There is one thing that is almost more certain than the queues at the toll booth on August 15th: the August 15th storm. Sudden thunderstorms, unseasonal hail, skies that turn black in a matter of minutes after days of scorching sun. A script that repeats itself every year with almost comical punctuality – except that, in recent years, these events are becoming more and more intense and less predictable. It’s (also) the fault of the changing climate.
What is the mid-August storm?
The “August storm” is neither an urban legend nor a coincidence: it is a real meteorological phenomenon, linked to the typical dynamics of the Mediterranean summer. After weeks of dominance by the African subtropical anticyclone – the one that brings heat waves with temperatures that touch or exceed 40°C – the system tends to weaken or move, leaving room for the entry of cooler Atlantic currents from the west and north-west.
The result? A violent thermal contrast between the scorching air accumulated on the ground and the colder air masses at altitude, which generates intense thunderstorms, often accompanied by hail, gusts of wind and localized downpours. Everything is concentrated statistically in the window between 15 and 20 August, even if in recent years the margins have become more elastic.
Why does it almost always arrive on August 15th?
The answer lies in the physics of the summer atmosphere. In August, the Mediterranean has accumulated months of heat: the sea is warm, the land is overheated, the air is full of humidity. When the African anticyclone – which for weeks has kept Atlantic disturbances at bay – begins to give way even only partially, the “cap” loosens and fresh fronts manage to penetrate towards the south.
The meeting between these two air masses, so different in temperature and humidity, is explosive, almost literally: storm cells of great intensity are formed, the so-called MCS (Mesoscale Convective Systems), which can dump an entire month’s rainfall on limited areas in just a few hours. The most exposed areas? The Alps and Pre-Alps first, then the Apennines, and often also the adjacent plains and the Tyrrhenian coasts.
How is this changing with the climate crisis?
This is where things get more interesting — and more worrying. The most recent studies, including those by the CNR-ISAC and the IPCC reports, confirm a clear trend: summer storms in Italy are becoming less frequent but more intense. Less moderate rainfall, more extreme events. In other words, the mid-August storm does not disappear, but transforms.
An analysis published on Nature Climate Change showed how the warming Mediterranean is increasing the energy available to convective systems, making summer storms potentially more violent. At the same time, the heat waves that precede them are increasingly longer and more intense: the African anticyclone has become more “muscular” and persistent compared to a few decades ago, which means that the contrast when it gives way is even more abrupt.
The practical result? Larger hailstorms, more concentrated storms, and greater difficulty in accurately predicting where and when they will hit.
Which areas are most at risk?
Italian geography plays a fundamental role. The areas historically most affected by the August 15th storm are:
Coasts generally fare better thanks to the mitigating effect of sea breezes — but they are not immune, especially when the phenomena are particularly intense.
What to do (and not do) during summer storms
Whether it is the classic mid-August storm or any storm, some basic rules always remain valid. Avoid staying under isolated trees or in exposed areas during lightning. Do not swim in the sea with thunderstorms approaching (electrical discharges spread through the water). Protect umbrellas and light objects which can become dangerous with gusts of wind. And, if you are in the mountains, descend into the valley before the afternoon: thunderstorms at high altitude form quickly and can surprise even the most experienced hikers.
How to follow weather warnings
The Ministry of Health’s alert system is active every summer from 25 May to 20 September, with daily updates (Monday to Friday) for 27 Italian cities. For specific weather alerts, the reference is the national Civil Protection alert system, which publishes bulletins for each region 24-48 hours in advance. Following these channels — especially in an increasingly unpredictable summer — is not paranoia: it’s common sense.
The usual recommendations for the heat that precedes storms remain valid: avoid direct exposure to the sun between 11am and 6pm, drink regularly, prefer light meals and pay attention to the elderly, small children and lonely people. The public utility number 1500 is also active every summer.
