nomadseason

September Weather in Portland, United States

Last updated: June 24, 2025

In Portland, United States, the average temperature in September hovers around 23°C (74°F). Expect a range, with minimum temperatures dipping to 8°C (47°F) and maximums soaring to 36°C (97°F). This month also brings 125 mm (4.9 in) of precipitation over approximately 8 days, contributing to an average humidity level of 71%.

September Temperature in Portland

In September in Portland, the average temperature is 23°C (74°F). The maximum can reach 36°C (97°F) and the minimum can be as low as 8°C (47°F). This makes it an ideal destination for travelers seeking warm weather, but be prepared for 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 23°C (74°F), with highs reaching up to 36°C (97°F) and lows dropping to around 8°C (47°F).
JanFebMarAprMayJunJulAugSepOctNovDec404452597076807873634845
Data source: Temperature data for Portland generated using information from the Copernicus Climate Change Service.
Choose your preferred temperature unit
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 125 mm (4.9 in) over the course of 8 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 125 mm (4.9 inches) of precipitation spread over approximately 8 days.
JanFebMarAprMayJunJulAugSepOctNovDec10518515715012214112512412513888147
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
Choose your preferred precipitation unit

September Humidity in Portland

In Portland in September, humidity is 71%. With an average temperature of 23°C (74°F), this humidity feels like a warm, enveloping embrace that can make outdoor activities feel sticky, but if you're well-hydrated and take breaks in the shade, it offers a pleasant tropical ambiance perfect for exploration.

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 71%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec87%86%86%82%83%83%80%74%71%78%88%88%
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 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 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 9, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec36710101111109753
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 Weather4°C (40°F)105 mm (4.1 inches)87%moderate
February Weather7°C (44°F)185 mm (7.3 inches)86%high
March Weather11°C (52°F)157 mm (6.2 inches)86%high
April Weather15°C (59°F)150 mm (5.9 inches)82%very high
May Weather21°C (70°F)122 mm (4.8 inches)82%very high
June Weather25°C (77°F)141 mm (5.5 inches)83%extreme
July Weather27°C (80°F)125 mm (4.9 inches)80%extreme
August Weather25°C (78°F)124 mm (4.9 inches)74%very high
September Weather23°C (74°F)125 mm (4.9 inches)71%very high
October Weather17°C (63°F)138 mm (5.4 inches)78%high
November Weather9°C (48°F)88 mm (3.4 inches)88%moderate
December Weather7°C (45°F)147 mm (5.8 inches)88%moderate

Compare Portland's Climate with Cities Worldwide