Tropical storms

Hurricanes, typhoons and cyclones are all the same kind of giant storm. They form over warm oceans and can bring destructive winds, rain and storm surges.

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Where and how they form

A tropical storm is a huge spinning low-pressure system.
Names: hurricane in the Atlantic and north-east Pacific, typhoon in the north-west Pacific, cyclone in the Indian Ocean and South Pacific.
They need warm ocean water: at least 26.5 degrees C (NOAA Hurricane Research Division). They form a little away from the Equator, usually between about 5 and 30 degrees north or south, because the Earth's spin is needed to make them rotate.
Warm, moist air rises fast, cools and condenses, releasing heat that powers the storm. Over land or cold water they lose their energy supply and weaken.

Structure and strength

At the centre is the eye: calm, with sinking air and clear skies.
Around it is the eye wall, with the strongest winds and heaviest rain.
Atlantic hurricanes are rated on the Saffir-Simpson scale from category 1 to 5, by wind speed. Category 5 has winds of at least 252 km/h (157 mph).

Effects and responses

Strong winds damage buildings. Heavy rain causes floods and landslides. A storm surge (sea pushed onto the land by wind and low pressure) floods coasts and is often the deadliest effect.
Hurricane Katrina (2005) flooded much of New Orleans in the USA when flood defences (levees) failed.
Typhoon Haiyan (2013) hit the Philippines; more than 6,000 people died, many from the storm surge.
Responses: satellite tracking and warnings, evacuation, storm shelters, stronger buildings and sea defences.
Worked example

Explain why tropical storms weaken when they move over land.

  1. Tropical storms get their energy from warm, moist air rising from the ocean.
  2. Over land, there is no warm sea to supply that moisture and heat.
  3. There is also more friction with the ground, so the winds slow down.

Answer: They lose their supply of warm, moist air from the ocean, and friction with the land slows the winds.

Key idea

Tropical storms (hurricanes, typhoons, cyclones) form over oceans of at least 26.5 degrees C, roughly 5 to 30 degrees from the Equator. Calm eye, violent eye wall. Saffir-Simpson scale 1 to 5. Effects: wind, rain, landslides and storm surges. Responses: tracking, warnings, evacuation, shelters.

Key words
Equator
The imaginary line around the middle of the Earth at 0 degrees latitude.
Scale
The link between distance on a map and on the ground. On a 1:50,000 map, 2 cm equals 1 km.

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Common mistakes
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Extra practice

2 more questions

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  1. What is a tropical storm called in the North Atlantic?

    1. A typhoon
    2. A hurricane
    3. A cyclone
    4. A tornado
    Show the answer

    Answer: A hurricane

    Hurricanes form in the Atlantic.

  2. Hurricanes only form over sea water that is at least about how warm, in degrees C?

    Show the answer

    Answer: 26.5 degrees C

    At least about 26.5 °C.

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Sources and references

Checked by the GCSE-ready editorial team, 23 October 2026. Last updated 2 October 2026. Spotted a mistake? Tell us and we will fix it.