This is Waters of March (Aguas de Marco) by Antonio Carlos Jobim sung by the great Elis Regina, who died much too young. Her daughter is the Brazilian singer Maria Rita.
I posted this version, even though it's a little choppy, as it has literal English subtitles. Jobim wrote English lyrics, but these are his original in Portuguese. They're so specific and beautiful. The English lyrics are great, of course, but these are evocative of the end of Summer in Brazil, and much more specific. I think they're much more beautiful. A perfect marriage of word, song, and performer. No wonder some say it's the most beloved Brazilian song of all time.