Cyclonic Trajectories Defying Traditional Models

Cyclones no longer strictly follow the classic parabolic movement model, where they form in the northeast and gradually head towards our region. Vassen Kauppaymuthoo emphasizes that current climatic conditions now allow cyclones to form virtually anywhere, including areas previously deemed unusual, such as the Mozambique Channel. The cyclone Garance exemplifies this new reality: it developed rapidly and surprised many with its sudden intensification.

A cyclone formed further away, such as in the Australian region or towards the Chagos Archipelago, would have given meteorologists and authorities a more comfortable timeframe to anticipate its arrival and refine forecasts. However, the staggering speed at which some cyclonic systems can now evolve poses a significant additional danger. The recent example observed after Garance's passage near La Réunion is particularly telling: a violent wind rose suddenly, demonstrating how small cyclonic systems can transform into extremely dangerous phenomena in a very short time. These systems can indeed generate gusts reaching 200 km/h within just a few hours, drastically reducing the time available for organizing necessary preparations.

While Mauritius was relatively spared by cyclone Garance this time, a fundamental question remains: how long will this favorable situation last? Climate change significantly influences global atmospheric circulation, fundamentally challenging historical models that previously allowed for reliable cyclone trajectory predictions. Vassen Kauppaymuthoo explains this phenomenon, emphasizing that the presence of anticyclones or cooler air masses can now cause a rebound effect in cyclones, significantly diverting them from their initially anticipated paths.

The role of Antarctica in these atmospheric transformations is also receiving particular attention from the scientific community. Most anticyclones originate in this southern polar region, characterized by areas of high atmospheric pressure. Therefore, it is essential to study how these atmospheric upheavals influence and alter cyclone behavior. Although science cannot yet provide definitive answers to all these questions, it now seems clear that the complex interactions between cyclones and anticyclones, between the South Pole and the intertropical convergence zone located to the north, play a decisive role in the evolution of these extreme weather phenomena.

A Real Danger Not to Underestimate

Oceanographer Vassen Kauppaymuthoo firmly warns against an excess of confidence that could prove fatal: Mauritius is absolutely not indefinitely sheltered from the potentially devastating consequences of cyclones. "The danger lies in indulging in an illusion of safety," he cautions. He expresses satisfaction with the Mauritius Meteorological Services (MMS) decision to prioritize precautionary measures during Garance's passage, rather than unnecessarily jeopardizing lives by maintaining normal school and work activities.

Had Garance deviated, even slightly, from its trajectory, the consequences for Mauritius could have been significantly more severe. While some economic sector actors lament the financial losses incurred due to mandated days off, Vassen Kauppaymuthoo insists that the absolute priority must always remain the safety of the population. "There could have been loss of life, as seen in La Réunion. That has no price. Before brandishing figures, one must reflect, for the country truly escaped a disaster," he emphasizes.

Having not experienced the impact of a major cyclone since 2002, many Mauritians tend to dangerously underestimate the destructive power of these natural phenomena, which are among the most devastating natural disasters in terms of energy released. "When a danger of this magnitude presents itself, one must remain cautious and take necessary measures. This is not a game," insists the oceanographer, thus reminding us of the vital importance of a cautious approach to these extreme manifestations of nature.

Meteorology, a Complex Science

Contrary to popular belief, meteorology is not limited to simple sky observation, but is a rigorous science based on concepts and physical laws, mathematical equations, and analytical data integrated into increasingly precise numerical models. Observations come from sophisticated instruments such as radars, satellite images, and measurements of multiple atmospheric parameters, like pressure and temperature. This is what Ram Dhurmea, a meteorology expert, explains.

Before the advent of numerical models, observations were made using manual, analog, and mechanical measuring instruments. Today, supercomputers solve complex physical and mathematical equations to predict weather evolution with significantly increased accuracy, he notes.

"The differences between numerical models can be explained by the mesh resolution used, the data update frequency, and the quality of the initial information fed into the models," he adds. Ram Dhurmea also emphasizes the crucial importance of model validation. "If a model has not been validated before use, a meteorologist has a high chance of failure in their predictions, as one cannot use it blindly."

Nevertheless, despite all the technological and numerical advancements made, meteorology remains an imprecise science.

How a Cyclone Forms

According to Ram Dhurmea, a cyclone forms when winds from opposite directions meet, for example, when a west wind encounters an east wind, creating a vortex. The stronger the flow and speed of the wind, the more powerful this vortex becomes. This phenomenon leads to the convergence of air masses and the formation of clouds that amplify with oceanic moisture, giving rise to a depression.

If the conditions at altitude are favorable, the system intensifies. Conversely, wind shear can hinder its development. The trajectory of a storm is determined by currents at both high and low altitudes, depending on the system's intensity: a weak storm will be guided by low-altitude flows, while an intense cyclone will be influenced more by high-altitude flows. The thermal energy of the ocean can also play a significant role in the formation and trajectory of a storm.

It is important to note that currently, predicting a storm's trajectory remains a major challenge for researchers.

Glossary

• Strong wind: wind speed of at least 40 kilometers per hour and gusts of at least 90 kilometers per hour;
• Gust: surface wind with a recorded or expected speed.
• Heavy rain: downpours resulting in at least 25 millimeters of rain in 30 minutes.
• Torrential rains: weather conditions resulting in at least 100 millimeters of widespread rain that may last several hours.
• Tropical depression: meteorological phenomenon where the average wind speed is estimated at least 51 and at most 62 kilometers per hour.
• Moderate tropical storm: tropical depression system where the average wind speed is estimated at least 63 and at most 88 kilometers per hour.
• Intense tropical storm: tropical depression system where the average wind speed is estimated at least 89 and at most 117 kilometers per hour.
• Tropical cyclone: tropical depression system where the average wind speed is estimated at least 118, but not more than 165 kilometers per hour.
• Intense tropical cyclone: tropical depression system where the average wind speed is estimated at least 166 and at most 212 kilometers per hour.
• Very intense tropical cyclone: tropical depression where the average wind speed is estimated to exceed 212 kilometers per hour.
• Storm surge: difference between the actual water level caused by a weather disturbance and the level that would have been reached in the absence of the weather disturbance.
• Swell: system of ocean waves raised at a certain distance above the ocean due to winds blowing over that area.

The Cyclone Formation Cycle

1. Warming of Ocean Waters
   The process begins when ocean water reaches a temperature exceeding 26°C. This heat is fundamental as it provides the energy necessary for cyclone formation. Without this warm surface water, the cyclone could not develop.

2. Evaporation and Cloud Formation
   Ocean heat causes intense evaporation of water. This water vapor rises into the atmosphere, where it condenses to form clouds. This process releases latent heat, which is crucial as it acts as a thermal engine to fuel the system.

3. Tropical Depression
   When enough warm, moist air rises, atmospheric pressure decreases near the ocean surface, creating a depression. At this stage, winds begin to organize and rotate around the center of low pressure, but their speed remains below 63 km/h. This marks the beginning of the system's rotation.

4. Tropical Storm
   If conditions remain favorable, the depression intensifies. Winds accelerate to between 63 and 118 km/h. The rotation becomes more evident, and the structure of the system becomes more organized. At this stage, the storm usually receives a name.

5. Cyclone Formed
   When winds exceed 118 km/h, the tropical storm officially becomes a cyclone. Its structure is now well-defined, with a calm central eye surrounded by an area of violent winds and intense precipitation. The cyclone is now a powerful and autonomous meteorological system.

Tropical cyclones are called different names depending on the regions of the world:

• Hurricanes in the Atlantic and Eastern Pacific,
• Typhoons in the Western Pacific, and
• Cyclones in the Indian Ocean and Southern Pacific.