December - the beginning of summer in Rio de Janeiro. During the summer months (December - March) it becomes hotter and slightly higher humidity. December and January are the hottest months of the year in Rio de Janeiro, during the day the air temperature rises to +40 ° C. But the humidity is not very high.

In December (and in general in summer) slightly more rain falls, showers are possible, more often than in winter, drizzles warm rain.