A month ago we reported that the US had just finished its warmest summer on record. The obvious question was whether the heat would ease with the season. NOAA's September report answers it: it didn't.
The figures
September 2026 averaged 69.4°F across the contiguous United States, 4.6°F above the twentieth-century average, the warmest September in the 1895–present record.
The previous record was 68.95°F, set in 1998. September beat it by nearly half a degree, the same kind of margin the summer record had. As we noted then, national records usually fall by hundredths of a degree, because averaging a whole month across a whole continent cancels out most of the weather. Two margins that size in a row are unusual.
September also extended a streak. The Lower 48 has now run warmer than its twentieth-century average for 20 consecutive months, every month since February 2025.
Where it was hottest
The heat was centered on the middle of the country. Eight states had their warmest September on record. In five of them, Arkansas, Illinois, Kansas, Missouri and Oklahoma, the record they broke dated to the 1920s or 1930s, the same era as the 1936 summer that held the national record until this year.
Not everywhere was hot. Small parts of northern California and the Pacific Northwest ran cooler than average, a reminder that a national record is an average of very different places.
The rain went to the wrong places
Nationally, September was slightly wet: 2.69 inches of precipitation, 0.20 inch above average. That number hides an uneven month.
The Southwest got soaked. Arizona had its wettest September since 1983, at about two and a half times its normal total, and New Mexico its wettest since 1941, at roughly three times normal.
The South Central states, where the heat was worst, got far less help. As of September 29, about 59 percent of the contiguous US was in drought. In NOAA's South region, which runs from Kansas and Oklahoma through Texas to the lower Mississippi, 89 percent of the land was in drought, the largest share there since October 2000. That is the pattern we described in September, when drought had spread across most of the Lower 48: heat raises evaporation, so the same rainfall goes less far, and a month with no rain to spare turns into a drought that keeps growing.
What it does and doesn't tell us
A single record month is weather. What makes this one worth reporting is the context around it:
- The margin. The summer record and now September's both fell by close to half a degree.
- The streak. Twenty months in a row above the long-term average.
- The geography. State records nearly a century old are falling across the Plains and the mid-Mississippi Valley.
Each of those is consistent with what long-term warming predicts: a higher baseline, so ordinary hot spells push further past old records.
The next few months have a dominant driver of their own. We wrote last week that NOAA gives the current El Nino a 75 percent chance of reaching historic strength this autumn. A strong El Nino typically means a wetter winter across the southern US and a milder one across the north. For the drought-stricken South, a wet winter would help. It would not undo a year of heat.
Follow the numbers
National records describe the problem. Our data dashboard tracks the local side of the response: the tree canopy, solar output and emissions reductions from our own programs. We will report October's national numbers when NOAA publishes them, whichever way they go.
