The big idea: A tropical storm is a huge, spinning system of cloud and thunderstorms with very strong winds and torrential rain. The same hazard has three regional names: hurricane (Atlantic/east Pacific), typhoon (west Pacific/Asia) and cyclone (Indian Ocean/Australia).
Tropical storms are born over warm tropical oceans. The ocean is the engine: 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.
How this is tested: Paper 1 Option B opens with a data-response on a storm-track diagram or a world map of storm tracks. You State a compass direction of travel, State which region or continent a storm type hits, or Estimate the time a storm takes to travel between two marked points. Read the axis or scale carefully and quote the units.
| 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) |
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.
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. Examiners want the mechanism — warm water evaporates, the vapour rises and condenses, releasing latent heat that drives the storm upward and pulls in more air.
| 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 = 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 — higher peak winds, heavier rain, and a higher storm surge as warmer seas also raise sea level. Warmer water in new regions may also widen where storms can form. 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.