Available here and including: MSLP charts, SST maps and NINO-index timeseries, 2m Temperature charts, 850mb Temperature charts, Geopotential height at 500Pa charts, Precipitation charts. The forecasts are updated every month and cover a time range of 6 months.
C3S Seasonal forecast archived data
Available through WebAPI, which is the method allowing users to download data in a programmatic way (using Python - example scripts are available).
Data from the Sectoral Information System (SIS)
EDgE: End-to-end Demonstrator for improved decision making in the water sector in Europe
SWICCA: Service for Water Indicators in Climate Change Adaption