Winter—June through September—is high season in the Pantanal. Temperatures are at their coolest, with averages in the low 80s, occasional peaks in the high 90s, and troughs in the low 50s during cold fronts. It’s also when water levels are at their lowest and wildlife is easiest to see—usually concentrated along the remaining rivers and lakes, which have a high concentration of fish. Look out for caiman, herons, kingfishers, and other water birds. Anacondas can sometimes be seen crossing dirt roads in search of water. August and September are the best months to see jaguar, again near water, either at the far south of Transpantaneira road in Mato Grosso or along the Rio Vermelho River in Mato Grosso do Sul.
Temperatures and humidity rise in October and November. Visits are still possible, but there are frequent thunderstorms and animals begin to disperse. By December, the rains are fully underway, and many of the ranch-house lodges close up for low season. Sometime before Christmas, rivers in the north burst their banks and the flatland savannas of the northern Pantanal get completely submerged. The floods spread into the southern Pantanal a month or so later, when the few lodges that remain open offer tours only by boat, and animals and cattle crowd together on forested islands. The Pantanal is astonishingly beautiful at this time, but 100-plus-degree temperatures, 80 percent humidity, and clouds of mosquitoes make it uncomfortable.