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Air in motion · 5 min · 4 steps

How a typhoon forms

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Goal. Name the conditions a typhoon needs and explain where its energy comes from.

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Steps

  1. Predict

    Where could a typhoon grow?

    • Over warm sea, about 26.5 °C or more
    • Over cold sea
    • Over large deserts
    Show the answer

    Over warm sea, about 26.5 °C or more. Over warm sea: typhoons are powered by heat and moisture from water of about 26.5 °C or warmer.

    The line marks 26.5 °C. On its warm side the sea can power a typhoon. Warm water alone is not enough: the storm also needs moist air and light winds high above it.

  2. Warm, moist air rises. Its water vapour condenses into cloud and releases heat, which makes the air rise faster and draws in more moist air from below. Any active tropical storms are shown here with their forecast tracks.

  3. Typhoons rarely form within about 5° of the equator, because the Coriolis effect there is too weak to start the spin. In the northern hemisphere they turn anticlockwise.

  4. Typhoons near Taiwan are steered mostly by the winds around the edge of the large Pacific high-pressure area. Over land, or over cooler water, they lose their fuel and weaken; Taiwan's high mountains also break up their lower part.

The common mistake

Myth

Typhoons are fed by warm and cold air masses clashing, like winter storms.

Fact. A typhoon's fuel is the heat released when water vapour from the warm sea condenses into cloud. It has a warm core and no fronts. Mid-latitude winter storms are different: they feed on the contrast between warm and cold air.

Check yourself

Question 1

What is a typhoon's main source of energy?

  • Heat released as water vapour condenses
  • The clash of warm and cold fronts
  • The Sun heating the clouds directly
Show the answer

Heat released as water vapour condenses. Evaporation from the warm sea loads the air with water vapour; when it condenses in the storm's clouds the heat is released and drives the winds.

Question 2

Why do typhoons rarely form right on the equator?

  • The sea there is too cold
  • The Coriolis effect is too weak to start the spin
  • There is never any wind
Show the answer

The Coriolis effect is too weak to start the spin. The Coriolis effect is zero at the equator, so the inflowing air does not start to circle.

Question 3

Which way does a typhoon spin?

  • Clockwise
  • Anticlockwise
  • It changes from day to day
Show the answer

Anticlockwise. In the northern hemisphere tropical cyclones turn anticlockwise; in the southern hemisphere, clockwise.

Words in this lesson

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Curriculum

Taiwan 12-year curriculum (108 課綱), natural science
EMd-Vc-1 · EMd-Vc-2 · EMd-Vc-3 · Ib-Ⅳ-5
US Next Generation Science Standards
MS-ESS2-5 · MS-ESS3-2
England national curriculum
GCSE Geography: weather hazards (tropical storms)