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examBoard: Cambridge
examType: IGCSE
lessonTitle: Global Distribution of Tropical Cyclones
Tropical cyclones are among the most powerful and destructive weather systems on Earth. These swirling storms bring intense winds, torrential rainfall and storm surges that can devastate coastal communities. Understanding where and when these storms form is crucial for disaster preparedness and environmental management.
Key Definitions:
Tropical cyclones don't form just anywhere. They need specific conditions:
Tropical cyclones typically form between 5° and 30° latitude north and south of the equator. They rarely form at the equator itself because the Coriolis effect is too weak there to generate the necessary spin. The specific regions where they develop are known as "cyclone basins" and have distinct seasonal patterns based on when ocean temperatures are warmest.
Tropical cyclones form in seven main basins around the world. Each basin has its own seasonal patterns and naming conventions. Understanding these patterns helps meteorologists predict when and where storms might develop.
Season: June to November (peak: August-September)
Areas affected: Caribbean, Gulf of Mexico, eastern United States, Central America and occasionally western Europe
Name used: Hurricanes
Averages 10-15 named storms annually
Season: Year-round (peak: July-October)
Areas affected: Philippines, China, Japan, Taiwan, Vietnam
Name used: Typhoons
The most active basin, averaging 25-30 tropical cyclones annually
Season: April-December (peaks: May and November)
Areas affected: India, Bangladesh, Myanmar, Thailand
Name used: Cyclones
Fewer storms but often very deadly due to dense coastal populations
Season: November-April
Areas affected: Australia, New Zealand, Pacific Islands
Name used: Cyclones
Averages about 10 tropical cyclones annually
Season: November-April
Areas affected: Western Australia, Indonesia
Name used: Cyclones
Typically affects less populated areas compared to other basins
Season: November-April
Areas affected: Madagascar, Mozambique, other East African countries
Name used: Cyclones
Can cause severe flooding in Madagascar and southeastern Africa
While the main basins account for most tropical cyclone activity, some unusual events can occur:
The South Atlantic rarely experiences tropical cyclones due to strong wind shear and cooler water temperatures. However, in 2004, Hurricane Catarina became the first recorded South Atlantic hurricane to make landfall, striking Brazil. This extremely rare event challenged previous understanding of where tropical cyclones could form.
Sometimes called "Medicanes," these are rare cyclonic storms with tropical characteristics that form over the Mediterranean Sea. While not true tropical cyclones, they can bring hurricane-force winds and heavy rainfall to countries like Greece, Italy and Turkey.
Tropical cyclone seasons follow predictable patterns based on sea surface temperatures and global wind patterns. Understanding these seasonal variations is crucial for disaster preparedness and resource allocation.
Tropical cyclones form when ocean waters reach temperatures of at least 26-27°C. As the sun's position shifts throughout the year, different ocean basins warm up and cool down, creating distinct cyclone seasons. Additionally, the monsoon trough (a zone of low pressure) shifts position seasonally, providing the initial disturbance needed for cyclone formation.
In the Northern Hemisphere, the peak season is typically late summer to early autumn (August-October) when ocean temperatures are warmest. In the Southern Hemisphere, the peak is during their summer months (January-March).
In November 2013, Typhoon Haiyan struck the Philippines as one of the strongest tropical cyclones ever recorded at landfall. With sustained winds of 315 km/h (195 mph), it devastated the city of Tacloban and surrounding areas.
Key impacts:
Haiyan formed in the Northwest Pacific basin during its typical season. The unusually warm ocean temperatures in the region contributed to its extreme intensity, highlighting how sea temperature anomalies can affect tropical cyclone strength.
As our climate changes, scientists are studying how tropical cyclone patterns might shift in the future. While there's still uncertainty, several trends are emerging from research:
Studying changes in tropical cyclone patterns is challenging because:
In March 2019, Cyclone Idai struck Mozambique, Zimbabwe and Malawi in the Southwest Indian Ocean basin. It was one of the worst tropical cyclones on record to affect Africa.
Key impacts:
Idai highlighted how tropical cyclones can affect regions with limited early warning systems and disaster response capacity. The storm's unusual strength for the region raised questions about whether climate change might be influencing cyclone intensity in the Southwest Indian Ocean basin.
Just as important as knowing where tropical cyclones form is understanding why they don't form in certain regions. Several factors prevent tropical cyclone formation:
This explains why regions like the South Atlantic, the eastern South Pacific and areas near the equator rarely experience tropical cyclones, while coastal regions in the tropics and subtropics must regularly prepare for these powerful storms.
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