Why do we speak of a “former hurricane” for the weather phenomenon which will affect France this week?

Kirk arrives in France. But what are its characteristics of the one that was recently a hurricane? And why do we speak of a “former hurricane”? In what forms will it reach France? Guillaume Jauseau, meteorologist at Météo & Radar, answered these questions to 20 Minutes.

What are the characteristics of Hurricane Kirk?

Category 2 Hurricane Kirk formed on September 29 near Cape Verde. It intensified rapidly, reaching category 4 – out of 5 – with gusts of up to 250 km/h and becoming the third major hurricane of the season in the North Atlantic. Fortunately, he hasn’t done any damage yet.

Beyond these aspects, it is a “very normal” cyclone, with tropical characteristics, that is to say, a warm heart, symmetry with an eye.

Why should we no longer talk about a hurricane when Kirk hits France?

Kirk is moving northwards and is beginning an “extra-tropical” transition. This is why we speak of “ex-hurricane” to talk about the phenomenon when it hits the territory. And this is what happens to all the hurricanes that arrive in our latitudes.

In summary, they lose a very large part of the tropical characteristics upon contact with more temperate waters, becoming “typical mid-latitude” depressions. The latter have a cold heart, they feed on high altitude winds, for example.

In what forms will it reach France?

Kirk will therefore reach its mature stage of “extra-tropical storm” just before hitting the French coast, at the end of the day on Wednesday. She must cross France the next day, then she will reach the Benelux in the days that follow. In France, we expect gusts, up to 140 to 160 km/h, heavy rain and strong swells although the coefficients are not significant, which makes the risk of submersion less. These scenarios are still to be refined.

But we know that Kirk will be at the origin of a significant transport of water vapor over the Atlantic and will generate an atmospheric river, thus increasing the risk of heavy precipitation. This is often the case in these depressions which come from the tropics. They feed on humidity and water vapor and are still full of it when they arrive on our coasts.

Do these types of events happen often in France?

It’s always existed. Extra-tropical storms represent the end of the life of each hurricane. It happens very often but as they arrive very weakened, we don’t even realize it. Besides, this Kirk storm is quite typical for the season.

In terms of scientific consensus, the number of storms has not significantly increased. Trends vary by region, with fluctuations observed in parts of the North Atlantic without a clear upward trend. In Europe, we have already experienced this with Ophelia in 2017 or with Debbie in 1961, which caused more than 60 deaths.

What are the links between this type of meteorological episode and global warming?

Global warming has no direct impact on the frequency of extra-tropical storms in particular. But because of climate change, the oceans are warmer, they release more water vapors into the atmosphere and these storms, feeding on these water vapors, will then dump a lot more rain. On the other hand, there is an increase in the number of category 3, 4 and 5 hurricanes, therefore the most violent.