Phoenix wrapped up its annual six-month warm season this week after the Southwest broiled through an unprecedented autumn heat wave.

Axios Visuals After having its hottest summer on record, Phoenix saw an unprecedented and sustained heat wave during parts of September through mid-October. Why it matters: The latest stretch prolonged heat-related health threats and pointed to the growing challenge of how to be resilient in the face of scorching temperatures.

A record breaking heat wave in the West could begin to subside this week, with high temperatures in Phoenix projected to drop to below 100 degrees for the first time since May, ending a record stretch of brutal heat.

Previous record highs in the city of Napa, as well in the city of Santa Rosa — both made in 1980 — were either tied or broken last week, officials said, while a third local record, set in 1930, may have been broken on Sunday.

Arizona, Nevada and New Mexico have had unseasonably warm fall temperatures 10 to 20 degrees above average. The heat in Phoenix has been particularly extreme.