 inches)	84%	low
February Weather	-6°C (21°F)	54 mm (2.1 inches)	85%	moderate
March Weather	2°C (35°F)	60 mm (2.3 inches)	84%	moderate
April Weather	7°C (45°F)	92 mm (3.6 inches)	83%	very high
May Weather	15°C (59°F)	139 mm (5.5 inches)	75%	very high
June Weather	21°C (70°F)	124 mm (4.9 inches)	79%	very high
July Weather	23°C (74°F)	112 mm (4.4 inches)	75%	very high
August Weather	21°C (70°F)	112 mm (4.4 inches)	69%	very high
September Weather	18°C (64°F)	111 mm (4.4 inches)	74%	very high
October Weather	10°C (50°F)	119 mm (4.7 inches)	79%	moderate
November Weather	1°C (35°F)	53 mm (2.1 inches)	88%	moderate
December Weather	-3°C (27°F)	44 mm (1.7 inches)	82%	low