Physical geography · GCSE Geography
Tropical storm formation
GCSE Geography tropical storm formation: warm oceans, the Coriolis effect, low wind shear, and why storms weaken over land — the process diagram examiners want labelled.
Warm sea, moisture, spin, low shear — then a named storm like Haiyan to land the process on a place.
The important bits
What you need to know
- 1
Tropical storms (hurricanes, typhoons, cyclones — same phenomenon, different ocean basins) are intense low-pressure systems with strong winds and heavy rain.
- 2
Sea surface temperature must be about 27°C or higher to provide energy through evaporation and latent heat release when water vapour condenses in towering cumulonimbus clouds.
- 3
Formation occurs roughly between 5° and 20° latitude: enough Coriolis force to spin the system, not so near the equator that spin is too weak.
- 4
Moisture from warm oceans fuels convection. Air rises, cools, condenses, releases heat, lowers pressure, draws in more warm moist air — a positive feedback.
- 5
Low wind shear (little change in wind speed/direction with height) lets the storm organise vertically. High shear tears the top off and weakens development.
- 6
Stages: tropical disturbance → depression (closed circulation) → storm (named when wind thresholds met) → hurricane/typhoon/cyclone category by sustained wind speed (Saffir–Simpson for Atlantic).
- 7
Over land, the fuel supply (warm water) is cut off; friction and dry air weaken the system. Storm surge can still devastate coasts on landfall.
- 8
Distribution: Atlantic/Caribbean/Gulf (hurricane), NW Pacific (typhoon — Haiyan), Indian Ocean/South Pacific (cyclone). Not random: tracks follow ocean warmth and season.
Quotations worth analysing
Short evidence. Real method.
“Typhoon Haiyan (Yolanda) crossed the Philippines in November 2013 as one of the strongest landfalling storms recorded.”
Use Haiyan for formation + impact: warm Pacific, low latitude, then storm surge at Tacloban. Process and place in one answer.
“Hurricane in the Atlantic, typhoon in the NW Pacific, cyclone in the Indian Ocean.”
Same storm type, different names. Examiners punish “typhoon in the Caribbean”.
Go deeper
The formation diagram in words
Draw or narrate: warm ocean (>27°C) → evaporation and rising moist air → condensation releases latent heat → air rises faster, pressure drops at surface → winds spiral inward (Coriolis gives spin in hemisphere) → eye forms with calm centre and violent eyewall → if wind shear stays low, storm intensifies. Labels beat adjectives. “Huge and scary” is not a process mark. “Latent heat release lowers central pressure” is.
Go deeper
Why Haiyan’s surge was the killer
Wind damage was severe; in Tacloban the killer was storm surge funnelled into a shallow bay. Formation geography (warm Pacific, low shear) explains the storm’s power; coastal geography (bay shape, low-lying city, poverty) explains the death toll. Management: warnings issued, but logistics and shelter quality failed. Mangrove loss increased exposure. Link formation to impact in 9-markers: same storm, different vulnerability ashore.
See the idea in action
Question: explain how a tropical storm forms. Warm sea (>27°C) evaporates moisture. Air rises, condenses, releases latent heat, lowering pressure. Coriolis spin organises winds between 5° and 20°. Low wind shear keeps the column upright. Named example: Haiyan 2013 over warm NW Pacific. Over land, fuel cuts off and winds decay — but surge can still flood coasts.
Exam technique
Turn knowledge into marks
Learn one annotated formation sequence and one named storm. Every hazards paragraph needs a place and a number if you have one.
Common mistakes
Do not give these marks away
- 01
Saying storms form on the equator (Coriolis too weak).
- 02
Confusing hurricane, typhoon and cyclone basins.
- 03
Explaining formation with no reference to warm ocean or latent heat.
Which condition is essential for tropical storm formation?
ASea surface temperature around 27°C or higher
BFrozen polar seas
CStrong vertical wind shear throughout the troposphere
DFormation directly on the equator at 0° latitude
Show the answer
Sea surface temperature around 27°C or higher. Warm oceans provide energy through evaporation and latent heat. Equatorial formation lacks spin; high shear disrupts organisation.
Quick questions
If this is the bit you searched
What is the difference between a hurricane and a typhoon?
Regional names for the same type of tropical storm: hurricane in the Atlantic and NE Pacific, typhoon in the NW Pacific, cyclone in the Indian Ocean and South Pacific.
Why do tropical storms weaken over land?
They lose the warm water energy source, face increased friction, and ingest dry continental air.