Tropical and Extreme Weather Systems
What the exam tests
This domain tests tropical cyclone formation, structure, hazards and extreme weather systems.
Core rules
- Tropical cyclones require warm sea-surface temperature (about 26.5°C or more), high low-level humidity, Coriolis forcing and low vertical wind shear. They do not form within about 5° of the equator.
- Structure: a calm eye, a violent eyewall with the strongest winds, and spiral rainbands. In the Southern Hemisphere circulation is clockwise around the low.
- Hazards include extreme wind, torrential rain, flash flooding, storm surge, tornadoes and severe turbulence.
- Stages progress from tropical disturbance to depression, tropical storm and cyclone; forecast tracks have uncertainty, so use a safety margin.
Worked example
A system at 15°S over 28°C water has a falling central pressure and 40 kt winds. The reasoning is that warm water and low shear favour intensification, while its latitude allows Coriolis organisation. Expect the wind field and sea state to worsen; do not plan a track through the forecast cone.
Traps
Expecting cyclones at the equator; using Northern Hemisphere rotation; treating the eye as harmless; ignoring storm surge and flooding.