Estuarine Forecasts at Daily Weather to Subseasonal Time Scales

Andrew C Ross,Gabriel A Vecchi,Vincent Saba,Marjorie A M Friedrichs,Ming Li,Kathleen Pegion,Raleigh R Hood,Keith W Dixon,Charles A Stock

doi:10.1029/2020ea001179

Abstract

AbstractMost present forecast systems for estuaries predict conditions for only a few days into the future. However, there are many reasons to expect that skillful estuarine forecasts are possible for longer time periods, including increasingly skillful extended atmospheric forecasts, the potential for lasting impacts of atmospheric forcing on estuarine conditions, and the predictability of tidal cycles. In this study, we test whether skillful estuarine forecasts are possible for up to 35 days into the future by combining an estuarine model of Chesapeake Bay with 35‐day atmospheric forecasts from an operational weather model. When compared with both a hindcast simulation from the same estuarine model and with observations, the estuarine forecasts for surface water temperature are skillful up to about 2 weeks into the future, and the forecasts for bottom temperature, surface and bottom salinity, and density stratification are skillful for all or the majority of the forecast period. Bottom oxygen forecasts are skillful when compared to the model hindcast, but not when compared with observations. We also find that skill for all variables in the estuary can be improved by taking the mean of multiple estuarine forecasts driven by an ensemble of atmospheric forecasts. Finally, we examine the forecasts in detail using two case studies of extreme events, and we discuss opportunities for improving the forecast skill.

Highlights

Ocean model forecasts of water levels, temperature, salinity, and other properties for estuaries and similar coastal regions have primarily focused on lead times of a few days into the future
We find that skill for all variables in the estuary can be improved by taking the mean of multiple estuarine forecasts driven by an ensemble of atmospheric forecasts
We tested whether skillful subseasonal forecasts for an estuary are possible by conducting forecast simulations using an estuarine model of Chesapeake Bay (ChesROMS) (Da et al, 2018; Xu et al, 2012) driven by forecasts from an atmospheric model from the Subseasonal Experiment (SubX) experiment (Pegion et al, 2019)

Summary

Introduction

Ocean model forecasts of water levels, temperature, salinity, and other properties for estuaries and similar coastal regions have primarily focused on lead times of a few days into the future. In the United States, a number of Operational Forecast Systems provide guidance for temperature, salinity, water levels, and currents for the 2 days for major coastal and estuarine regions including Chesapeake Bay (Lanerolle et al, 2011), the northern Gulf of Mexico (Wei et al, 2014), and San Francisco Bay (Peng et al, 2014). Experiments with both operational and research models have shown that short-term estuarine and coastal forecasts can help protect lives and property by predicting storm surges and inundation (Stanev et al, 2016) and by assisting with search and rescue operations (Cho et al, 2014) and can protect public and ecosystem health by forecasting the advection and dispersion of oil spills (Castanedo et al, 2006) and the development of ROSS ET AL. Much of the predictability at the seasonal time scale is driven by slow ocean modes, and skillful forecasts of monthly mean sea surface temperature (SST) have been produced for several large ocean regions (Hervieux et al, 2017; Hobday et al, 2016; Jacox et al, 2017; Siedlecki et al, 2016; Spillman & Alves, 2009; Stock et al, 2015)

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Discussion

Conclusion