Spain enters astronomical autumn with forecast temperatures reaching 38°C

Summer heat overlaps with the autumn equinox

The astronomical arrival of autumn in Spain on Wednesday, 23 September 2026, coincides with widespread late-season heat rather than cooler seasonal weather. Spain's state meteorological agency, AEMET, expects daytime temperatures to sit between 5 and 10 degrees Celsius above seasonal averages across most of the country, with certain northern districts exceeding normal levels by more than 10 degrees. Maximum temperatures are forecast to exceed 35 degrees Celsius across several major river basins, reaching up to 38 degrees Celsius in parts of Andalusia and Extremadura. AEMET spokesperson Rubén del Campo described the incoming conditions during his Monday briefing.

This week astronomical autumn begins, specifically on the 23rd at 2:25 official peninsular time, but the weather will be full summer.

Regional temperature surges across the peninsula

Interior and western river valleys face the highest maximums during the week. In Andalusia, Seville and Cordoba are forecast to reach 38 degrees Celsius, while Jaen and Granada will also experience sustained high temperatures. The heat is not limited to the southern interior; maximums of 35 degrees Celsius are forecast for Zaragoza, Badajoz, and Ourense, while the Tagus, Guadiana, and Guadalquivir valleys are expected to surpass 36 degrees Celsius. On Sunday, 20 September, Pontevedra recorded a national high of 36.9 degrees Celsius, which was 13 degrees Celsius above its average monthly maximum. Highs between 32 and 34 degrees Celsius are projected for the northern plateau, central Spain, and northeastern regions, while southern areas of Gran Canaria and Fuerteventura are expected to reach between 34 and 36 degrees Celsius.

Atmospheric and marine drivers of the late heat

Meteorologists attribute the prolonged heat to persistent high-pressure systems, clear skies that maximize solar radiation, and warm air masses originating in North Africa. In addition, elevated sea surface temperatures contribute to humidity and warm nighttime conditions along coastal regions. On 12 September, the average Mediterranean sea surface temperature stood at 27.2 degrees Celsius, representing a thermal anomaly of 1.5 to 3.5 degrees Celsius along Spanish shores. Nighttime minimums will also remain elevated in southern coastal and interior provinces, with Seville, Cadiz, Malaga, Jaen, and Almeria experiencing tropical nights. Aside from isolated drizzle and strong easterly winds in the Strait of Gibraltar and Melilla, stable dry conditions will prevail across the mainland through at least Friday, 25 September.

Astronomical transition and seasonal timeline

According to the National Astronomical Observatory, which operates under the National Geographic Institute, the astronomical equinox takes place on Wednesday, 23 September. Different official sources cite the exact peninsular start time at either 02:05 or 02:25. The equinox marks the orbital moment when the Sun crosses the celestial equator southward, making day and night approximately equal in length. Autumn 2026 will last 89 days and 21 hours before concluding on 21 December with the winter solstice. As the season begins, daylight decreases by nearly three minutes each day in mainland Spain, with the sun rising more than one minute later and setting more than one minute earlier each morning and evening. The official shift to winter time will occur on Sunday, 25 October, when clocks move back one hour.