We explain why Hurricane Milton went from category 5 to 1 in a few hours

After crossing Florida, Milton will continue his journey and, eventually, die in the Atlantic. Arriving from the Gulf of Mexico, the hurricane made landfall on the night of Wednesday October 9 to Thursday October 10, before being quickly downgraded in the early morning, from category 3 (out of the 5 on the Saffir scale). Simpson) to Category 2, then Category 1, by the US Hurricane Center (NHC). Milton, which reached the west coast of Florida on Wednesday evening “near Siesta Key, Sarasota County”, with winds reaching 165 km/h, still recorded peaks of up to 140 km/h Thursday morning, continues the NHC.

While its rapid intensification during the day on Monday had left meteorologists speechless, even on the verge of tears (as in this video on X), the loss of power of hurricanes as they approach the coast is a normal phenomenon. “The cyclones [le même phénomène, mais dans l’océan Indien ou le sud-ouest du Pacifique] weaken rapidly as they penetrate inland, where they are no longer supplied with hot water”, explains Météo-France. Because, as we recall the organism, for a cyclone to develop, “the temperature of the ocean must be high in the first 60 meters to allow intense evaporation, therefore a transfer of humidity from the ocean to the atmosphere”.

Just as a hurricane gains power as the waters warm, it logically weakens when it meets dry land, because it is deprived of its fuel.

But be careful, “it sometimes happens that a powerful cyclonic phenomenon can survive its passage over the land and regain energy upon contact with water” after encountering an island or, as here, a peninsula, recalls the government portal Georisks. The American National Center for Oceans and Atmosphere (Noaa) declared Thursday morning on X that Milton was still a hurricane after its passage over Florida. Trees uprooted, roofs torn off, streets flooded… Although weakened, it was devastating during its passage, notably depriving more than three million homes of power.

And if it moves again towards the Atlantic, now moving this time from west to east. Milton may only finally dissipate into a storm or depression once it comes into contact with colder waters.

Furthermore, a rapid downgrade in its power on the Saffir-Simpson scale does not mean that a hurricane becomes harmless. A specialist in these phenomena at the University of Arizona, Kim Wood notes, on “all hurricanes are different”, “a weakening hurricane does not mean its impact will be minimal”. In 2005, Hurricane Katrina, one of the deadliest and most destructive in recent United States history, also quickly went from category 5 to category 3 before hitting Louisiana, recalls the expert.

Finally, the Saffir-Simpson scale classifies phenomena according to the recorded wind power, which does not provide information on expected precipitation on land. “A powerful cyclone can cause very little precipitation and vice versa,” thus qualifies Georisks, revealing that “the quantity of water depends on the size and structure of the clouds making up the cyclone system, its speed of movement as well as its trajectory”.

Quoted by AFP, Professor John Marsham, specialist in atmospheric sciences, finally recalls that climate change, by warming the seas, makes the rapid intensification of hurricanes more likely, but also the risk that they will be particularly rainy: “Warm air holds more water, causing heavier rain and more flooding,” he explains. Worse, at the same time, “Sea level rise due to climate change leads to worsening coastal flooding,” continues the climatologist.

While the rate of ocean warming has almost doubled since 2005, according to a recent study by the European Copernicus Observatory, the rains and winds of Hurricane Helene, which devastated the southeast of the United States at the end of September and caused more of 230 deaths, were thus made approximately 10% more intense by climate change, a study by World Weather Attribution (WWA) showed on Wednesday. Water temperatures in the Gulf of Mexico, where Helene formed, were about 2°C above normal, record temperatures made 200 to 500 times more likely by climate change. One of the authors of the study, climatologist Ben Clarke, then warned: “If humans continue to burn fossil fuels, the United States will face even more destructive hurricanes.” Milton, and those who succeeded him.

Since the 19th century, the average temperature of the Earth warmed by 1.1°C . Scientists have established with certainty that this increase is due to human activities, which consume fossil fuels (coal, oil and gas). This warming, unprecedented in its speed, threatens the future of our societies and biodiversity. But solutions – renewable energies, sobriety, reduced meat consumption – exist. Discover our answers to your questions on the climate crisis.