Tucson baked through an almost endlessly hot October, with hot days averaging more than eight degrees above normal and capping a five-month run of record-breaking or record-tying heat.
October 2024 was not only this cityβs hottest October on record, it also blasted Tucson with the most extreme heat compared to normal of any of the past five months.
Crystal Vaughn, left, takes a drink of water as she and Henry Peralta find a shady spot at Catalina Park, on North Fourth Avenue just south of East Speedway, on one of Tucsonβs hot October days.
High temperatures for October averaged 94.7 degrees, compared to a normal average high for the month of 86.3 degrees. The average daily temperature for October was 78.6 degrees, exactly 6 degrees above normal.
That follows the hottest September on record and a record-tying heat for the summer months of June through August. In addition, the Tucson areaβs monsoon season from June 15 through Sept. 30 was the third-hottest monsoon season on record.
The National Weather Service has kept records of Tucson temperatures and precipitation since 1895.
To cite an extreme example of Octoberβs heat, its average high temperature of 94.7 degrees was only .4 degree lower than the normal average high temperature for September here. Normally, the average October high temperature runs nearly 9 degrees cooler than the average September high temperature.
Overall, October heat was βbonkersβ in Tucson, observed Michael Crimmins, a professor and extension specialist in the University of Arizonaβs Department of Environmental Science.
The extreme weatherβs immediate cause was a high-pressure system β also known as a heat dome β that broke only in Octoberβs last three days. But the blistering month was also a sign that society has not gotten a handle on human-caused climate change, said Crimmins. He does applied research, working with land managers, on both short- and medium-term weather patterns and longer-term climate behavior.
βIt raises the floor. The temperature trend goes up over the whole planet,β Crimmins said of global warming triggered by greenhouse gas emissions. βSo when you do get these heat waves, theyβre starting from a higher spot.β
If the same high pressure-dominated weather pattern had hit Tucson maybe 25-30 years ago, when normal temperatures were cooler than they are today, βit would have definitely been warm. It would have stood out. (But) there would have been a couple of degrees shaved off,β Crimmins said.
In all, October had 17 record-breaking days of high temperatures, as early as Oct. 1 and as late as Oct. 27. Record-breaking heat enveloped Tucson every day but one from Sept. 25 through Oct. 13. The temperature reached or exceeded 100 degrees daily from Sept. 24 through Oct. 13.
βSometimes you have a ridge of high pressure that just wants to park there and is resistant to moving,β said Chris Rasmussen, a National Weather Service meteorologist in Tucson. βThat ridge was so anomalously strong and it just wouldnβt budge. No matter what happened to it, it just wouldnβt budge.β
Average October temperatures also broke records in Phoenix, Flagstaff and Yuma, National Weather Service officials said. Phoenixβs average high temperature for the month of 97.9 degrees was even more extreme than Tucsonβs β at more than 9 degrees above normal.
Flagstaffβs October high temperatures also soared well above average. But at 70.9 degrees, more than seven degrees above normal for the month, they would still feel brisk compared to those of Southern and Central Arizona for the month.
Over the summer and early fall, βthere was an unusual weather pattern we saw across the entire Pacific Ocean,β Crimmins said. βDuring the summer monsoon, weβre under a ridge of high pressure. But if the high pressure ridge is far enough north, it can allow moisture under the ridge to move into the Southwest.
βWe didnβt have a great monsoon. That ridge position wasnβt in a great spot most of the summer. It basically moved around, and sagged south and didnβt give us deep moisture for very long,β Crimmins said. βIt parked overhead. We had a high pressure dome. The moisture got pushed back to the south into Mexico.β
In the end, the entire summer monsoon season was only the 61st wettest on record, when it had been the 13th wettest monsoon period on record from June 15 through Aug. 8.
Looking ahead, the Weather Service forecasts equal chances of above-normal, normal or below-normal temperatures for November. Thatβs a far more moderate monthly forecast than Tucson has seen for some time. Starting at the end of May, every monthly forecast until now βstronglyβ favored a round of above-normal temperatures.
