In the American Midwest: a brief period in September after the first cool, windy days hint of autumn, when the wind calms and a heavy, hazy heat grips the land one last time before fall begins in earnest.

Similiar to, but usually occuring much earlier than an Indian Summer. To see it from a different angle, the "death throes" are the true tail-end of summer, and actually it is the cool, windy day(s) preceding it that are the exceptional weather phenomenon.

Compare with Kiss of February