The Open Ocean Giant
The standard wave model used globally is called WAVEWATCH III. It is developed by NOAA. It is incredible at predicting swell across the Pacific Ocean.
- The Flaw: It assumes deep water. It does not understand shallow reefs, sandbars, or friction from the sea floor.
The Nearshore Specialist
When waves approach the coast, physics changes. The bottom of the wave drags on the sand. The wave slows down and bends. This is called "refraction."
- The Solution: Scientists use a different model called SWAN (Simulating WAves Nearshore). It was built by Delft University in the Netherlands.
- How it works: SWAN takes the data from WAVEWATCH III and recalculates it for shallow water. It accounts for depth, current, and breaking.
The "A-Ha" Moment
If you check a forecast for a specific beach, make sure it uses a SWAN model (often 1.3km resolution). If it uses the raw global model, it will predict 10-foot waves even if the bay is blocked by an island.
Model Comparison
WAVEWATCH III
Global ocean model
Deep water physics
Best for: Open ocean swell
SWAN
Nearshore model
Shallow water physics
Best for: Beach forecasts
The Nesting Process
Modern forecasts use both models together. WAVEWATCH III predicts the energy in the open ocean. SWAN takes that energy and calculates how it transforms as it approaches your beach.
Summary
Global models predict energy. Local models (SWAN) predict the actual wave at your beach.
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