Japan had its second-hottest September since records began with some regions the warmest yet, the weather agency said, in a year likely to become the warmest in human history.

The month kicked off with triple-digit temperatures in many parts of the state, with millions of Californians under heat advisories through at least Thursday.

Phoenix is in the throes of an unprecedented heat wave expected to last at least until the end of the week. Reality check: Our summers have always been hot, but recently they've been feeling longer, too.