The best months to go to Andalusia are October and November, and April and May.
Andalusia is blisteringly hot in the summer. If summer is your only chance to come, plan time in the Sierra de Aracena in Huelva, the Pedroches of northern Córdoba province, Granada's Sierra Nevada and Alpujarra highlands, or the Sierra de Cazorla in Jaén. Autumn catches the cities going about their business, the temperatures are moderate, and you will rarely see a line form. The months between December and April tend to be cool, uncrowded, and quiet. But come spring, it's fiesta time, with Seville's Semana Santa (Holy Week) the most moving and multitudinous. April showcases whitewashed Andalusia at its floral best, every patio and facade covered with everything from bougainvillea to honeysuckle.