DANGER ZONE
As temperatures rise, so do safety concerns
Phoenix hasn’t experienced the attentiongetting high temperatures that have approached all-time records this summer, but the city has suffered sustained periods of dangerous heat.
While the highest temperature recorded in 2019 — 115 degrees on July 16 and Aug. 5 — is seven degrees below the all-time record high of 122 on June 26, 1990, the National Weather Service in Phoenix has issued six excessive heat warnings this spring and summer. That compares to seven at this point in 2018 (eight total that year) and only four in 2017 despite the city seeing a high of 119 in June and 118 in July of that year.
Paul Iñiguez, science and operations officer with the Weather Service’s Phoenix office, said Phoenixarea residents need to pay attention to what’s going on this summer.
“It’s hot, even by our standards,” Iñiguez said. “It doesn’t have to be 120 (degrees) for people to have problems.”
According to the Maricopa County Department of Public Health, there have been 25 heat-caused or heat-related deaths in the county since April 28 (the start of the enhanced surveillance period) with 119 cases still under investigation as of Aug. 14.
Thermometers at the official reporting station at Sky Harbor Airport have recorded only three high-temperature records in 2019, compared to six by this point in 2018 and five in 2017.
That could change this week, however, as the forecast highs of 112 degrees on Aug. 20 and 114 degrees on Aug. 21 would set records for those dates if reached.
This year Phoenix has broken or tied record highs on June 12 (112 degrees), Aug. 3 (114) and Aug. 5 (115).
Again, it doesn’t take eye-popping temperatures to cause problems.
The average high temperature for the month through Aug. 18 is 108.3 degrees. That’s 3.7 degrees above normal. The average overnight low temperature for August 2019 is 85.9 degrees (normal is 83.2).
That makes the average temperature for the month (taking the average high and low and dividing by two) 97.1 degrees, which is 3.2 degrees above normal.
The year started off cooler than normal and year-to-date temperatures in all three categories are still slightly below average (all within one degree) as of Aug. 18. However, the recent heatwaves have been closing that gap and temperatures will likely be above normal by the end of summer.
The average temperature of 97.1 degrees for the period between July 15 and August 15 is the hottest on record for that period, Iñiguez said.
The cause of the high heat also explains, in large part, the lack of rainfall in the area this summer. The area of high pressure necessary to bring moisture from the south and fuel monsoon storms has been in the wrong position for most of the season.
Instead of being off to the northeast of the state which would result in moist southerly winds, it has spent a lot of time directly over Arizona, or in a position where clockwise airflow around the high has not been conducive to the development of clouds or storms.
Phoenix has seen only .27 of an inch of rain since the start of the monsoon season on June 15. That’s more than an inch below normal as of Aug. 19.
According to the National Oceanic and Atmospheric Administration, areas of high-pressure act as a kind of cap on the atmosphere, which inhibits air from rising and forming clouds. It also blocks storm systems from moving into the area. As a result, the sun has more time to heat the ground. With less of that energy used to evaporate moisture, temperatures can climb.
University of Arizona climate scientist Mike Crimmins said there have been a variety of factors keeping the high pressure out of the position needed for summer rains. The lack of rain has contributed to the extended periods of heat.
“The moisture is typically how we can temper some of these hot spells in the middle of the summertime,” Crimmins said. “It’s just getting some (rain) and cooling of the lower levels of the atmosphere and (having) clouds. If you take those off the table and put the high-pressure overhead in August, we’re going to bake.”
While the current National Weather Service forecast still isn’t calling for rain, there is some relief from extreme temperatures expected.
Highs are expected to fall back below 110 degrees by Friday, Aug. 23 and return closer to normal (104 degrees) by the weekend.
Though we can still get extreme temperatures in August (the record high for the month is 117 degrees on Aug. 14, 2015 and Aug. 26, 2011), the weather should get more comfortable as fall approaches.
There is even a possibility that we could still get some rain from the remnants of a late-season tropical storm or hurricane activity in the eastern Pacific Ocean making its way into the area.