DC’s hot start to September

 

A warm day in the nation's capital

The nation’s capital had a memorable start to September with highs in the 90s on the first four days of the month, which hasn’t happened since 2015. That’s not surprising since the meteorological summer (June, July and August) that just ended finished as DC’s eighth warmest on record. Nine of DC’s 10 warmest summers have now occurred in the last two decades. 

This summer’s most extreme heat occurred in early July when the nation’s capital experienced it’s warmest July 4 with a record high of 103°. Triple-digit heat also occurred on June 12. The nation’s capital has also experienced summer’s that rank among DC’s Top 10 warmest without any triple-digit heat such as in 2019, 2020 and 2021. 

What’s helped make recent summers hotter in the nation’s capital has been an increased urban heat island effect. Increased greenhouse gas emissions have also contributed to a changing climate that’s made recent summers hotter. According to a recent study by Climate Central, “…human-caused climate change was the leading cause of summer warming — accounting for at least 50% of observed warming since 1970.”

While triple-digit heat is unusual in the nation’s capital and often a sign of a very hot summer, that isn’t always the case. For example, the nation’s capital experienced a total of five days of triple-digit heat during the summer of 1997, but the summer finished nearly two degrees below average. That helps illustrate that a few hot days aren’t enough to produce a warmer than average season.

On the other hand, a very hot summer can sometimes linger into September. Longtime Washingtonians might remember the summer of 1980. The nation’s capital experienced triple-digit heat in July, August and September of 1980. DC’s record high of 101° on September 2, 1980, was one of only four days the nation’s capital has experienced triple-digit September heat and the most recent.

Not only was September 1980 DC’s second warmest on record, but was warmer than June 1980. DC’s warmest September in 1881 was the warmest month of the entire year. Although no triple-digit heat occurred or is likely to occur in the nation’s capital this September, NOAA’s Climate Prediction Center expects this month to be warmer than average. 

DC’s warmest September’s (NOAA)

1. 78.2° - 1881 (hottest month of year)
2. 77.1° - 1980 (warmer than June)
3. 76.5° - 2019 (warmer than June)
4. 76.0° - 2016, 1930
5. 75.5° - 2018, 2010
6. 75.4° - 1998 (warmer than June)
7. 75.0° - 2005, 1970
8. 74.9° - 2015
9. 74.8° - 1961 (warmer than June)
10. 74.4° - 1921 (warmer than June, August)

 

DC’s hottest summers (NOAA)

1. 81.3° - 2010
2. 81.1° - 2011 (triple-digit heat in all 3 months)
3. 80.9° - 2024 (all 3 months)
4. 80.5° - 2016
5. 80.4° - 2012
6. 80.2° - 2020 (no triple-digit heat)
7. 80.0° - 1980 (July, August, September)
8. 79.8° - 2026
9. 79.5° - 2021, 2019 (no triple-digit heat in either year)
10. 79.4° - 2002, 1991