Fall had already arrived on the calendar, but across much of the United States, the heat had not received the message.
September 2026 became the warmest September ever recorded for the contiguous United States, according to the National Oceanic and Atmospheric Administration, turning what is normally a transition month into another striking entry in the country's temperature record.
The national average temperature reached 69.4°F, which was 4.6°F above the 20th-century average and higher than the previous September record of 68.95°F, set in 1998. Eight states recorded their warmest September on record, with Arkansas, Illinois, Kansas, Missouri and Oklahoma breaking records that dated back to the 1920s or 1930s.
For anyone accustomed to the familiar rhythm of American seasons, the number raises a natural question.
Was September simply an unusually hot month, or is it part of something larger?
The calendar said fall. The thermometer told another story.
September is supposed to be a month of transition. Summer begins giving way to cooler mornings, shorter days and, eventually, the changing leaves that signal autumn across much of the country.
But NOAA's latest figures show just how unusual September 2026 was. The contiguous U.S. average temperature was not merely above normal; it surpassed the previous September record by nearly half a degree Fahrenheit.
That national number also hides some striking regional differences.
Large portions of the southern and central Plains and the Mississippi Valley experienced record warmth, while parts of northern California and the Pacific Northwest were actually cooler than average. A national record, therefore, does not mean every American experienced the same kind of September.
Still, the broader pattern is difficult to miss.
September was the fourth month in 2026 to set a monthly temperature record for the contiguous United States, following March, July and August. NOAA also found that the country's monthly average temperature had remained above its respective 20th-century average for 20 consecutive months, from February 2025 through September 2026.
Eight states had their warmest September ever
The national record becomes even more striking when viewed state by state.
Arkansas, Illinois, Kansas, Missouri and Oklahoma all surpassed September temperature records that had stood since the early decades of the 20th century. Four additional states also recorded their warmest September, according to NOAA.
For residents in those states, the record was not something happening somewhere far away.
It was the weather outside the window.
Yet even here, there is an important scientific distinction. A record temperature in one state or one month does not establish the cause of that particular event by itself.
Climate scientists look for patterns that persist across much longer periods.
And then there was the rain
September's story becomes even more complicated when precipitation enters the picture.
While the country experienced its warmest September on record, average precipitation across the contiguous United States was also above the 20th-century average, placing the month in the wettest third of the historical record. The Southwest stood out in particular, with Arizona and New Mexico experiencing exceptionally wet conditions.
Arizona received 2.97 inches of precipitation, about 252% of its average, making it the state's wettest September since 1983. New Mexico received more than five inches, about 304% of average, making it the state's wettest September since 1941.
That may sound contradictory.
How can a month be exceptionally hot while parts of the same country are also experiencing extraordinary rainfall?
The answer is that temperature and precipitation are different parts of the climate system. A warmer climate does not mean every place simply becomes hotter and wetter at the same time, and individual rainfall events depend on atmospheric circulation, moisture, geography and other factors.
That complexity is exactly why scientists avoid drawing conclusions from a single weather event.
El Niño is part of the picture
There is another piece to September's global climate story: El Niño.
NOAA reported that persistent El Niño conditions were driving record warmth in the central and eastern tropical Pacific and contributing significantly to elevated global ocean temperatures. Globally, September 2026 ranked as the second-warmest September on record, behind September 2023.
El Niño is a naturally occurring climate pattern that can influence weather and temperatures around the world.
Its presence does not mean every record set during the month can be attributed to El Niño, nor does it erase the longer-term warming trend. Instead, it is one of the natural factors scientists consider when trying to understand why a particular period was warmer or cooler than expected.
What happens when fall begins to feel different?
For many Americans, autumn is more than a date on the calendar.
It is the first cool morning after summer, the return of jackets to closets, football weekends, changing leaves, apple orchards and evenings when the air finally feels crisp again. Those experiences are tied to the natural rhythms of temperature, daylight and precipitation that help give each season its identity.
A warmer September does not mean those traditions are disappearing.
But repeated changes in seasonal temperatures can alter how and when people experience them.
That is where a climate statistic begins to feel less distant. A record temperature on a NOAA chart can eventually become a longer summer evening, a later cool-down, a different fall landscape or another month of running the air conditioner.
What Happens Next
October has already begun, but September's record will remain part of the U.S. climate record long after the leaves have fallen.
NOAA's outlook favors above-average temperatures across much of the West and northern Plains, as well as along the Gulf Coast and Florida, while drought is expected to persist in parts of the West and northern High Plains.
Whether October follows September's warmth everywhere is impossible to know from the September record alone.
What can be measured is the longer pattern.
Fall will still arrive. Leaves will still change, football stadiums will still fill and families will still gather for the traditions that make autumn feel like autumn.
But if the seasons people recognize begin arriving with different temperatures and different weather patterns, one question becomes increasingly relevant: how will we recognize the seasons we grew up knowing in a climate that is changing?
