PHOENIX, ARIZ. — September heat has reached some incredible extremes over the years across the United States, with NOAA data showing all-time September high temperature records ranging from a scorching 117 degrees in Phoenix down to a relatively mild 73 degrees in Anchorage.
Phoenix, Las Vegas and the Desert Southwest Hold the Hottest Records
Phoenix holds the hottest all-time September reading among major U.S. cities at 117 degrees, a record set on September 28, 2024. Las Vegas follows closely behind at 114 degrees, recorded on September 6, 2020, while Los Angeles checks in at 110 degrees from a September 26, 1963 heat wave. That trio of desert Southwest cities represents the upper end of what September heat can produce in the hottest corners of the country.
The presence of the Phoenix and Las Vegas records among the most recent entries on this list, both set within the last several years, stands out compared with several other cities whose records date back decades or even more than a century.
Texas Cities Cluster Around the Same Historic September Day
Several Texas and central Plains cities share the exact same record date, September 4, 2000, including Dallas at 111 degrees and Houston at 109 degrees. Oklahoma City set its own record just a day earlier, on September 3, 2000, at 108 degrees. That clustering of records around the same early September window suggests a significant, widespread heat wave gripped the south-central United States during that specific stretch of 2000.
Kansas City holds an even older record from this same general region, reaching 109 degrees on September 3, 1947, showing that intense September heat in this part of the country is not a purely modern phenomenon.
A Shared Heat Wave Struck the East Coast in 1881
Perhaps the most striking pattern in this data involves September 7, 1881, when Boston, Philadelphia and Washington, D.C., all set their all-time September high temperature records on the exact same day. Boston and Philadelphia both reached 102 degrees, while D.C. climbed to 104 degrees, reflecting what must have been an extraordinarily intense and widespread heat wave gripping the entire East Coast corridor that day.
The fact that these records, set nearly a century and a half ago, still stand today underscores just how extreme that particular 1881 heat wave truly was, especially considering how much the climate and urban heat island effects in these cities have changed since then.
Several Records Have Fallen Just in the Last Few Years
A notable number of the September heat records on this list were set surprisingly recently, including Boise and Salt Lake City both reaching their all-time September highs on September 7, 2022, at 104 and 107 degrees respectively. Rapid City and Denver both set their records on September 5, 2020, at 104 and 101 degrees, the same day Tampa recorded its own all-time September high of 96 degrees.
That cluster of records from 2020, 2022 and 2024 stands out against cities whose records date back to the mid-1900s or earlier, highlighting how several parts of the country have experienced their most extreme September heat within just the past few years.
Cooler Corners of the Country: Anchorage and the Pacific Northwest
Not every part of the country shares in these extreme September temperatures. Anchorage, Alaska, holds by far the coolest all-time September high on this list at just 73 degrees, set on September 5, 1957. Seattle and Burlington, Vermont, also sit toward the cooler end of the spectrum, with all-time September highs of 98 degrees each, recorded in 1988 and 2002 respectively.
That contrast between Anchorage’s 73 degree ceiling and Phoenix’s 117 degree record illustrates the enormous range of climate conditions across the country, even when looking at the single hottest day each location has ever recorded during the same calendar month.
What These Records Say About September Heat Potential
Taken together, this collection of all-time September highs shows that the month can produce genuinely extreme heat across a wide swath of the country, from the desert Southwest to the Great Plains to the East Coast. Whether tied to a single historic heat wave shared across multiple cities, like the East Coast’s 1881 event or the south-central United States in 2000, or a more recent, isolated record like Phoenix’s 2024 reading, September has repeatedly proven capable of delivering temperatures that rival or exceed what many people associate with the heart of summer.
