The nature of tropical storms and their underlying causes. Forms of storm…

The idea

Tropical storms are intense low-pressure systems. Their underlying causes require sea surface temperatures above 27 °C, ocean depth of 70 m, and sufficient Coriolis force (5° to 20° from the equator), dictating their spatial distribution. They generate multiple hazard forms: high winds destroy infrastructure, while low pressure creates devastating storm surges and coastal flooding. Intense rainfall triggers river flooding and destabilises slopes, causing landslides. Magnitude is measured using the Saffir-Simpson scale. While their frequency and regularity vary seasonally, satellite tracking improves predictability, though exact land-fall paths remain uncertain.

What earns the marks

• Explain the atmospheric conditions required for tropical storm formation, including sea surface temperatures of at least 27 °C and the Coriolis effect.
• Identify the primary forms of storm hazard, distinguishing between direct impacts like high winds and secondary hazards like landslides and river flooding.
• Describe the spatial distribution of tropical storms, noting their concentration in specific oceanic basins between 5° and 20° latitude.
• Evaluate the predictability of tropical storms, discussing how satellite monitoring tracks paths but cannot perfectly forecast intensity or exact landfall.
• Assess how magnitude is categorised using the Saffir-Simpson scale based on sustained wind speeds and central pressure.

Common mistakes and how to put them right

• Confusing storm surges with tsunamis.

  Put it right by explaining that storm surges are driven by low atmospheric pressure and wind, not seismic activity.

• Stating that tropical storms form on the equator.

  Put it right by noting they form between 5° and 20° latitude because the Coriolis force at the equator is zero.

• Treating frequency and regularity as identical concepts.

  Put it right by defining frequency as the number of events per year, and regularity as the temporal spacing or seasonal pattern of these events.

Exam tips

• Use specific data when discussing magnitude, such as referencing Category 5 storms having sustained winds over 252 km h⁻¹.
• Link the physical causes of the storm directly to the resulting hazards, such as explaining how intense low pressure physically lifts the sea level to create a storm surge.
• When evaluating predictability, acknowledge the difference between predicting the seasonal occurrence (high predictability) and the exact track or intensity at landfall (lower predictability).