Predict the Break
Every surfer knows the set comes in threes. But when? This engine calculates the exact window when your swell matures—when peak period hits the shelf and the face opens up. Not vibes. Physics.
Typical Gulf breeze: 8–15 m/s
Distance wind blows uninterrupted
How long the wind holds steady
Depth at the breaking zone
Peak Period
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Significant Height
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Group Velocity
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Set Arrival Window
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Break Quality
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The Math Behind the Wall:
This calculator implements the
Where
Group velocity derives from the deep-water dispersion relation:
See the companion data file for full coefficient tables and uncertainty bounds.
This calculator implements the
Hasselmann (1960) fetch-limited growth relations:T_p = 0.83 × (g×U/c_w)^{0.33} × F^{0.33}H_s = 0.0025 × (g×F/c_w^2) × tanh[0.00515 × (U^2/gF)]Where
T_p is peak period, H_s is significant wave height, F is fetch length, U is wind speed, c_w is wind-wave coupling constant, and g is gravity (9.81 m/s²).Group velocity derives from the deep-water dispersion relation:
v_g = ½ × √(g/k), where k is the wavenumber.See the companion data file for full coefficient tables and uncertainty bounds.
Grounded in: Hasselmann, K. (1960). On the spectrum of wind-generated ocean waves. Zeitschrift für Geophysik, 26, 271–286. | NOAA Coastal Services Center Wave Atlas (2023). | Data schema: set-window.json