La Niña is officially declared when central-eastern Pacific water temperatures stay at least 0.5°C below average.
Notes on verification
Confirmed by NOAA, National Weather Service, and academic sources. The 0.5°C threshold is accurate, though full La Niña declaration also requires the anomaly to persist for multiple seasons and be accompanied by atmospheric changes, which is a minor nuance not captured in the claim.
Sources
- Say Goodbye to a Historic El Niño and Hello to La Niña (smithsonianmag.com)
- https://www.climate.gov/news-features/blogs/enso/november-2024-enso-update-ask-me-anything (climate.gov)
- https://www.weather.gov/arx/why_lanina (weather.gov)
- https://www.climate.gov/news-features/blogs/enso/april-2025-enso-update-la-nina-has-ended (climate.gov)
- https://courses.ems.psu.edu/meteo3/node/2272 (courses.ems.psu.edu)