Last updated: June 24, 2025
In September, the average temperature in Portland, United States hovers around 20°C (69°F). You can expect a minimum of 4°C (39°F) and a maximum of 33°C (91°F), creating a diverse climate. Prepare for 75 mm (2.9 in) of precipitation spread over approximately 8 days, and be ready for a moist atmosphere with an average humidity of 78%.
In September in Portland, the average temperature is 20°C (69°F). The maximum can reach 33°C (91°F), while the minimum can drop as low as 4°C (39°F). This variation in temperature makes Portland a versatile destination for travelers seeking both warm days and cool evenings.
In Portland in September, the precipitation amount is 75 mm (2.9 in) over a span of 8 days.
In Portland in September, humidity is 78%. With an average temperature of 20°C (69°F), this humidity feels like a warm, enveloping blanket, making travel somewhat uncomfortable as sweat clings to your skin and the air feels thick and heavy, urging you to seek out shaded areas and refreshing drinks.
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.
UV Risk Categories
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.
| Temperature | Precipitation | Humidity | UV | |
|---|---|---|---|---|
| January Weather | -2°C (29°F) | 74 mm (2.9 inches) | 85% | moderate |
| February Weather | 0°C (32°F) | 88 mm (3.4 inches) | 85% | moderate |
| March Weather | 5°C (42°F) | 101 mm (4.0 inches) | 86% | high |
| April Weather | 10°C (51°F) | 93 mm (3.7 inches) | 87% | very high |
| May Weather | 17°C (63°F) | 127 mm (5.0 inches) | 81% | very high |
| June Weather | 22°C (73°F) | 114 mm (4.5 inches) | 82% | extreme |
| July Weather | 24°C (76°F) | 101 mm (4.0 inches) | 81% | very high |
| August Weather | 23°C (74°F) | 102 mm (4.0 inches) | 79% | very high |
| September Weather | 20°C (69°F) | 75 mm (2.9 inches) | 78% | very high |
| October Weather | 14°C (57°F) | 97 mm (3.8 inches) | 81% | high |
| November Weather | 5°C (42°F) | 82 mm (3.2 inches) | 89% | moderate |
| December Weather | 2°C (35°F) | 67 mm (2.7 inches) | 86% | low |