Beaufort scale and hurricane categories
An online tool for the wind-force scales: the full Beaufort table from calm to hurricane with what the wind actually does at each force, the Saffir-Simpson hurricane categories, and a computed wind field for a tropical cyclone — set a speed, drop the eye on the map, and see what wind reaches each city. The field comes from the published Willoughby model rather than from circles drawn around a point.
How to use it
Drag the maximum wind, the forward speed and the heading — or pick one of the real storms with its actual parameters.
Click the map. The category contours redraw at once, and which side of the storm is stronger becomes visible.
Search for it or press "Locate me" — the card reports the wind speed, the Beaufort force, and what that wind does.
The tables below turn any speed into a force and a category, and explain how the two scales differ.
See what each wind force does, and how far a hurricane reaches
1The storm
2How far the wind reaches
The coloured contours are category boundaries by wind speed. They are lopsided, and that is not an error: a hurricane carries its own motion with it, so on the side where the rotation runs with the track — the right-hand side in the northern hemisphere — the wind is faster, and the gap between the two flanks is the forward speed of the storm itself. The white dashed circle is the radius of maximum wind, which is the eyewall. The streamlines show which way the wind blows, not only how hard.
3The wind where you are
—
Settlements of 15,000 people and above (GeoNames). These are open-terrain wind speeds at 10 m: a real gust among buildings or along a coast will differ, and terrain can multiply it.
4A cut through the hurricane
The wind does not fall away from the centre — it climbs from near calm in the eye to the wall, and only then decays. The decay runs on two exponentials, a fast one near the wall and a slow one outside, which is why a large typhoon spreads gale-force wind hundreds of kilometres beyond anything visible on a cloud image.
5The Beaufort scale, force by force
| Force | Name | Speed, km/h | What happens |
|---|---|---|---|
| 0 | Calm | 0–1 | Smoke rises vertically; the water is a mirror. |
| 1 | Light air | 1–6 | Smoke drifts, but a weather vane does not turn; ripples without crests. |
| 2 | Light breeze | 6–12 | Wind felt on the face, leaves rustle, the vane begins to move. |
| 3 | Gentle breeze | 12–20 | Leaves and small twigs in constant motion; light flags extend. |
| 4 | Moderate breeze | 20–29 | Raises dust and loose paper; small branches move. |
| 5 | Fresh breeze | 29–39 | Small trees sway; crested wavelets form on inland water. |
| 6 | Strong breeze | 39–50 | Large branches move, wires whistle, umbrellas become hard to hold. |
| 7 | Near gale | 50–62 | Whole trees in motion; walking into the wind takes real effort. |
| 8 | Gale | 62–75 | Twigs break off trees; walking into the wind is barely possible. |
| 9 | Strong gale | 75–88 | Slight structural damage: chimney pots and slates are removed. |
| 10 | Storm | 88–103 | Trees uprooted, considerable structural damage. Rarely experienced inland. |
| 11 | Violent storm | 103–118 | Widespread damage. Very rarely experienced on land. |
| 12 | Hurricane force | > 118 | Devastating damage. The Beaufort scale stops here; the hurricane scale begins. |
The Beaufort scale describes wind by WHAT IT DOES — it was invented so a sailor with no instruments could name the wind from the look of the sea. The bounds are for the 10-minute mean at 10 m; gusts run about half as much again. Force 12 is the top of the scale: it simply stops there, and the hurricane scale begins.
6The Saffir-Simpson scale: hurricane categories
| Cat. | Name | Speed, km/h | What happens |
|---|---|---|---|
| — | Tropical storm | 63–117 | Not yet a hurricane. Breaks branches, lifts anything loose; dangerous for its rain and surge. |
| 1 | Category 1 | 119–152 | Damage to roof, shingles, gutters. Branches snap, shallow-rooted trees topple, power lines come down. |
| 2 | Category 2 | 154–176 | Major roof and siding damage. Many trees uprooted, power lost for days to weeks. |
| 3 | Category 3 | 178–207 | Devastating damage: roof decking and gable ends removed. Water and electricity may be out for weeks. |
| 4 | Category 4 | 209–252 | Catastrophic damage: loss of most of the roof and some exterior walls; the area may be uninhabitable for months. |
| 5 | Category 5 | > 254 | Catastrophic damage: a high percentage of homes destroyed; the area is uninhabitable for a long time. |
The categories are defined in knots: 64, 83, 96, 113 and 137. The familiar km/h figures are rounded conversions of those, so a table rebuilt from round kilometres shifts the boundaries and files a borderline storm under the wrong category. This one counts from knots. And the important part: a category is about WIND ONLY. Most deaths come from water — storm surge and rain — and that depends on the shape of the coast and the depth beside it, not on the category.
Models: wind field — Willoughby, Darling & Rahn (2006), with coefficients from the `stormwindmodel` reference implementation; wind-pressure relation — Atkinson & Holliday (1977); gradient-to-surface reduction — 0.9 over water, 0.72 over land. Cities — GeoNames (CC BY 4.0). Storm surge is not modelled.
