September is often one of Washington’s most pleasant months, known for abundant sunshine and stretches of blue-sky days. But it also coincides with the peak of hurricane season, when tropical systems can bring bouts of heavy rain, flooding and even severe weather, including tornadoes.
Normal and record daily temperatures
September begins with average highs near 85 degrees and lows around 69 degrees, but by month’s end those fall to about 75 and 59 degrees, respectively.
The overall average temperature of 72.4 degrees is the same as July’s average low, underscoring how noticeable the transition toward fall becomes over the course of the month.
Extremes can still occur. The hottest September temperature on record is 104 degrees, set in 1881, while the coldest reading is 36 degrees, observed in 1904.
In other words, September often feels like summer at the start and fall by the finish.
Record daily precipitation
September can be a bit of a mixed bag for precipitation. While summer humidity begins to ease, the peak of hurricane season often brings heavy rain — either from nearby tropical systems or moisture streaming north from storms offshore.
The wettest September day on record in Washington brought 5.16 inches on Sept. 1, 1922. Even the lowest daily record for the month exceeds 1 inch, set on Sept. 19, 1875.
Monthly temperatures by the year
In a rarity for D.C.’s warming climate, the warmest September on record occurred long ago. The top spot belongs to 1881, with an average temperature of 78.2 degrees. The coolest September came in 1917, averaging 63.9 degrees.
Even so, September temperatures have risen over time, with the monthly average increasing by about 4 degrees since 1900.
Monthly precipitation by the year
September 1934 stands far above the rest, with an astounding 17.45 inches of rain — the wettest September on record and the wettest month of any kind in Washington.
That month featured six days with more than an inch of rain and 15 days with measurable precipitation, underscoring just how persistently wet it was.
Overall, September’s precipitation has remained relatively steady over time, with only modest year-to-year variability.
Days at or above 90
September typically marks the end of the 90-degree season, which runs from mid-May through mid-September. In the current climate, the average final 90-degree day occurs around Sept. 11.
The month still averages three to four 90-degree days before the heat fades. The most on record is 14 days, set in 1980, while many years see none at all.
Peak tropical season
With average highs falling from about 85 to 75 degrees during September, “nice days” — dry, calm and comfortably warm — are fairly common.
But September also marks the peak of hurricane season, and tropical systems remain a regular threat.
Numerous storms or their remnants have passed near or directly through the region, often bringing heavy rain, flooding and occasional tornadoes. Hurricane Ivan (2004) and Hurricane Isabel (2003) stand out as recent examples — the former for its tornado outbreak and the latter for its historic storm surge and widespread tree damage.
Events of note
Sept. 1, 1922. The wettest September day on record, with 5.16 inches of rain, including 2.38 inches in one hour.
Sept. 4, 1939. A slow-moving storm dropped 4.49 inches of rain, leaving more than 100 cars stalled in floodwaters across the city.
Sept. 4–5, 1935. 7.09 inches of rain fell, including 4.45 inches on the 5th, from the remnants of the historic Labor Day hurricane. More than a foot of rain fell in southern Maryland, where tornadoes also occurred.
Sept. 7, 1881. The hottest September day on record, with a high of 104 degrees.
Sept. 8, 2011. Flooding from the remnants of Tropical Storm Lee killed three people and trapped motorists across the region.
Sept. 16, 1888. A tornado struck the southern edge of downtown and tracked about 2 miles toward Capitol Hill.
Sept. 17, 2004. Tornadoes spawned by the remnants of Hurricane Ivan struck the region, mainly impacting western and southern suburbs. The event became Virginia’s largest tornado outbreak on record.
Sept. 18, 2003. After making landfall as a Category 2 hurricane, Isabel swept through the region, causing major storm surge flooding on the Potomac River and Chesapeake Bay, including in Annapolis.
Sept. 24, 2001. An F3 tornado struck College Park, killing two students. Several tornadoes occurred across the region that day.
