In article ,
Steve Jones writes:
I don't understand all this talk of an Indian summer for September. It
is still summer! At least till the autumnal equinox anyway.

What gives?

I don't think that this question is included in the newsgroup FAQ, but
the number of times it comes up perhaps it should be. As far as
meteorologists and climatologists are concerned, summer comprises the
months of June, July and August. Not only is it more convenient to have
seasons comprising complete months, but also the weather in June is
typically more summer-like than spring-like while in September it tends
to be more autumnal than summery.
--
John Hall "[It was] so steep that at intervals the street broke into steps,
like a person breaking into giggles or hiccups, and then resumed
its sober climb, until it had another fit of steps."
Ursula K Le Guin "The Beginning Place"