Autumn equinox with temperature drop and yellow alert in the South

The Autumn Equinox, occurring today, September 23rd at 02:05, officially marks the beginning of the new season, accompanied by an immediate shift in weather. Cool northeasterly currents have already caused a drop in maximum temperatures, estimated between 3 and 4°C in the North and along the Adriatic, bringing values in line with the seasonal averages.

On the weather front, cool air at higher altitudes is favoring the formation of local thunderstorms over Calabria, eastern Sicily, and Cilento. Civil Protection has issued a yellow alert for hydraulic, hydrogeological, and thunderstorm risks in various areas of Sardinia, Calabria, and Sicily. Over the rest of the country, sunny weather prevails with mild temperatures along the Tyrrhenian coast.

Forecasts indicate that between the evening of Thursday and Friday, September 25th, a core of cool North European air will pass through, bringing instability along the Adriatic coast down to the South, with rain and thunderstorms of moderate intensity and strengthening winds.

The autumnal equinox is the astronomical moment when the Sun is at the zenith of the Earth's equator, resulting in equal length of daylight and darkness across the entire planet. This year, this astronomical transition coincides with a significant change in the general atmospheric circulation, marking the end of the stable dominance of high pressure that characterized the end of summer.

The current situation arises from the partial westward retreat of the anticyclone, which has allowed cooler air to infiltrate from the Balkans into Italy. This process began on Tuesday, September 22nd, and initially caused a temperature drop concentrated in the Po Valley and the Adriatic sector, later extending to the entire peninsula. Temperatures fell by several degrees compared to the recent peaks, temporarily even dropping below the climatic average.

The next step will be the passage of a disturbance (the fourth of the month) which on Friday will mainly affect the Central-South, before giving way to a widespread return of sunshine over the weekend. However, the extensive clear skies at night will keep minimum temperatures low, which in the central valleys and the Po Valley could drop below 10°C.