The Curious Phenomenon of Spain’s ‘Summer of San Miguel’
Spain is currently experiencing an intriguing climatic phenomenon . Without any advance warning or apparent cause, the thermometers have shot up, registering temperatures significantly higher than normal for this time of year. As we move into late September 2025, according to AEMET, we can expect a resurgence of warmer weather known as the “temperature rebound.”
What is the ‘Summer of San Miguel’?
This warm spell, colloquially referred to as Veranillo de San Miguel or Membrillo , typically graces the end of September and early October. Named after the festival of San Miguel celebrated on September 29, this period surprisingly represents a segment of good weather and elevated temperatures.
The Controversy of Existence
But what’s fascinating is that the phenomenon itself is often said to lack a scientific basis. In reality, claims about the Veranillo de San Miguel can be misleading. As we uncover the science behind it, we find that there is a clear explanation for why these “summers” have been occurring for the last three decades. For just a couple of days, temperatures rise above their historical averages as September winds down.
In fact, these fluctuations don’t even require substantial increases in temperature. A slight uptick is sufficient to prompt discussions about the Veranillo de San Miguel , treating it almost as another season.
The Science Behind the ‘Summer of San Miguel’
The phenomenon can often be attributed to a strong confirmation bias affecting popular meteorology. As noted in various studies, we have a propensity to “favor, search, interpret, and remember information that confirms our pre-existing beliefs.” This cognitive bias means that when two or three days of warmer temperatures appear at the end of September, they reinforce the perception of a “summer” period, even if the specifics are inconsistent.
Essentially, we observe a regularity in this phenomenon simply due to its high probability. Most years, a warm stretch occurs during this time, aligning with popular sentiment, even when actual temperatures may not consistently reflect traditional summer ranges.
What Lies Ahead?
So, will there indeed be a “summer” this year? The answer is a resounding yes . Just before the anticipated arrival of Hurricane Gabrielle, which is set to make landfall in the west of the Iberian Peninsula, Spain will be graced with a warm and stable weather system. An idyllic setting to wrap up the summer season.
However, what follows is a stark transition. Traditionally, the advent of autumn brings with it a sense of instability . The impending arrival of a hurricane only compounds this notion, emphasizing that summer is concluding, and the days of warmth are fleeting.
A storm brewing on the horizon reinforces the uncertainties typically associated with fall, ultimately marking a significant shift in weather patterns.
Image credit: ECMWF
This year, as we witness the arrival of the ‘Summer of San Miguel’, it serves as a reminder of the intricacies of our weather systems. While it represents a delightful respite at summer’s end, it also highlights the unpredictability that autumn can bring. Being aware of these cyclical patterns can help us prepare for what lies ahead, enhancing our understanding and appreciation of Spain’s diverse climate.