Released in the Spring of 2026, Version 3 of GEOS-S2S enhances spatial resolution and ensemble size, with 40 ensemble members for the first three months, to provide more skillful sub-seasonal forecasts. Meteorological and aerosol information from the GMAO’s GEOS-IT product is incorporated into a one-way, weakly coupled analysis (GI-Ocean), which is used to initialize the seamless S2S system. The system emphasizes the use of NASA’s altimetry and sea-surface salinity observations and retains the representation of indirect aerosol forcing on the seasonal projections.

Version 2 of GEOS-S2S was the GMAO’s production system between late 2018 and Spring 2026, when it was discontinued. The atmospheric and weakly coupled ocean assimilation used information from GMAO’s FPIT meteorological fields. This system provided contributions to NOAA’s National Multi-Model Ensemble (NMME) project, NOAA’s subseasonal forecasting experiment (SubX), and other international projects. GEOS-S2S-2 was unique in that it included aerosols as part of the prediction and, through use of a two-moment cloud microphysics scheme, it captured the indirect aerosol forcing effects.

Version 1 was GMAO’s production system from 2012 until late 2018, when it was discontinued. This system was GMAO’s first to contribute to NOAA’s National Multi-Model Ensemble (NMME) project and to NOAA’s Real Time Multiple Ocean Reanalysis Intercomparison.