Storm Surge Calculator
Simplified educational estimate only — not a real storm-surge forecast (real forecasts use SLOSH/complex hydrodynamic models).
Two Forces That Push Water Onto the Coast
Storm surge is the abnormal rise in seawater level a tropical or coastal storm pushes ashore, and it comes from two combining effects: the inverse barometer effect, where extremely low central pressure literally allows the sea surface to bulge upward beneath the storm, and wind setup, where sustained onshore winds physically pile water against the coastline. This calculator applies simplified versions of both effects to illustrate how they scale with storm intensity.
The Formulas
Wind setup(cm) = (Wind Speed(mph) ÷ 10)² × 5
Total surge = Inverse barometer surge + Wind setup
The inverse barometer approximation of roughly 1 cm of sea-level rise per millibar of pressure drop below ambient is a commonly cited rule of thumb. The wind setup term here is a simplified educational approximation showing how surge grows sharply, not linearly, with wind speed — real wind setup also depends heavily on coastal shape, water depth, and fetch, none of which this simplified model captures.
Worked Examples
| Central pressure | Sustained wind | Inverse barometer | Wind setup | Total estimated surge |
|---|---|---|---|---|
| 980 mb | 70 mph | 33.0 cm | 245.0 cm | 278.0 cm (≈9.12 ft) |
| 950 mb | 100 mph | 63.0 cm | 500.0 cm | 563.0 cm (≈18.47 ft) |
In this simplified model, wind setup dominates the total far more than the pressure-driven term, which mirrors real storm surge behavior — wind-driven water piling is generally the larger contributor along most coastlines.
Where This Matters
- Understanding evacuation zone rationale — coastal evacuation orders are driven primarily by storm surge risk, not wind speed alone, which is why a "weaker" storm on the wind scale can still produce catastrophic surge.
- Illustrating storm intensity relationships — comparing how surge estimates change with central pressure and wind speed helps explain why storm categorization by wind speed alone doesn't fully capture flood risk.
- Educational and planning discussions — this simplified model is useful for understanding the physics at a conceptual level; actual surge forecasts for real decision-making should always come from official sources like the National Hurricane Center.
How to Use This Calculator
- Enter the Storm Central Pressure in millibars.
- Enter the Sustained Wind Speed in mph.
- Enter the Ambient Pressure in millibars (optional — defaults to 1013).
- Select Calculate to see the estimated surge in feet and centimeters.
Related Calculations
Check how atmospheric pressure varies with elevation using the Barometric Pressure Calculator, or see accumulated rainfall totals with the Rainfall Accumulation Calculator.