If you want to circle a day on your calendar when things will start to cool off, your best bet is Oct. 5. According to the National Weather Service, that’s the average point each year over the past three decades when Phoenix experienced its last 100-degree day.
This year, “those highs might be hovering around 100 no later than the beginning of October," NWS Phoenix lead meteorologist Alex Young said.
Last year, the city’s last 100-degree day was Oct. 21. However, in 2022, it was significantly earlier, on Sept. 29.
The latest that Phoenix had its last 100-degree day in the past 20 years was in 2016. That year, residents had to wait until the end of Oct. 27 for the triple-digit days of summer to finally end. The earliest Phoenix has welcomed its last 100-degree day is Sept. 19, which was the case in 2019, 2017 and 1998.
The last 100-degree day in Phoenix over the past 30 years, according to National Weather Service data.
Morgan Fischer
Don’t count on such an early arrival of fall in the future. Summer in Phoenix is expected to last longer than in years past. According to NWS’s Climate Prediction Center, temperatures from September through November are expected to be “above normal,” Young said.
Phoenix has weathered 53 days this year with temperatures higher than 110 degrees, which is only two days shy of the record set in 2023. That record might fall soon — Phoenix already has endured more days above 110 this year than it had by this point one year ago.
As of Aug. 27, the city also has fittingly had 100 days of temperatures 100 degrees or hotter. Over the past 30 years, Phoenix has had an average of 111 triple-digit degree days per year.
While the city will continue to “see high temperatures through at least the middle of September,” Young said, the end of 100-plus-degree days is nearing. The NWS predicts Phoenix will top out at only 100 degrees on Sept. 17, the first time since May 26 the Valley won’t have hit 101.
