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Unlock This CourseTropical cyclones are amongst the most powerful and destructive weather systems on Earth. These massive rotating storms form over warm ocean waters and can cause devastating impacts when they make landfall. Understanding their characteristics and distribution is crucial for predicting their behaviour and preparing for their effects.
Key Definitions:
Tropical cyclones have different names depending on where they form. In the Atlantic and Eastern Pacific, they're called hurricanes. In the Western Pacific, they're typhoons. In the Indian Ocean and South Pacific, they're simply called cyclones.
Tropical cyclones require very specific conditions to form and develop. These natural weather systems don't just appear randomly - they need the perfect combination of atmospheric and oceanic conditions to get started.
For a tropical cyclone to form, several key conditions must be present simultaneously. Think of it like a recipe - miss one ingredient and the storm won't develop properly.
Ocean water must be at least 26.5°C to a depth of 50 metres. This warm water provides the energy needed to fuel the storm through evaporation.
Wind speeds must be similar at different altitudes. High wind shear tears apart developing storms before they can organise properly.
The storm must form at least 5° away from the equator so the Coriolis effect can cause the necessary rotation.
Tropical cyclones cannot form within 5° of the equator because the Coriolis effect is too weak to generate the spinning motion needed for cyclone development. This creates a "cyclone-free zone" around the equator.
Understanding the anatomy of a tropical cyclone helps explain how these powerful storms work and why they're so dangerous. Each part of the cyclone has distinct characteristics and plays a specific role in the storm's behaviour.
The eye is perhaps the most famous feature of a tropical cyclone. This circular area of calm weather sits at the storm's centre and can range from 10 to 65 kilometres in diameter. Inside the eye, winds are light, skies are often clear or partly cloudy and there's little to no precipitation.
The eye forms because air is sinking in the centre of the storm. As air descends, it warms and dries out, creating the calm conditions. The eye is surrounded by the most dangerous part of the storm - the eye wall.
The eye wall is a ring of towering thunderstorms that surrounds the eye. This is where you'll find the cyclone's strongest winds, heaviest rainfall and most severe weather conditions. The eye wall can extend up to 16 kilometres into the atmosphere.
Extending outward from the eye wall are curved bands of clouds and thunderstorms called spiral rain bands. These bands can stretch for hundreds of kilometres and bring heavy rain, strong winds and tornadoes to areas far from the storm's centre.
Tropical cyclones don't occur everywhere on Earth. Their distribution follows clear patterns based on ocean temperatures, wind patterns and the Coriolis effect. Understanding these patterns helps us predict where and when cyclones are most likely to form.
There are seven main ocean basins where tropical cyclones regularly form. Each basin has its own cyclone season and naming conventions.
Includes the Atlantic Ocean, Caribbean Sea and Gulf of Mexico. Hurricane season runs from June to November, with peak activity in August and September.
The most active basin globally, producing about one-third of all tropical cyclones. Typhoon season is year-round but peaks from July to October.
Extends from the Mexican coast to the International Date Line. Hurricane season runs from May to November with two distinct peaks.
Hurricane Katrina formed over the Bahamas and strengthened rapidly over the warm Gulf of Mexico waters. At its peak, Katrina was a Category 5 hurricane with winds of 280 km/h. The storm caused catastrophic damage along the Gulf Coast, particularly in New Orleans, where levee failures led to widespread flooding. Katrina demonstrated how tropical cyclone characteristics like storm surge and intense rainfall can combine to create devastating impacts.
Scientists use various scales to classify tropical cyclones based on their wind speeds and potential for damage. These scales help emergency services and the public understand the threat level posed by approaching storms.
Used in the Atlantic and Eastern Pacific basins, this scale categorises hurricanes from 1 to 5 based on sustained wind speeds. Each category represents increasing levels of potential damage and danger.
Category 1: 119-153 km/h winds - minimal damage. Category 3: 178-208 km/h winds - extensive damage. Category 5: 252+ km/h winds - catastrophic damage with complete roof failure and building collapse possible.
Different ocean basins use different classification systems. The Western Pacific uses a scale that includes tropical depressions, tropical storms, severe tropical storms and typhoons. The Australian region uses a similar five-category system but with different wind speed thresholds.
Tropical cyclone activity follows predictable seasonal patterns that vary by region. These patterns are driven by changes in sea surface temperatures, wind patterns and atmospheric conditions throughout the year.
Most cyclone basins have distinct peak seasons when conditions are most favourable for storm development. In the Northern Hemisphere, peak activity typically occurs from July to October, while Southern Hemisphere basins see peak activity from December to April.
Scientists are studying how climate change might affect tropical cyclone characteristics. While the total number of storms may not increase significantly, research suggests that the strongest storms may become more intense, with higher wind speeds and more rainfall due to warmer ocean temperatures and increased atmospheric moisture.
Tropical cyclones don't stay in one place - they move across ocean basins following predictable paths influenced by global wind patterns and pressure systems. Understanding cyclone movement is crucial for forecasting and warning systems.
Cyclones are steered by large-scale atmospheric patterns, particularly the subtropical high-pressure systems. In the Atlantic, hurricanes often follow a curved path northward and eastward as they encounter the westerly winds of the mid-latitudes.
Many tropical cyclones undergo recurvature, where they change from moving westward to moving northward and then eastward. This happens when storms move from the trade wind belt into the westerly wind belt of higher latitudes.