The NCEP document titled 'ENSO: Recent Evolution, Current Status and Predictions' is updated every Monday.
Notes on verification
Multiple independent sources corroborate a weekly (Monday) update cadence for this specific NCEP/CPC PDF, and archived copies consistently show Monday dates. However, the document's own footnote references a monthly update for its headline probability statements, creating some internal ambiguity that keeps confidence from being 'high'.
Sources
- El Niño Today | El Nino Theme Page - A comprehensive Resource (pmel.noaa.gov)
- https://weather.gov/fwd/enso (weather.gov)
- https://wattsupwiththat.com/2011/09/08/a-note-regarding-the-noaa-enso-meter/ (wattsupwiththat.com)