Hermosillo is brutally hot in summer. July and August regularly see temperatures above 45°C (113°F) — the city holds the Mexican record for highest recorded temperature. You can still visit, but you will be spending much of your time inside air-conditioned spaces. April, May, and October are the most comfortable months; winters are mild and pleasant.
The rainy season runs from late June through September, with brief but heavy afternoon thunderstorms that provide temporary relief from the heat. The festival of San Francisco de Asís in early October brings celebrations to the city; the Day of the Dead at the end of October is observed with elaborately decorated altars in the market and public spaces.