Astronomical autumn is now upon us: the autumnal equinox will arrive on September 23, but the change of season will not be immediate across the entire Peninsula. In the next few days, in fact, Italy will experience a transition phase, with a first taste of autumnal weather especially in the north-eastern regions, while elsewhere the heat will remain for a few more hours.
The change will be determined by a descent of cooler air coming from Northern Europe and Scandinavia, linked to a deepening depression structure. The first sector to be affected will be the North-East, where a clear drop in temperatures will be noticed from the early hours of Tuesday 22 September.
The refreshment reaches the Adriatic, the heat resists on the western side
The refresh will not involve all of Italy at the same time. The regions overlooking the Adriatic will be among the most exposed to the entry of northern winds, capable of causing a sharp drop in temperatures. In some locations the drop could even be close to 10 degrees compared to previous values, especially compared to the very hot phase that has just passed.
The situation is different on the Tyrrhenian and western sector of the Peninsula, where the mild air will manage to maintain conditions that still have a summer feel. Sardinia will also see a more gradual reduction in heat compared to the areas most exposed to cool winds.
Overall, therefore, the equinox will coincide with a first reduction in temperatures, but without an abrupt transition towards winter cold.
Western Europe remains under the dominion of high pressure
The atmospheric configuration of the next few days will be characterized by an interesting contrast: while part of central-eastern Europe will receive cooler air, the western part of the continent will remain protected by a vast anticyclonic field.
On the Iberian Peninsula, in particular, high pressure will maintain conditions much more similar to summer, with temperatures still high even in the following days. A mass of warm air will then tend to stretch towards France and Germany, without however directly involving Italy in the first phase.
Mid-week with thunderstorms especially in the Centre-South
Atmospheric instability could increase between the second part of the week. Some areas of the Peninsula could be affected by the passage of disturbed nuclei capable of generating thunderstorms.
The areas most affected could be the South, with particular attention to Sicily, while Northern Italy and Sardinia could remain more on the margins of the phenomena.
However, this will be a phase to be monitored, because the trajectory of the unstable currents could undergo changes in future updates.
End of September: possible new temperature rise in the North
Towards the last days of September, between the 28th and 29th, the scenario could change again. A new return of hot air from France could especially affect the northern Italian regions, bringing temperatures back to milder values.
At the same time, however, a presence of colder air will continue to remain active between Russia and Scandinavia, ready to attempt new incursions towards Western Europe.
Furthermore, in the nearby Atlantic, deep depressions with cold air at high altitude could form, but at the moment this dynamic seems destined to remain confined above all to the oceanic areas and the British Isles.
Towards October: high pressure still protagonist, but something could change
The beginning of October could still maintain characteristics that are far from a truly disturbed autumn. In fact, high pressures will continue to dominate much of the European continent, hindering the arrival of classic organized Atlantic disturbances.
However, some signs suggest possible changes. Instability could develop between the Iberian Peninsula and the western Mediterranean, while cooler currents coming from the Balkans could favor the formation of a depression over the Ionian Sea, with possible thunderstorms between Greece, Sicily and the Italian Ionian areas.
For now, therefore, the picture remains that of an autumn that proceeds slowly, still conditioned by the presence of many anticyclonic areas.
No wave of frost in Italy: the cold will remain further east
In recent days, hypotheses have circulated of an alleged arctic cold wave headed towards Italy, but the scenario predicted by meteorological models does not support a winter outbreak on the Peninsula.
The coldest air will remain mainly concentrated between Scandinavia, the Baltic countries, Poland, Ukraine and the Balkans, where the arrival of very low values at altitude will be normal for the period.
To bring a true Arctic influx to the Mediterranean, a much more complex configuration would be needed, with a strong expansion of the Azores anticyclone towards high latitudes, capable of favoring the descent of the freezing air towards the south.
In September, a dynamic of this type is decidedly less frequent than in the winter season.
Italy between cool climate and first signs of autumn
The period between 22nd and 24th September could represent the first real transition towards more autumnal conditions from a thermal point of view.
Temperatures could drop to lower values, with maximums generally below 24 degrees in many areas and minimums locally below 15 degrees.
The Adriatic regions will probably be the most exposed to fresh winds from the Balkans, with the possibility of some local showers or thunderstorms.
No early winter, therefore, but a first concrete sign of the seasonal change: summer will not disappear completely, but the atmosphere will gradually begin to take on characteristics closer to autumn.
