Tropical cyclone season never ends

Tropical cyclones made quite a splash in 2024. Hurricanes Helene and Milton, which hit the southeast United States in September and October, were two of the biggest. However, while the Northern Hemisphere can relax a little in winter and spring, the Southern Hemisphere, on the contrary, has to get ready for the new cyclone season. Today, we will tell you what to expect from tropical cyclones in the next six months.

The major cyclones of 2024

Before moving on to the Southern Hemisphere, let’s return to the Northern Hemisphere again. Milton was probably the strongest hurricane of 2024, and unprecedented preparations were made for its arrival in Florida. A state of emergency was declared, more than 5 million people were evacuated, and apocalyptic footage of floods and winds of up to 80 m/s flew around the world. Milton became the record holder of the year not only for wind speed, but also for atmospheric pressure in the center: 897 hPa. Recall that the normal atmospheric pressure is 1013 hPa, and in cyclones of temperate latitudes, the pressure rarely falls below 970 hPa. The consequence of such low pressure was the extreme wind speeds.

Helene, the costliest hurricane of the year and the second deadliest storm to hit the United States in over half a century, hit the southern US just a week before Milton. The damage it caused was estimated at almost 113.5 billion dollars. While Helene was only a Category 4 hurricane with wind speeds of 225 kilometers per hour and 938hPa, the deluge of continuous rainfall over 4 days (more than 12 inches of rainfall in places) led to rivers overflowing their banks, mudslides, and entire mountain towns, neighborhoods, and roads being washed away or submerged—leaving over 230 dead. The deadliest typhoon in this season was Yagi, with more than 800 dead, affecting China, the north of Vietnam, and other countries of Southeast Asia.

Who tracks tropical cyclones?

While tropical cyclone tracking and warnings in the Gulf of Mexico are legitimately carried out by the U.S., things are not so obvious in other parts of the world. Despite this, the international community has been able to organize and develop a clear system.

Tropical cyclones almost always form in specific areas called «basins». To avoid chaos in making forecasts and warning people about the dangers, each basin is assigned a weather agency from one of the neighboring countries. Agencies from other countries can also monitor cyclones, but do not have extensive international responsibilities.

Tropical cyclone basins (highlighted in red) and the cities from which they are monitored. Source: Atlantic Oceanographic and Meteorological laboratory

There are three basins in the southern hemisphere: the southwestern Indian Ocean basin (figure 5 in the figure), the southeastern Indian Ocean basin (also called the Australian basin, figure 6 in the figure), and the South Pacific basin (figure 7). There is no basin in the southern part of the Atlantic Ocean because tropical cyclones are rare here, and do not need to be monitored closely.

In terms of when they occur, the tropical cyclone season in the southern hemisphere lasts from mid-November to the end of April. The greatest number of cyclones is usually observed in February and March, when the ocean is warmest.

What to expect from the 2024/25 season in the Australian Basin

The Bureau of Meteorology predicts that 9-10 tropical cyclones will form in the Australian Basin in the coming season, which is about normal. At the same time, abnormally high ocean temperatures are forecast, so the number of strong tropical cyclones may increase: usually there are 5, but this year there could be 7 or 8. About half of the tropical cyclones of the basin affect the western and northern coast of Australia, so the number of dangerous weather phenomena here may be higher than normal.

The Three Beams Monument in Darwin, Australia. These huge metal structures were bent by Tropical Cyclone Tracy in 1974. Photo: Bidgee / Wikimedia

By the way, an interesting fact! Only an authorized meteorological agency in each basin can assign a name to a cyclone, and all agencies prepare lists of names in advance. For example, the first tropical cyclone of the Australian region in the season 2024/25 will be named Robin, followed by Sean, Talia, Vince. But the logic of names is different for each agency. For example, the U.S. has compiled 6 lists of names for most (21) letters of the alphabet and consistently names hurricanes with A, B, C and so on. Every 6 years, hurricane names are repeated, except for particularly strong and significant hurricanes, which are permanently assigned a name and removed from the list (e.g., Katrina). The Japan Meteorological Agency has several lists for each year, depending on the specific location where the typhoon will appear.

The 2024/25 season in the Indian Ocean

Tropical cyclones in this basin are monitored by Météo-France, headquartered on Reunion Island. Between 11 and 13 tropical cyclones per season are forecast, which is much higher than normal (about 9 per season). This is primarily due to abnormally high air and ocean temperatures. Interestingly, the meteorological agency of Mauritius, which is often in the zone of tropical cyclones, forecasts rainfall amounts much lower than average (80-85% of the norm). It can be assumed that either the intensity of tropical cyclones will be lower than usual, or they will have non-standard trajectories and bypass some islands.

Tropical cyclone Manou passes over Madagascar, 2003. Source: Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC

By the way, as early as mid-November, even before the official start of the season, a Category 4 tropical cyclone named Becky formed in the southern Indian Ocean! Fortunately, it did not cause any damage, and weakened before approaching the first islands.

The South Pacific Ocean season in 2024/2025

Tropical cyclones in this basin are monitored by the Fiji Meteorological Service. Tropical cyclone activity is forecast to be close to normal this season. For New Caledonia and Vanuatu, the probability of tropical cyclones is assessed as average, and to the east (Fiji, Tuvalu, Tonga), it is expected to be below average. A total of 6-9 tropical cyclones are expected in this basin, with 5-6 of them being strong.

Waves raised by Tropical Cyclone Vania in the Vanuatu Islands in 2011. Source: Graham Crumb

We will soon find out if these predictions will come true. For now,the main goal of the predictions is to protect human lives. Take care of yourselves, and let’s keep an eye on the weather together!

Text: Eugenio Monti, a meteorologist and a climatologist

Cover photo: Victor Rosarior / Unsplash

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