In September, the Algarve region and the Alentejo interior are consistently the hottest parts of Portugal. While the peak summer heat of August begins to subside, the southern coast maintains a very warm Mediterranean climate with average daytime highs ranging from 26°C to 30°C (79°F to 86°F). However, for absolute peak heat, the city of Évora and the surrounding Alentejo plains often see higher temperatures than the coast, sometimes reaching 32°C (90°F), because they lack the cooling influence of the Atlantic breezes. The seawater in the Algarve is also at its warmest in September, having been heated throughout the summer, making it the premier destination for sun-seekers. In contrast, northern cities like Porto and the Douro Valley begin to see more frequent breezes and slightly cooler evenings. September is widely considered the "sweet spot" for Portuguese travel, as you can still enjoy the scorching southern sun without the oppressive humidity or the massive "high season" crowds that dominate July and August, while the central regions remain perfectly "summer-like" throughout the month.