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September Weather in Portland, United States

Last updated: June 24, 2025

In September, the average temperature in Portland, United States hovers around 20°C (67°F), making it a pleasant time to visit. However, be prepared for temperature fluctuations, with a minimum of 4°C (40°F) and a maximum of 34°C (93°F). Expect some rainfall, as 99 mm (3.9 in) of precipitation typically falls over 9 days. Additionally, the average humidity level sits at a comfortable 68%, ensuring a refreshing atmosphere throughout the month.

September Temperature in Portland

In September in Portland, the average temperature is 20°C (67°F), with maximums reaching 34°C (93°F) and minimums dropping as low as 4°C (40°F). This range makes Portland an ideal destination for travelers seeking pleasant weather and the versatility to enjoy both warm days and cooler evenings.

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 20°C (67°F), with highs reaching up to 34°C (93°F) and lows dropping to around 4°C (40°F).
JanFebMarAprMayJunJulAugSepOctNovDec323439495969757467574436
Data source: Temperature data for Portland generated using information from the Copernicus Climate Change Service.
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The average of daily temperatures (24 hours) calculated across all days in the month.

September Precipitation in Portland

In Portland in September, the precipitation amount is 99 mm (3.9 in) during a span of 9 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 99 mm (3.9 inches) of precipitation spread over approximately 9 days.
JanFebMarAprMayJunJulAugSepOctNovDec67909012611194156969913090127
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Portland

In Portland in September humidity is 68%. With an average temperature of 20°C (67°F), this humidity feels like walking through a warm, heavy blanket, making travel a bit sweltering and causing you to crave frequent breaks in the shade.

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 68%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec84%82%81%78%70%69%62%65%68%74%82%80%
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.
JanFebMarAprMayJunJulAugSepOctNovDec35681010998642
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.
 TemperaturePrecipitationHumidityUV
January Weather0°C (32°F)67 mm (2.6 inches)84%moderate
February Weather1°C (34°F)89 mm (3.5 inches)82%moderate
March Weather4°C (40°F)90 mm (3.6 inches)81%high
April Weather10°C (49°F)126 mm (5.0 inches)78%very high
May Weather15°C (60°F)111 mm (4.4 inches)69%very high
June Weather20°C (69°F)94 mm (3.7 inches)69%very high
July Weather24°C (75°F)156 mm (6.1 inches)62%very high
August Weather23°C (74°F)96 mm (3.8 inches)65%very high
September Weather20°C (67°F)99 mm (3.9 inches)68%very high
October Weather14°C (58°F)130 mm (5.1 inches)74%high
November Weather7°C (44°F)90 mm (3.6 inches)82%moderate
December Weather2°C (36°F)127 mm (5.0 inches)80%low

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