Last updated: June 24, 2025
In Portland, United States, the average temperature in September is a pleasant 19°C (67°F), with minimums dipping to 3°C (38°F) and maximums soaring up to 33°C (91°F). Expect around 107 mm (4.2 in) of precipitation spread over 9 days, contributing to an average humidity of 66%. Whether you're enjoying the warm days or cool evenings, there's a comfortable balance to the climate this month!
In September in Portland, the average temperature is 19°C (67°F). Maximums can reach 33°C (91°F), and minimums can be as low as 3°C (38°F). This makes Portland a great destination for travelers seeking mild weather and a chance to enjoy a variety of outdoor activities.
In Portland in September, the precipitation amount is 107 mm (4.2 in), occurring over a span of 9 days.
In Portland in September humidity is 66%. With an average temperature of 19°C (67°F), this humidity feels like a warm blanket wrapping around you, making it mildly uncomfortable for traveling, as you may find yourself needing to frequently stop for hydration and to seek shade from the sun.
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 | -1°C (31°F) | 71 mm (2.8 inches) | 87% | moderate |
| February Weather | 1°C (34°F) | 102 mm (4.0 inches) | 85% | moderate |
| March Weather | 4°C (39°F) | 94 mm (3.7 inches) | 85% | high |
| April Weather | 10°C (50°F) | 110 mm (4.3 inches) | 83% | very high |
| May Weather | 16°C (61°F) | 135 mm (5.3 inches) | 75% | very high |
| June Weather | 21°C (69°F) | 92 mm (3.6 inches) | 73% | very high |
| July Weather | 24°C (75°F) | 124 mm (4.9 inches) | 65% | very high |
| August Weather | 23°C (73°F) | 125 mm (4.9 inches) | 62% | very high |
| September Weather | 19°C (67°F) | 107 mm (4.2 inches) | 66% | very high |
| October Weather | 14°C (57°F) | 141 mm (5.5 inches) | 79% | high |
| November Weather | 6°C (42°F) | 90 mm (3.5 inches) | 87% | moderate |
| December Weather | 2°C (35°F) | 106 mm (4.2 inches) | 85% | low |