Development of Long Range Hypoxia Forecasts for the Northern Gulf of Mexico

Gulf hypoxia has received considerable scientific and policy attention because of its large size (up to 23,000 square km), potential ecological and economic effects, and the need to understand the implications of various nutrient management strategies in the Mississippi River watershed. Over the past 20 years, a number of different models have been developed to simulate the severity and areal extent of hypoxia in the northern Gulf of Mexico, and to predict the consequences of management actions. The models range from simple statistical models to complex three-dimensional fully coupled hydrodynamic-biogeochemical models. The size and the complexity of these models have been steadily increasing due to developments in computer technology and computational techniques, and also in response to new scientific paradigms that have emerged over time forcing modelers to broaden the scope of their original models. We report on a novel long range hypoxia forecasting system that was implemented and tested in conjunction with the 2019 Gulf hypoxia monitoring cruise. The modeling system is based on a high-resolution, three-dimensional, coupled hydrodynamic-biogeochemical model that is driven by a number of observational and forecasting products, including weather forecasts, tidal and subtidal forcing at the open Gulf of Mexico boundary, riverine freshwater and nutrient loads, heat flux, short wave radiation, and surface wind stress. The model was run in the hindcasting mode from January 1 until July 17, 2019, and in the forecasting mode from July 18 until July 31, 2019. The preliminary results are encouraging and the 10-day model forecast issued on July 21, 2019, closely approximated the areal extent of hypoxia observed during the July 23 – July 30 monitoring cruise with an overall error of about 10%.