Ocean state estimation, often referred to as Ocean Reanalysis (ORA), is now routinely used for ocean initialization of seasonal forecast models and to monitor the thermal structure in the tropical Pacific. Advanced real-time ocean monitoring tools for ENSO (El Nino/Southern Oscillation) are now also being put in place. These diagnostics could potentially improve operational ENSO monitoring and forecasts by further enhancing our understanding of the physical processes in the evolution of ENSO events. Beyond ENSO, other climate modes of variability that are of societal interest include the Indian Ocean Dipole, Tropical Atlantic Variability, and the Pacific Decadal Oscillation (PDO). Preliminary monitoring tools have also been developed for these modes. The availability of multiple ORAs provides an opportunity to assess uncertainties in the products, to help identify gaps in observing systems as they impact forecasts, identify deficiencies in data assimilation schemes. They also provide the basis for future development of multi-model ensemble monitoring products.