At the beginning of this week it was not in anyone’s plans the so-called extratropical cyclone will arrive in Santiago. What’s more, it was ruled out, attributing the climatic phenomenon to the south of the country.
However, as often happens in meteorology, the forecast changes day by day, often the weather is unpredictable. And everything indicates that this will happen again, since the latest projections maintain that Santiago would register precipitation during the weekend, and even during the course of next week.
The phenomenon, unusual in our country, began approximately Tuesday night with the first rainfall in the southern zone, which They would last for several more days.
Also called a gigantic cyclone, It occurs under an intense associated low pressure, also known in meteorology as a cyclone.
Raúl Cordero, climatologist at the University of Santiago, explains that an extratropical cyclone is basically a low pressure system that, as its name indicates, is located outside the tropics. Tropical cyclones are not necessarily rare, but in Chile we usually refer to them as frontal systems or simply storms.
“The intensity of cyclones depends on how low the pressure is at their core. If the pressure is very low, the winds can reach important cities. In the case of this particular cyclone, the pressures have not been extraordinarily low, therefore, the intensity of the associated winds does not exceed 80 km/h at sea,” adds Cordero.
Specifically, in the capital during the weekend (Saturday and Sunday), An estimated total of 15 mm would fall. And that would not be all, since on Wednesday a new frontal system would arrive, with more precipitation than the first, exceeding 20 mm of water fall (see graph below). Although the latter would correspond to another frontal system.
Cordero maintains that what has made this cyclone striking is its extension and persistence. It has been parked off the coast of south-central Chile for several days, with a diameter equivalent to the length of the national territory.
“An interesting characteristic of this low pressure system is that it has been able to drag several masses of humid air of tropical origin towards Chile, that is, the cyclone has been driving the arrival of atmospheric rivers to the country,” explains the climatologist.
Precisely, one of these atmospheric rivers is the one that has been present since last Wednesday, causing abundant rainfall with a relatively high zero isotherm in the south-central part of the country.
The one that will affect the central area during the weekend is the tail of this system, says Cordero. “Although there are still a few days left, the rainfall this weekend in the Metropolitan Region is not expected to be as intense as that recorded during the last two days in the south-central part of the country,” says Cordero.
The academic from the University of Talca, Patricio González, indicates that the phenomenon produces winds, as well as rain. “All the frontal systems that affect Chile bring an associated low pressure, it is not a hurricane or a tornado, because for this we need to have a warm sea, as is the case of the Tropical Atlantic Ocean.”
“We have, on our coasts, an ocean with colder temperatures, therefore the only thing that can generate a rain storm and wind”says González.
“The current system, fortunately, does not involve winds comparable to those of its tropical relatives,” establishes the climatologist from the University of Santiago.
Cyclones also receive surnames, says Cordero, depending on the geographical area in which they occur. “For example, there are tropical, extratropical or subtropical cyclones.”
“The tropical ones, in turn, also receive alternative names, depending on the basin in which they occur. Very intense tropical cyclones are known as hurricanes in the Atlantic and Eastern Pacific. These same systems are known as typhoons in the Western Pacific,” says the climatologist.
