ECWMF provide gridded seasonal forecast fields from 1981-2026:
cds.climate.copernicus.eu/datasets/sea...
but this doesn't include simple time series of Nino3.4 etc. so they'd have to be calculated from the fields and then anomalised etc.
This entry covers single-level data aggregated on a monthly time resolution.
Seasonal forecasts provide a long-range outlook of changes in the Earth system over periods of a few weeks or months, as a...
