This proposed National Oceanographic Partnership Program project is a collaborative effort between RSMAS and NOAA/AOML to perform Observing System Simulation Experiments (OSSEs) to determine optimum observing strategies for monitoring the Atlantic Meridional Overturning Circulation (AMOC). The most accurate possible three-dimensional estimates of the ocean state are realized by optimally combining observations with ocean model dynamics. Optimal estimates of the state of the AMOC and early detection of significant changes should therefore be obtained by constraining a data-assimilative ocean general circulation model with measurements from a cost-effective observing system. To design an efficient system, it is necessary to first identify the critical variables to be measured, the spatial configuration of sensors, and the frequency of measurements necessary to identify and to characterize temporal and spatial fluctuations. OSSE’s provide an objective means to quantitatively evaluate different observing system strategies. The PIs therefore propose to use the U. S. Navy ocean nowcast-forecast system based on the Hybrid-Coordinate Ocean Model (HYCOM) to perform OSSEs to evaluate potential AMOC observing systems.