Another record-hot month socked Tucson
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 city's hottest October on record, it also blasted Tucson with the most extreme heat compared to normal of any of the past five months.
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 area's 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 October's 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 "bonkers" in Tucson, observed Michael Crimmins, a professor and extension specialist in the University of Arizona's Department of Environmental Science.
The extreme weather's immediate cause was a high-pressure system — also known as a heat dome — that broke only in October's 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.
"It raises the floor. The temperature trend goes up over the whole planet," Crimmins said of global warming triggered by greenhouse gas emissions. "So when you do get these heat waves, they're starting from a higher spot."
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, "it would have definitely been warm. It would have stood out. (But) there would have been a couple of degrees shaved off," 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.
"Sometimes you have a ridge of high pressure that just wants to park there and is resistant to moving," said Chris Rasmussen, a National Weather Service meteorologist in Tucson. "That ridge was so anomalously strong and it just wouldn't budge. No matter what happened to it, it just wouldn't budge."
Average October temperatures also broke records in Phoenix, Flagstaff and Yuma, National Weather Service officials said. Phoenix's average high temperature for the month of 97.9 degrees was even more extreme than Tucson's — at more than 9 degrees above normal.
Flagstaff's 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, "there was an unusual weather pattern we saw across the entire Pacific Ocean," Crimmins said. "During the summer monsoon, we're 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.
"We didn't have a great monsoon. That ridge position wasn't in a great spot most of the summer. It basically moved around, and sagged south and didn't give us deep moisture for very long," Crimmins said. "It parked overhead. We had a high pressure dome. The moisture got pushed back to the south into Mexico."
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. That's a far more moderate monthly forecast than Tucson has seen for some time. Starting at the end of May, every monthly forecast until now "strongly" favored a round of above-normal temperatures.
Contact Tony Davis at 520-349-0350 or . Follow Davis on .
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