What is Tropical Cyclone Sean, a Category 3 Storm Emerging in Australia? Causes, Impact, and Path Explained

Tropical Cyclone Sean is a significant weather event currently affecting Western Australia. As of January 2025, it has intensified to a Category 3 system and is expected to weaken further as it moves southwest into cooler waters off the coast.

This tropical cyclone reached Category 4 strength but has since been downgraded to Category 3 as of the latest updates. It is expected to weaken further and drop below tropical cyclone strength by January 22, 2025.

Additionally, significant rainfall has been recorded, particularly in Karratha, which experienced its heaviest daily rainfall on record at 274 mm within 24 hours. This has led to flooding in some areas.

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Causes of Tropical Cyclones

Tropical cyclones, including Sean, typically arise due to several key atmospheric and oceanic conditions:

• Warm Sea Surface Temperatures: Cyclones form over warm tropical oceans where sea surface temperatures exceed 27 °C, providing the necessary heat and moisture for storm development.
• Coriolis Force: This force is crucial for the rotation of the cyclone, helping to organise the storm system.
• Low-Pressure Area: A pre-existing weak low-pressure area or cyclonic circulation is essential for initiating cyclone formation.
• Vertical Wind Shear: Minimal variations in vertical wind speed contribute to the stability and growth of the cyclone.

Formation of Tropical Cyclone Sean

Tropical Cyclone Sean began as a tropical disturbance and intensified over warm waters. 

It formed on January 20, 2025, as a Category 1 cyclone, quickly escalating to Category 4 due to favourable conditions. The cyclone's structure includes:

• Eye and Eyewall: The eye is characterised by calm weather and low pressure, while the eyewall contains the strongest winds and heaviest rainfall.
• Updrafts and Moisture: Rising moist air forms clouds, leading to the storm's development. The system relies on continuous warm air rising from the ocean surface.

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Effects of Tropical Cyclone Sean

The cyclone has had notable effects on the regions it impacted:

• Heavy Rainfall: Karratha reported its highest daily rainfall on record at 274 mm, leading to localised flooding.
• Flooding Risks: The Bureau of Meteorology (BoM) warned of flash flooding due to intense local rainfall, prompting emergency alerts for residents along the Pilbara Coast.
• Infrastructure Impact: Floodwaters affected roads and homes, although overall damage has been minimal since Sean did not make landfall directly on the coast.

Impact on Communities

Flooding and Disruptions: The cyclone has caused substantial disruptions, particularly in towns like Karratha and Exmouth. Emergency services have responded to numerous incidents related to flooding, including water rescues and power outages affecting hundreds of residents.

Infrastructure Challenges: Floodwaters have affected roads, with some routes closed due to inundation. The North West Coastal Highway remains open, but with caution advised.

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Safety Measures

Authorities have urged residents to remain vigilant and prepared for potential impacts from the cyclone's unpredictable nature. Emergency services are actively monitoring the situation and providing assistance where needed.

Current Updates (as of January 21, 2025)

Current Status: As of January 21, Sean has downgraded to a Category 3 system and is expected to weaken further as it moves southwest into cooler waters off the coast. It may drop below tropical cyclone strength by January 22.

Movement: The cyclone is approximately 400 km offshore and poses no direct threat to the mainland at this time.

Future Outlook: No additional cyclones are forecasted in the immediate future within Australia’s region, indicating a potential stabilisation in weather conditions following Sean's passage.

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