The Extratropical Surge and Tide Operational Forecast System (ESTOFS) Atlantic implementation and skill assessment
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The Extratropical Surge and Tide Operational Forecast System (ESTOFS) Atlantic implementation and skill assessment
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    "The Coast Survey Development Laboratory (CSDL) of the National Ocean Service (NOS) and the Environmental Modeling Center (EMC) of the National Centers for Environmental Prediction (NCEP) have collaborated to establish an Extratropical Surge and Tide Operational Forecast System (ESTOFS) for the Western North Atlantic basin. The hydrodynamic model employed for ESTOFS is the ADvanced CIRCulation (ADCIRC) finite element model (Luettich et al. 1992; Luettich and Westerink 2004). The ADCIRC hydrodynamic model has several beneficial features for this system and has been demonstrated to be effective at predicting tidal circulation and storm surge propagation in complex coastal systems. Its unstructured grid methodology allow for the propagation of storm surges from offshore, across the shelf, and inland. This grid can also readily and accurately represent irregular shorelines including barrier islands, rivers and waterways. The ESTOFS was implemented operationally by NCEP Central Operations (NCO) to provide forecasts of surge with tides, astronomical tides, and sub-tidal water levels (the isolated surge) throughout the domain. The ESTOFS provides the National Weather Service (NWS) with a second extratropical surge system in addition to the Extratropical Storm Surge (ETSS) that currently is based on the Sea Lake and Overland Surge from Hurricanes (SLOSH) model (Jelesnianski et al. 1992). The ESTOFS differs from ETSS by combining the surge with tides and utilizes unstructured grids which can provide better resolution at the coast. This capability serves the needs of NCEP's Ocean Prediction Center (OPC) and the National Hurricane Center's Tropical Analysis and Forecast Branch (NHC/TAFB), which are responsible for providing offshore marine forecasts. It also meets the needs of Weather Forecast Offices for putting out coastal inundation forecasts. The ESTOFS is also designed to provide the surge with tides to WAVEWATCHIII® (WW3) for coupling waves with coastal water levels. Therefore, ESTOFS set-up is patterned after WW3: it uses the same Global Forecast System (GFS) forcing and has the same forecast cycle and length, and runs concurrently at NCO. As part of the establishment of ESTOFS, CSDL has evaluated application of the ADCIRC hydrodynamic model on the Western North Atlantic which is implemented to perform operational 180-hour forecasts. The model results are compared with observations at 69 stations using NOS's standard skill assessment software. The skill assessment focuses on the performance of the model in simulating water levels in three model run scenarios: 1) astronomical tide, 2) model hindcast, and 3) semi-operational forecast. The skill statistic criteria for water levels either pass or are close to the NOS criteria for the astronomical tide scenario. For the hindcast simulation scenario, which is a one year simulation, the skill scores for combined water levels are satisfied with the NOS criteria except for some stations which are located in complex geometries where the model grid doesn't have enough resolution. The semi-operational forecast scenario, which is a 2 week simulation, does not meet the NOS criteria. This might be attributed to a couple of different reasons. The first could be a river discharge inflow, and the second could be seasonal variation in water levels due to baroclinic effects. The ESTOFS does not incorporate them. Even though the ESTOFS includes these uncertainties, the model's water level forecasts are of good accuracy"--Executive Summary.
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