The big idea: A tropical storm is a huge, spinning system of cloud and thunderstorms with very strong winds and torrential rain.
| Name | Where |
|---|---|
| Hurricane | Atlantic / east Pacific |
| Typhoon | West Pacific / Asia |
| Cyclone | Indian Ocean / Australia |
The ocean is the engine: Tropical storms are born over warm tropical oceans. Warm surface water gives off heat and moisture that powers the storm. This is why Option B treats them as an ocean-atmosphere interaction — the sea drives the weather above it.
Key terms
- Tropical storm — a large, rotating low-pressure system with strong winds and heavy rain, fuelled by a warm ocean.
- Sea-surface temperature (SST) — the temperature of the top of the ocean; storms need about 26.5 °C or warmer.
- Evaporation — warm water turning to water vapour, lifting heat and moisture into the air.
- Latent heat — the energy released when that vapour condenses into cloud; this is the storm's fuel.
- Coriolis effect — the spin of the Earth that makes the storm rotate (and stops storms forming right on the Equator).
- Storm surge — the wall of seawater the winds push ashore — the deadliest part of the hazard.
Warm sea = the fuel: If the sea surface is warm (≥ 26.5 °C and deep enough), a storm has plenty of fuel and can intensify.
When the storm moves over cool water or land, the fuel is cut off and it weakens. Track + sea temperature together explain why a storm grows then dies.
Where tropical storms occur and what they do to coasts
- Distribution — between about 5° and 20° from the equator over warm oceans: hurricanes in the Atlantic and eastern Pacific, typhoons in the western Pacific, cyclones in the Indian Ocean and around Australia. They move westwards, then curve polewards.
- Storm surge — low pressure and onshore winds raise the sea, flooding low coasts; surges cause most hurricane deaths.
- Physical impacts — beach and dune erosion, cliff retreat, broken reefs and uprooted mangroves, salt in soils and wells.
- Case study: Typhoon Haiyan (Philippines, 2013) — one of the strongest storms recorded at landfall; a surge of over 5 metres swept through Tacloban, and more than 6,000 people died.
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How this is tested: The figure here is a storm-track diagram (a predicted path with values along it) or a world map of cyclone tracks.
The data-response marks come from short reads
- State a compass direction of travel, or the continent a storm type hits.
- Estimate the time between two marked points.
- Estimate a value off the track (wind speed / sea-surface temperature).
Read it carefully: Always read the axis or scale carefully and quote the units.
Read the x-axis (hours) first. Estimate the hour of peak wind, and read off how the storm weakens once the sea cools.
Interactive diagram
Explore the labelled diagram, charts and maps for this topic in full study mode.
Predicted track of a tropical storm (read this for the data question)
| Hour | Sea-surface temp (°C) | Wind speed (km/h) | Direction of movement |
|---|---|---|---|
| 0 | 29 | 120 | WNW |
| 18 | 30 | 175 | WNW |
| 36 | 30 | 220 | W |
| 54 | 27 | 165 | WNW |
| 72 | 24 | 95 | NW |
| 90 | 21 | 55 | N (over land) |
Using the intensity graph: (a) state the hour at which the storm reaches its strongest winds; (b) estimate the wind speed at hour 72.
Model answer plan
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Estimate elapsed time = subtract the two times: To estimate how long a storm takes between two points, read the time at each point off the track and subtract. On a real map you measure the distance with the scale and divide by the storm's speed — but with a timed track you just take the gap in hours.
Using the predicted-track table above: (a) state the direction the storm is moving at hour 0; (b) state the sea-surface temperature at hour 36; (c) estimate how many hours pass between hour 0 and the moment the storm reaches its strongest winds.
Model answer plan
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Quote units, name the direction in full: Give SST in °C, speed in km/h, time in hours, and write a compass direction in full (WNW, not just 'left'). Markers accept close compass values (e.g. W or NW for WNW).
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Tropical storms only form where several conditions come together over a warm ocean. The warm sea supplies the energy; the other conditions let that energy build into a rotating storm.
The mechanism examiners want
Evaporation
Warm water evaporates.
Rising and condensing
The vapour rises and condenses.
Latent heat
Condensation releases latent heat.
The storm grows
That heat drives the storm upward and pulls in more air.
Evaporate, condense, release latent heat, pull in more air.
Conditions needed for a tropical storm to form
| Condition | Why it is needed |
|---|---|
| Warm ocean (≥ 26.5 °C) | Supplies heat + moisture by evaporation — the storm's energy source |
| Ocean warm to ~50 m depth | Keeps the fuel supply going as the storm churns the surface |
| 5–20° latitude (off the Equator) | Enough Coriolis effect to make the system spin |
| Low wind shear | Lets the tall storm clouds stay stacked instead of being torn apart |
| Unstable, humid air / low pressure | Lets warm moist air keep rising and condensing |
The warm-ocean mechanism (learn this chain)
- Warm sea (≥ 26.5 °C) → fast evaporation lifts heat and water vapour into the air.
- The moist air rises and cools, the vapour condenses into cloud and releases latent heat.
- That heat warms the air further, so it rises faster, pressure falls, and more air is drawn in — the storm intensifies.
- The Coriolis effect makes the whole system rotate into a spinning storm.
Outline why tropical storms tend to form over warm tropical oceans.
Model answer plan
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Outline = reason + development: An Outline [2] needs one reason and one development, not a list of four reasons. Warm ocean (reason) → more evaporation supplies the energy/latent heat that powers the storm (development).
Warm water made Hurricane Irma a monster: Hurricane Irma (2017) crossed unusually warm Atlantic water near 30 °C and reached Category 5 with winds around 285 km/h, battering the Caribbean and Florida. When it finally tracked over cooler water and land, the fuel was cut off and it weakened — exactly what the SST column in a track table shows.
Why warming oceans matter: Because warm water is the fuel, warmer oceans can make tropical storms more intense.
What warmer oceans can do
- Higher peak winds.
- Heavier rain.
- A higher storm surge, as warmer seas also raise sea level.
- A wider area where storms can form, as warmer water reaches new regions.
The bridge to the essay: This is the bridge from Option B science to a real-world vulnerability and resilience argument.
How a warmer ocean can raise the danger
- More energy — hotter water evaporates faster, so storms can reach higher wind speeds.
- Wetter storms — warmer air holds more vapour, giving heavier rain and worse flooding.
- Higher surge — a warmer ocean is a higher ocean, so the storm surge floods further inland.
- Hit on coral and coasts — storms plus warming bleach reefs (the Great Barrier Reef) and erode soft coasts (the Dawlish line in England), removing natural defences.
How this is tested — the [10] Examine essay: Paper 1 Option B ends with a 10-mark Examine essay, marked on markbands. A recurring version asks whether warming oceans are making tropical storms more dangerous.
Top band needs: accurate terms (SST, latent heat, storm surge), two or more developed points with named examples, a weighing of how much is ocean warming versus vulnerability, and a clear judgement.
Examine the view that warming oceans are making tropical storms more dangerous.
Model answer plan
See the answer broken into clear points, with guidance on how each point earns marks.