Monthly Attribution Overview – September 2025

The analysis shows that 161 of 192 analyzed U.S. cities experienced hotter-than-average temperatures in September 2025, with an average anomaly of 1.5°F. The Northwest region saw the most unusual heat, averaging 3.42°F above normal, while Spokane, WA, recorded the highest individual city anomaly at 7.8°F. Long-term trends indicate widespread warming since 1970, with Reno, NV, showing the fastest increase at 10.8°F. Climate Shift Index (CSI) data highlighted strong climate change influence in several cities, most notably San Juan, PR, which had 22 days at CSI 5.

• In September 2025, the average temperature anomaly across 192 analyzed U.S. cities was 1.5°F, with 161 cities recording hotter-than-average temperatures.
• The Northwest region, including Washington, Oregon, and Idaho, experienced the most unusual heat with an average temperature anomaly of 3.42°F, while Spokane, WA, was the most unusually warm city at 7.8°F above usual.
• Long-term data since 1970 shows warming trends in 190 of the 191 ACIS stations analyzed, with Reno, NV, experiencing the most significant increase of 10.8°F.
• Climate Shift Index (CSI) values indicated a strong climate change influence in several locations; San Juan, PR, recorded 22 days at CSI 5, meaning temperatures were at least five times more likely due to climate change.

APA

Climate Central (2025). Monthly Attribution Overview – September 2025. https://www.climatecentral.org/report/monthly-attribution-overview-september-2025

Chicago

Climate Central. Monthly Attribution Overview – September 2025. 2025. https://www.climatecentral.org/report/monthly-attribution-overview-september-2025.

Wikipedia

{{cite report |author=Climate Central |title=Monthly Attribution Overview – September 2025 |date=9 October 2025 |url=https://www.climatecentral.org/report/monthly-attribution-overview-september-2025 |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{climatecentral2025monthly, author = {{Climate Central}}, title = {{Monthly Attribution Overview – September 2025}}, institution = {Climate Central}, year = {2025}, month = oct, url = {https://www.climatecentral.org/report/monthly-attribution-overview-september-2025}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }