A cyclone will isolate itself in the seas around Italy, bringing widespread bad weather conditions to the centre-south. Sliding southwards, between the island of Pantelleria and the nearby Tunisian coast, over a stretch of sea that is still quite warm, the cyclone could evolve into a subtropical system.
As we saw yesterday, in this itemthe week will open under the banner of bad weather, due to the sinking into the central Mediterranean basin of a depression of Arctic origin, which in its terminal part it will rapidly evolve into a young “cut-off” on the lower Tyrrhenian Sea.
This time the bad weather will mainly affect the central-southern regions, only glancingly affecting the North and the central regions, especially the Adriatic sectors, due to the call of sustained and cold bora winds from central-eastern Europe, which will cause a consequent decline of temperatures.
Bad weather, even intense, in the South
During tomorrow evening, Tuesday 21 Novemberthe sinking of this extensive Arctic trough, towards the Tyrrhenian Sea, will favor the isolation of a young cyclogenesis, between Corsica and the waters of the middle Tyrrhenian Sea.
A turbulent week awaits us with bad weather, strong winds and the first cold wave of the season
The development of this depression will be favored by the eastward push of the high pressure of the Azores, which will push a wedge in the direction of Germany and Poland, thus cutting the sagging axis in its southernmost part, up to the isolation of the extratropical cyclone on the central Tyrrhenian Sea.
Such depression among Wednesday 22nd and Thursday 23rd will slip towards the Sicilian Channel, where a new intense advection of vorticity at high altitude, triggered by the interaction between the polar jet stream and the sub-tropical one, will evolve into a new deep cyclogenesis which will pass near Sicily, bringing bad weather, even severe .
There is also a risk of thunderstorms and local storms on the island, especially in the southern and eastern sectors. For Sicily it will be the first real “anti-drought” disturbance of the season, given that the heaviest rainfall this time will hit the south-eastern part of the region, in particular the Iblei area, hard hit by the drought.
There are places between Agrigento, Nisseno, Ragusa and Syracuse, which have not seen a single drop of water for months.
In addition to Sicily, where the phenomena will become more intense and widespread, the rains and showers between Wednesday and Thursday will also hit Calabria and Puglia, where sustained northerly winds will blow.
Risk of “tropical transition” on the Sicilian Channel?
Analyzing the latest releases of mathematical models highlights the possibility of witnessing one “tropical transition” of the minimum that will isolate itself on the Sicilian Channel, between Wednesday and Thursday.
In fact, with the sliding of the depression towards the south, between the island of Pantelleria and the nearby Tunisian coast, on a stretch of sea that is still rather warm on the surface (values around +22°C +23°C), we could witness a process of “warm seclusion”.
This process occurs when the retreat of the warm front and pre-frontal warm air, associated with it, on the post-frontal sector, leads to the isolation of a vast bubble of warm air, which is surrounded along its sides by the cold post-frontal air masses, dominant on the western and northern sector of the extratropical cyclonic circulation.
This results in the isolation of a core of hot air right near the minimum depression, causing the system to take on typical “hybrid”, sub-tropical, or in the most relevant cases more specifically tropical, characteristics.
Risk of a “Medicane”?
In this case the depression, already by Friday 24th, could evolve into a hybrid cyclone of a subtropical character. A TLC (remember it is an acronym for tropical like Cyclone), with the “hot heart” appearing only in the lower layers (850 hPa), while at higher altitudes colder air still prevails, even if during the evolution of the “tropical transition” the “warm heart” can expand and extend upwards (up to 700 hPa).
Furthermore, some models see how a core of positive vorticity (very high values) in the middle troposphere (500 hPa) would match perfectly with the minimum (and the eye) of the depression circulation. A characteristic of hybrid, or more tropical, systems.
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In more strictly tropical cyclones the convection is much deeper, with imposing thunderstorm cumulonimbus clouds that can easily exceed 14 km in height, given the greater quantity of latent heat absorbed by the sea surface, in an environment that is already very humid in the lower layers.
The one expected between Thursday and Friday, however, should not deepen in such a way as to reach the status of “medicane”, yet it will produce very strong winds, especially on the Sicilian Channel, with speeds up to over 80/90 km/h, as highlighted by the meteored reference model.
The kinetic energy of the wind will transfer to the sea, raising an impressive wave motion, with waves even more than 3/4 meters high between the upper Sicilian Channel and the westernmost sector of the lower Tyrrhenian Sea.
What risks for Sicily?
Everything will depend on the exact trajectory that this cyclone will follow, immediately after the hybridization phase. If it passes near Sicily, the island risks having to deal with a severe phase of bad weather, especially in terms of heavy rainfall, thunderstorms and very strong winds from the eastern quadrants.
The most affected areas should be those of the southern coast and the entire eastern sector, from Capo Passero to Fiumefreddo and Taormina, where rainfall could persist until Friday.
On Etna it will snow again heavily on the summit area, although initially starting from 2000 metres, with snow levels that could drop lower between Thursday and Friday, when slightly colder air, under the pressure of intense easterly and northerly winds, could reach Sicily, bringing about a decrease of temperatures.
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In particular, the south-eastern area of Sicily could see the encroachment of the storm bands rotating on the left quadrant of the sub-tropical depression, with consequent rainfall accumulations even in three figures.
