What do they call that, Indian Summer?

The sun stays summer hot even though autumn mornings have started.
It seems the season, from its heated theme, refuses to be parted.
One half the day will verify the time of year has changed,
and the last, sent sun coursing orange through fresh brushed breathy air,
will remain stiflingly familiar. For the next several years,
the seasons are not foretold by calendars.