September 2025 was Earth’s third-warmest September in analyses of global weather data going back to 1850, behind only 2023 and 2024, said the European Copernicus Climate Change Service on Oct. 9. The Japan Meteorological Agency also rated September 2025 the third-warmest September on record. While “third warmest” may not sound eye-poppingly impressive, this comes on the heels of an astoundingly warm couple of years that were fueled by a strong El Niño event atop long-term human-caused warming. In fact, as pointed out by weather records expert Maximiliano Herrera, September 2025 was warmer than any September prior to 2023, regardless of El Niño or La Niña status — a pattern seen time and again this year.
Because of the U.S. government shutdown, data from NOAA and NASA will likely be delayed well past their planned Oct. 10 release date.
La Niña conditions are now in place and likely to continue into 2026
A La Niña advisory is now in effect, as the El Niño/Southern Oscillation, or ENSO, has shifted from a neutral state into La Niña conditions, NOAA reported in its October monthly discussion of ENSO. ENSO is a recurring ocean-and-atmosphere pattern that warms and cools the eastern tropical Pacific through El Niño and La Niña events that last from one to three years. To qualify as such a full-fledged event, El Niño or La Niña conditions must persist in both the ocean and atmosphere for at least five consecutive, overlapping three-month periods.
According to NOAA’s October forecast, there is a 78% chance of La Niña conditions prevailing during October – December 2025, and the odds of La Niña are predicted to remain above 50% through December 2025 – February 2026. The September 19 forecast from the Columbia University International Research Institute for Climate and Society also projects that the odds of La Niña conditions will remain at or above 50% through December 2025 – February 2026. There are very early signs in both the NOAA and Columbia long-range outlook that another El Niño event will become increasingly likely by later in 2026. Since El Niño events tend to transfer large amounts of heat from the ocean to the atmosphere, the next round of record-warm monthly and annual global temperatures can be expected to arrive whenever the next El Niño event sets in.
While El Niño events typically last only one year (usually from northern fall to northern spring, as in 2023-24), La Niña events often restrengthen or recur across two or even three years in a row, as was the case from mid-2020 to early 2023. Conditions over the eastern tropical Pacific were cooler than average in 2024-25, briefly entering El Niño territory but not for long enough to qualify as a La Niña episode. Interestingly, it’s possible 2024-25 will qualify retroactively as a La Niña event a decade from now, when the baseline for making that calculation will almost certainly be warmer (2006–2035 versus 1991–2020), as pointed out by Emily Becker in a climate.gov writeup from last April.
Over the last two decades (2005-2024), the peak three months of hurricane season have included five El Niño periods, seven La Niña periods, and eight neutral periods.
Arctic sea ice: 11th-lowest September extent on record
Arctic sea ice in September 2025 had the 11th-lowest September extent in the 47-year satellite record, according to the National Snow and Ice Data Center, or NSIDC. Arctic sea ice reached its annual minimum on September 10, ranking as the joint-10th lowest in the satellite record.
Antarctic sea ice extent in September was the third-lowest in the 47-year satellite record. Only 2023 and 2024 had lower September extents. Antarctic sea ice reached its annual maximum on September 17; this was its third-smallest winter peak extent since satellite records began 47 years ago.
The Northeast Passage along the coast of Russia and the southern route of the Northwest Passage through Canadian waters were open for ice-free navigation as of Sep. 26, according to ice maps from the U.S. National Ice Center. The Oct. 10 update showed one small area of ice starting to obstruct portions of the Northwest Passage, but the Northeast Passage was still open.
Notable global heat and cold marks for September 2025
Maximiliano Herrera documents world temperature extremes in remarkable detail and has provided us with the following information for September. Follow him on Bluesky: @extremetemps.bsky.social
- Hottest temperature in the Northern Hemisphere: 49.8°C (121.6°F) at Shabankareh, Iran, September 10
- Coldest temperature in the Northern Hemisphere: -38.2°C (-36.8°F) at Summit, Greenland, September 27
- Hottest temperature in the Southern Hemisphere: 43.4°C (110.1°F) at Base Jara, Paraguay, September 14
- Coldest temperature in the Southern Hemisphere: -77.7°C (-107.9°F) at Dome Fuji, Antarctica, September 2
Major weather stations in September: 4 all-time heat records, no all-time cold records
Among global stations with a record of at least 40 years, four set, not just tied, an all-time heat record in September; no stations set an all-time cold record:
- Lhokseumawe (Indonesia) max. 36.9°C, September a
- Sendai (Japan) max. 37.4°C, September 2
- Watari (Japan) max. 36.1°C, September 2
- Roosevelt Airport (St. Eustatius, Netherlands territory) max. 34.4°C, September 13: New territorial record high for St Eustatius
Nine all-time national/territorial heat records beaten or tied as of the end of September
- Maldives: 35.8°C (96.4°F) at Hanimadhoo, Feb. 27 (previous record: 35.1°C (95.2°F) at Hanimadhoo, Mar. 24, 2024
- Togo: 44.0°C (111.2°F) at Mango, Mar. 16 and Apr. 5 (tie)
- Turkey: 50.5°C (122.9°F) at Silopi, Jul. 25
- Kosovo: 42.5°C (108.5°F) at Kline, Jul. 25
- Brunei: 39.2°C (102.6°F) at Sukang, Jul. 29; tied again on Aug. 1 at the same location
- Japan: 41.2°C (106.2°F) at Kaibara, Jul. 30; broken again on Aug. 5 with 41.8°C (107.2°F) at Isesaki
- United Arab Emirates: 51.8°C (125.2°F) at Swiehan, Aug. 1 (tie)
- Martinique: 37.0°C (98.6°F) at Le Lamentin, Aug. 22
- St. Eustatius (Netherlands territory): 34.4°C (93.9°F) at Roosevelt Airport, Sep. 13
Fifty-nine additional monthly national/territorial heat records beaten or tied as of the end of September
In addition to the nine all-time national/territorial records set so far in 2025 (plus three nations that beat or tied their record in two separate months), 59 nations or territories have set or tied monthly all-time heat records as of the end of September 2025, for a total of 71 monthly heat records:
- January (6): Cocos Islands. French Southern Territories, Faroe Islands, Maldives, Northern Marianas, Martinique
- February (3): Northern Marianas, Argentina, Togo
- March (8): French Southern Territories, Algeria, Saba, South Korea, Kyrgyzstan, Georgia, Mauritius, Cocos Islands
- April (11): French Southern Territories, British Indian Ocean Territory, Latvia, Estonia, Kuwait, Saudi Arabia, Iraq, Iran, Turkmenistan, Kyrgyzstan, Ireland
- May (5): French Southern Territories, Iceland, Kyrgyzstan, China, Qatar
- June (7): Cocos Islands, Hong Kong, Slovenia, Spain, Portugal, Jersey, French Southern Territories
- July (6): Maldives, Ukraine, Honduras, French Southern Territories, US Virgin Islands, Malaysia
- August (9): Honduras, Cocos Islands, Lebanon, Albania, French Southern Territories, Israel, Iceland, Grenada, St. Vincent and the Grenadines
- September (4): Canada, Namibia, Chile, Central African Republic
One nation set an all-time monthly cold record in 2025: Qatar in January.
Hemispherical and continental temperature records in 2025
- Highest temperature ever recorded in South America in February: 46.5°C (115.7°F) at Rivadavia, Argentina, February 4
- Highest minimum temperature ever recorded in South America in February: 30.8°C (87.4°F) at Catamarca, Argentina, February 10.
Bob Henson contributed to this post.
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