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Reading the weather · 4 min · 4 steps

How strong is that wind?

In the appThis lesson needs data the website does not show yet.

Goal. Read wind speed and the Beaufort scale, and explain why wind is strongest over open sea.

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Steps

  1. Predict

    A gale is force 8 on the Beaufort scale. How fast is that?

    • About 20 km/h
    • About 62 to 74 km/h
    • About 200 km/h
    Show the answer

    About 62 to 74 km/h. Force 8, a gale, is 62 to 74 km/h: strong enough to break twigs off trees.

    Taipei's card shows the wind speed and its Beaufort force, from 0 (calm) to 12 (hurricane force). Tap any other city to compare.

  2. Admiral Francis Beaufort drew up his scale in 1805 for sailors, by what the wind did to a warship's sails. It was later rewritten for what you see on land: force 3 moves leaves and small twigs, force 6 moves large branches and makes umbrellas hard to use.

  3. The speed on the card is a forecast of the average wind, 10 metres above the ground. Gusts, short bursts of stronger wind, can be much faster, especially among tall buildings and in the mountains.

  4. The streak colours show the speed everywhere. Some of the windiest seas on Earth surround Antarctica, where the westerlies blow with no land to slow them: sailors call these latitudes the Roaring Forties and the Furious Fifties.

The common mistake

Myth

The wind is the same strength at street level as higher up.

Fact. Friction with the ground slows the wind, so it is usually stronger higher up and over open sea than in a city street. Weather reports use the speed 10 metres above open ground so that places can be compared.

Check yourself

Question 1

What does Beaufort force 0 mean?

  • Calm
  • Hurricane force
  • A gale
Show the answer

Calm. Force 0 is calm, under 1 km/h: smoke rises straight up.

Question 2

Why are the Roaring Forties so windy?

  • No land slows the westerlies there
  • Volcanoes heat the air
  • The Moon pulls the air
Show the answer

No land slows the westerlies there. Around Antarctica the westerlies circle the globe over open ocean with almost no land to slow them.

Question 3

What is a gust?

  • A short burst of stronger wind
  • The average wind speed
  • A change in wind direction only
Show the answer

A short burst of stronger wind. Gusts last a few seconds and can be much stronger than the average speed.

Words in this lesson

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Curriculum

Taiwan 12-year curriculum (108 課綱), natural science
Ib-Ⅳ-2
US Next Generation Science Standards
MS-ESS2-5
England national curriculum
KS3 Geography: weather and climate