Washington DC Weather in September
United States · Humid Subtropical climate · Data averaged from 2020-01-01 to 2024-12-31 (5 years)
September in Washington DC sees average temperatures ranging from a low of 16.4°C (61.5°F) to a high of 25.7°C (78.3°F), with a mean of 20.7°C (69.3°F). Compared to the annual average of 14.2°C (57.6°F), this month is 6.5°C warmer than the yearly norm. Precipitation averages 134.0mm, making it approximately 15.0mm wetter than the monthly average of 119.0mm. The city receives an average of 8.9 hours of sunshine per day during September, with relative humidity averaging 74.2%. Wind speeds reach an average maximum of 14.6 km/h. For travelers, this month offers a temperature experience in Washington DC, with wetter-than-average conditions compared to the rest of the year.
There's something about Washington DC in late March when the cherry blossoms peak that turns the political city into something tender. I stood at the Tidal Basin one spring as 3,000 trees bloomed pink against the Jefferson Memorial — the data says peak bloom is usually the last week of March to first week of April, around 15°C. Summer (June-August) is famously brutal: 30°C with 70% humidity, the kind that makes the National Mall feel like a sauna. October is DC's secret weapon: 18°C, golden leaves along the Mall, and the cultural season reopening. Winter is quieter and the museums are empty — a trade-off worth making.
September vs Adjacent Months
| Metric | August | September | October |
|---|---|---|---|
| Mean Temp | 24.5°C (76.1°F) | 20.7°C (69.3°F) | 15.1°C (59.2°F) |
| Rainfall | 218.2mm | 134.0mm | 92.4mm |
| Sunshine | 10.5 hrs | 8.9 hrs | 8.1 hrs |
| Humidity | 76.2% | 74.2% | 74.0% |
| Wind | 13.7 km/h | 14.6 km/h | 15.5 km/h |
| Rainy Days | 20.0 | 14.4 | 12.8 |
Seasonal Context
September falls in Autumn in the Northern Hemisphere. Autumn sees temperatures gradually cooling from summer highs. For travelers visiting Washington DC in September, the data indicates mixed conditions based on the combination of temperature, precipitation, and daylight hours.
Frequently Asked Questions
What is the average temperature in Washington DC in September?
The average temperature in Washington DC during September ranges from 16.4°C (61.5°F) to 25.7°C (78.3°F), with a mean of 20.7°C (69.3°F).
How much does it rain in Washington DC in September?
Washington DC receives an average of 134.0mm of precipitation in September, spread across approximately 14.4 rainy days.
What should I pack for Washington DC in September?
Based on September weather data, pack layers including light jackets and t-shirts, plus an umbrella. Rain gear is essential — this month averages 134.0mm of precipitation.
Is September a good time to visit Washington DC?
September is a month with challenging conditions. Plan activities carefully and stay hydrated.
Other Months for Washington DC
Cities with Similar September Climate (Humid Subtropical)
Data Source: Open-Meteo historical archive (2020-01-01 to 2024-12-31). Daily measurements aggregated into monthly climate normals. Coordinates: 38.9°, -77.04°. Timezone: America/New_York. Last updated: 2026-07-30.