Sonora divides into distinct climate zones: the desert interior is brutally hot from May to September (regularly above 45°C in Hermosillo), while the mountains in the east are cooler year-round and can see snow in winter. The coast is the most reliable in terms of weather — warm from October to May and extremely hot in summer.
October to April is the best time for the coast and desert interior. The weather is warm to hot but manageable, the wildlife is active, and whale watching is possible from January to March along the Sea of Cortez.
November to March is ideal for visiting Álamos and the Sierra Madre foothills, when the heat has broken and the mountains are green from the summer rains.
July and August bring the monsoon to the eastern mountains and foothills — dramatic storms, green landscapes, and waterfalls, but roads can become impassable. The coast at this time is genuinely too hot for most visitors.