Santa Cruz is tropical: hot and humid most of the year, with two clear seasons.
April to October is the dry season and the best time to visit. Days are warm rather than scorching, nights are pleasant, and the surrounding parks and Mission routes are accessible. Occasional cold fronts called surazos sweep up from Argentina in June and July, dropping temperatures sharply for a few days.
November to March is the rainy season. Heat and humidity build to oppressive levels, afternoon downpours are routine, and the dirt roads into Amboró and the Pantanal become difficult or impassable. The city itself remains green and functional, but excursions are riskier.
If you can choose, aim for May, June, August, or September — dry, warm, and uncrowded.