In 2021, the world saw a rare and powerful weather event: two major cyclones, Seroja and Odette, collided and caused severe destruction in different parts of the world. Though they started in separate oceans, they came together off the western coast of Australia, creating devastating effects. This anomalous occurrence showed how unpredictable and powerful tropical storms can become when they interact.
Cyclone Seroja began in the Indian Ocean in April 2021 as a low-pressure system that quickly grew into a strong Category 3 cyclone. The storm brought heavy rainfall, strong winds, and widespread flooding to Indonesia, Timor-Leste, and Australia. Indonesia suffered the most damage, with flash floods and landslides killing over 170 people and displacing thousands. Although Seroja weakened as it moved toward Western Australia, it still caused significant damage to buildings and infrastructure.
Yetti Lekeama, one of the few survivors of Cyclone Seroja, said, “I didn’t know what to do and where to go. It’s completely dark. But I could hear the sound of the rooftop flying over my house, and breaking wood.”
Cyclone Odette, also called Typhoon Rai, was a powerful Category 5 typhoon that hit the Philippines and other Southeast Asian countries in December 2021 at its peak point. With winds reaching up to 270 km/h, Odette was one of the strongest storms of the year. It caused severe flooding, landslides, and power outages, killing over 400 people. Hundreds of thousands of people were displaced, and the storm’s damage cost billions of dollars. Odette formed near the coast of Western Australia, just northwest of Cyclone Seroja. Its quick development into a strong typhoon showed the strength of storms in the Pacific Ocean, a region already known for frequent cyclones.
“I am asking for prayers for my family. They are starving right now in the streets waiting for donations. Typhoon Odette washed away their house… My sister has lost hope; she began to walk into the ocean to die. Thank God that her son pulled her from the waters before anything worse could happen. Please pray for my family,” an ICM (International Medical Corps) staff said a few days after the cyclone.
Although Cyclones Seroja and Odette were separate storms, their paths and behaviors were linked in a rare meteorological event called “cyclone interaction.” This happens when two storms come close enough to influence each other. Even though Seroja formed in the Indian Ocean and Odette in the Pacific, their paths crossed in early 2021, with Seroja already active and Odette starting to form.
The storms’ close timing and location caused them to affect each other’s weather systems. Their overlapping winds and pressure systems led to unusual weather patterns in Southeast Asia, including stronger winds and heavier than expected rainfall.
To study the effects on the ocean, Dr. Oliver Wurl and Dr. Jens Meyerjürgens from the University of Oldenburg used satellite data, ARGO floats, autonomous drifters, and computer models. This data that they collected helped them understand things like water salinity and water temperature from the sea surface down to 2,000 meters.
Dr. Wurl explains, “Seroja first stalled the smaller cyclone Odette, then merged with it three days later. After merging, Seroja changed direction sharply by 90 degrees on April 9.” This event not only changed weather patterns but also caused a rare interaction with the ocean below.
The research showed that sea-surface temperatures dropped by 3°C after the cyclones merged, and cold water from deep in the ocean rose to the surface in a process called “upwelling.” This cooling effect was especially strong for the cyclones’ intensity. The highest wind speeds, about 130 km/h, were typical of a Category 1 cyclone. However, the cooling and upwelling usually happen in much stronger storms, like Category 4 or 5 cyclones.
To learn more about these interactions and their link to extreme weather, Wurl and Meyerjürgens will join a research expedition on the METEOR vessel next year to study the Mediterranean and subtropical Atlantic.