Inputs to the Model

Open Ocean Boundary

The open ocean boundary in the model is forced with water levels, salinity and temperature. Water levels for the nowcast are derived from observations at a nearby CO-OPS tide gauge in Mayport. For the forecast, the water level is determined by adding the tide prediction at Mayport with forecasts of the subtidal water level made by the National Weather Service's Extratropical Storm Surge model. The open ocean boundary salinity is specified as 35 PSU (practical salinity units) at the surface and linearly increases to 36 PSU at the bottom. These values are held constant in time. Temperatures are forced with values based on climatology.

River Discharge

The upstream limit of the grid is at Buffalo Bluff, just north of Lake George. Real-time river discharge, temperature and conductivity are available from the USGS at Buffalo Bluff. These are used as the upstream boundary condition to represent the main-stem flow of the St. Johns River. Even at this upstream boundary, Buffalo Bluff is affected by the ocean tide. Therefore, the net discharge can potentially be negative (directed upstream) at times. To help prevent artificial reflection of the tides at Buffalo Bluff, a sponge boundary condition is used. Real-time river discharge is also specified at Dunns Creek, Rice Creek, Etonia Creek, Simms Creek, Deep Creek, South Fork Black Creek, North Fork Black Creek, and Black Creek near Doctors Inlet. For the forecast, river discharge is currently persisted from the last value in the nowcast.

Atmosphere

For the nowcast, winds are currently derived from the CO-OPS station in Mayport. The forecast uses winds computed interpolated from the ETA-12 model at the same Mayport location.